API Reference
Preliminaries
All declarations are in :file:`jansson.h`, so it’s enough to
in each source file.
All constants are prefixed with JSON_ (except for those describing
the library version, prefixed with JANSSON_). Other identifiers
are prefixed with json_. Type names are suffixed with _t and
typedef‘d so that the struct keyword need not be used.
Library Version
The Jansson version is of the form A.B.C, where A is the major
version, B is the minor version and C is the micro version. If the
micro version is zero, it’s omitted from the version string, i.e. the
version string is just A.B.
When a new release only fixes bugs and doesn’t add new features or
functionality, the micro version is incremented. When new features are
added in a backwards compatible way, the minor version is incremented
and the micro version is set to zero. When there are backwards
incompatible changes, the major version is incremented and others are
set to zero.
The following preprocessor constants specify the current version of
the library:
JANSSON_MAJOR_VERSION,JANSSON_MINOR_VERSION,JANSSON_MICRO_VERSION- Integers specifying the major, minor and micro versions,
respectively. JANSSON_VERSION- A string representation of the current version, e.g.
"1.2.1"or
"1.3". JANSSON_VERSION_HEX-
A 3-byte hexadecimal representation of the version, e.g.
0x010201for version 1.2.1 and0x010300for version 1.3.
This is useful in numeric comparisons, e.g.:#if JANSSON_VERSION_HEX >= 0x010300 /* Code specific to version 1.3 and above */ #endif
Additionally, there are functions to determine the version of Jansson at
runtime:
.. function:: const char *jansson_version_str() Return the version of the Jansson library, in the same format as the ``JANSSON_VERSION`` preprocessor constant. .. versionadded:: 2.13
.. function:: int jansson_version_cmp(int major, int minor, int micro) Returns an integer less than, equal to, or greater than zero if the runtime version of Jansson is found, respectively, to be less than, to match, or be greater than the provided *major*, *minor*, and *micro*. .. versionadded:: 2.13
JANSSON_THREAD_SAFE_REFCOUNT- If this value is defined all read-only operations and reference counting in
Jansson are thread safe. This value is not defined for versions older than
2.11or when the compiler does not provide built-in atomic functions.
Value Representation
The JSON specification (RFC 4627) defines the following data types:
object, array, string, number, boolean, and null. JSON
types are used dynamically; arrays and objects can hold any other data
type, including themselves. For this reason, Jansson’s type system is
also dynamic in nature. There’s one C type to represent all JSON
values, and this structure knows the type of the JSON value it holds.
.. type:: json_t This data structure is used throughout the library to represent all JSON values. It always contains the type of the JSON value it holds and the value's reference count. The rest depends on the type of the value.
Objects of :type:`json_t` are always used through a pointer. There
are APIs for querying the type, manipulating the reference count, and
for constructing and manipulating values of different types.
Unless noted otherwise, all API functions return an error value if an
error occurs. Depending on the function’s signature, the error value
is either NULL or -1. Invalid arguments or invalid input are
apparent sources for errors. Memory allocation and I/O operations may
also cause errors.
Type
.. c:enum:: json_type The type of a JSON value. The following members are defined: +--------------------+ | ``JSON_OBJECT`` | +--------------------+ | ``JSON_ARRAY`` | +--------------------+ | ``JSON_STRING`` | +--------------------+ | ``JSON_INTEGER`` | +--------------------+ | ``JSON_REAL`` | +--------------------+ | ``JSON_TRUE`` | +--------------------+ | ``JSON_FALSE`` | +--------------------+ | ``JSON_NULL`` | +--------------------+ These correspond to JSON object, array, string, number, boolean and null. A number is represented by either a value of the type ``JSON_INTEGER`` or of the type ``JSON_REAL``. A true boolean value is represented by a value of the type ``JSON_TRUE`` and false by a value of the type ``JSON_FALSE``.
.. function:: int json_typeof(const json_t *json) Return the type of the JSON value (a :type:`json_type` cast to ``int``). *json* MUST NOT be *NULL*. This function is actually implemented as a macro for speed.
.. function:: int json_is_object(const json_t *json) int json_is_array(const json_t *json) int json_is_string(const json_t *json) int json_is_integer(const json_t *json) int json_is_real(const json_t *json) int json_is_true(const json_t *json) int json_is_false(const json_t *json) int json_is_null(const json_t *json) These functions (actually macros) return true (non-zero) for values of the given type, and false (zero) for values of other types and for *NULL*.
.. function:: int json_is_number(const json_t *json) Returns true for values of types ``JSON_INTEGER`` and ``JSON_REAL``, and false for other types and for *NULL*.
.. function:: int json_is_boolean(const json_t *json) Returns true for types ``JSON_TRUE`` and ``JSON_FALSE``, and false for values of other types and for *NULL*.
.. function:: int json_boolean_value(const json_t *json) Alias of :func:`json_is_true()`, i.e. returns 1 for ``JSON_TRUE`` and 0 otherwise. .. versionadded:: 2.7
Reference Count
The reference count is used to track whether a value is still in use
or not. When a value is created, it’s reference count is set to 1. If
a reference to a value is kept (e.g. a value is stored somewhere for
later use), its reference count is incremented, and when the value is
no longer needed, the reference count is decremented. When the
reference count drops to zero, there are no references left, and the
value can be destroyed.
.. function:: json_t *json_incref(json_t *json) Increment the reference count of *json* if it's not *NULL*. Returns *json*.
.. function:: void json_decref(json_t *json) Decrement the reference count of *json*. As soon as a call to :func:`json_decref()` drops the reference count to zero, the value is destroyed and it can no longer be used.
Functions creating new JSON values set the reference count to 1. These
functions are said to return a new reference. Other functions
returning (existing) JSON values do not normally increase the
reference count. These functions are said to return a borrowed
reference. So, if the user will hold a reference to a value returned
as a borrowed reference, he must call :func:`json_incref`. As soon as
the value is no longer needed, :func:`json_decref` should be called
to release the reference.
Normally, all functions accepting a JSON value as an argument will
manage the reference, i.e. increase and decrease the reference count
as needed. However, some functions steal the reference, i.e. they
have the same result as if the user called :func:`json_decref()` on
the argument right after calling the function. These functions are
suffixed with _new or have _new_ somewhere in their name.
For example, the following code creates a new JSON array and appends
an integer to it:
json_t *array, *integer; array = json_array(); integer = json_integer(42); json_array_append(array, integer); json_decref(integer);
Note how the caller has to release the reference to the integer value
by calling :func:`json_decref()`. By using a reference stealing
function :func:`json_array_append_new()` instead of
:func:`json_array_append()`, the code becomes much simpler:
json_t *array = json_array(); json_array_append_new(array, json_integer(42));
In this case, the user doesn’t have to explicitly release the
reference to the integer value, as :func:`json_array_append_new()`
steals the reference when appending the value to the array.
In the following sections it is clearly documented whether a function
will return a new or borrowed reference or steal a reference to its
argument.
Circular References
A circular reference is created when an object or an array is,
directly or indirectly, inserted inside itself. The direct case is
simple:
json_t *obj = json_object(); json_object_set(obj, "foo", obj);
Jansson will refuse to do this, and :func:`json_object_set()` (and
all the other such functions for objects and arrays) will return with
an error status. The indirect case is the dangerous one:
json_t *arr1 = json_array(), *arr2 = json_array(); json_array_append(arr1, arr2); json_array_append(arr2, arr1);
In this example, the array arr2 is contained in the array
arr1, and vice versa. Jansson cannot check for this kind of
indirect circular references without a performance hit, so it’s up to
the user to avoid them.
If a circular reference is created, the memory consumed by the values
cannot be freed by :func:`json_decref()`. The reference counts never
drops to zero because the values are keeping the references to each
other. Moreover, trying to encode the values with any of the encoding
functions will fail. The encoder detects circular references and
returns an error status.
Scope Dereferencing
It is possible to use the json_auto_t type to automatically
dereference a value at the end of a scope. For example:
void function(void) { json_auto_t *value = NULL; value = json_string("foo"); /* json_decref(value) is automatically called. */ }
This feature is only available on GCC and Clang. So if your project
has a portability requirement for other compilers, you should avoid
this feature.
Additionally, as always, care should be taken when passing values to
functions that steal references.
True, False and Null
These three values are implemented as singletons, so the returned
pointers won’t change between invocations of these functions.
.. function:: json_t *json_true(void) .. refcounting:: new Returns the JSON true value.
.. function:: json_t *json_false(void) .. refcounting:: new Returns the JSON false value.
.. function:: json_t *json_boolean(val) .. refcounting:: new Returns JSON false if ``val`` is zero, and JSON true otherwise. This is a macro, and equivalent to ``val ? json_true() : json_false()``. .. versionadded:: 2.4
.. function:: json_t *json_null(void) .. refcounting:: new Returns the JSON null value.
String
Jansson uses UTF-8 as the character encoding. All JSON strings must be
valid UTF-8 (or ASCII, as it’s a subset of UTF-8). All Unicode
codepoints U+0000 through U+10FFFF are allowed, but you must use
length-aware functions if you wish to embed null bytes in strings.
.. function:: json_t *json_string(const char *value) .. refcounting:: new Returns a new JSON string, or *NULL* on error. *value* must be a valid null terminated UTF-8 encoded Unicode string.
.. function:: json_t *json_stringn(const char *value, size_t len) .. refcounting:: new Like :func:`json_string`, but with explicit length, so *value* may contain null characters or not be null terminated. .. versionadded:: 2.7
.. function:: json_t *json_string_nocheck(const char *value) .. refcounting:: new Like :func:`json_string`, but doesn't check that *value* is valid UTF-8. Use this function only if you are certain that this really is the case (e.g. you have already checked it by other means).
.. function:: json_t *json_stringn_nocheck(const char *value, size_t len) .. refcounting:: new Like :func:`json_string_nocheck`, but with explicit length, so *value* may contain null characters or not be null terminated. .. versionadded:: 2.7
.. function:: const char *json_string_value(const json_t *string) Returns the associated value of *string* as a null terminated UTF-8 encoded string, or *NULL* if *string* is not a JSON string. The returned value is read-only and must not be modified or freed by the user. It is valid as long as *string* exists, i.e. as long as its reference count has not dropped to zero.
.. function:: size_t json_string_length(const json_t *string) Returns the length of *string* in its UTF-8 presentation, or zero if *string* is not a JSON string. .. versionadded:: 2.7
.. function:: int json_string_set(json_t *string, const char *value) Sets the associated value of *string* to *value*. *value* must be a valid UTF-8 encoded Unicode string. Returns 0 on success and -1 on error.
.. function:: int json_string_setn(json_t *string, const char *value, size_t len) Like :func:`json_string_set`, but with explicit length, so *value* may contain null characters or not be null terminated. .. versionadded:: 2.7
.. function:: int json_string_set_nocheck(json_t *string, const char *value) Like :func:`json_string_set`, but doesn't check that *value* is valid UTF-8. Use this function only if you are certain that this really is the case (e.g. you have already checked it by other means).
.. function:: int json_string_setn_nocheck(json_t *string, const char *value, size_t len) Like :func:`json_string_set_nocheck`, but with explicit length, so *value* may contain null characters or not be null terminated. .. versionadded:: 2.7
.. function:: json_t *json_sprintf(const char *format, ...) json_t *json_vsprintf(const char *format, va_list ap) .. refcounting:: new Construct a JSON string from a format string and varargs, just like :func:`printf()`. .. versionadded:: 2.11
Number
The JSON specification only contains one numeric type, «number». The C
programming language has distinct types for integer and floating-point
numbers, so for practical reasons Jansson also has distinct types for
the two. They are called «integer» and «real», respectively. For more
information, see :ref:`rfc-conformance`.
.. type:: json_int_t This is the C type that is used to store JSON integer values. It represents the widest integer type available on your system. In practice it's just a typedef of ``long long`` if your compiler supports it, otherwise ``long``. Usually, you can safely use plain ``int`` in place of ``json_int_t``, and the implicit C integer conversion handles the rest. Only when you know that you need the full 64-bit range, you should use ``json_int_t`` explicitly.
JSON_INTEGER_IS_LONG_LONG-
This is a preprocessor variable that holds the value 1 if
:type:`json_int_t` islong long, and 0 if it’slong. It
can be used as follows:#if JSON_INTEGER_IS_LONG_LONG /* Code specific for long long */ #else /* Code specific for long */ #endif
JSON_INTEGER_FORMAT-
This is a macro that expands to a :func:`printf()` conversion
specifier that corresponds to :type:`json_int_t`, without the
leading%sign, i.e. either"lld"or"ld". This macro
is required because the actual type of :type:`json_int_t` can be
eitherlongorlong long, and :func:`printf()` requires
different length modifiers for the two.Example:
json_int_t x = 123123123; printf("x is %" JSON_INTEGER_FORMAT "n", x);
.. function:: json_t *json_integer(json_int_t value) .. refcounting:: new Returns a new JSON integer, or *NULL* on error.
.. function:: json_int_t json_integer_value(const json_t *integer) Returns the associated value of *integer*, or 0 if *json* is not a JSON integer.
.. function:: int json_integer_set(const json_t *integer, json_int_t value) Sets the associated value of *integer* to *value*. Returns 0 on success and -1 if *integer* is not a JSON integer.
.. function:: json_t *json_real(double value) .. refcounting:: new Returns a new JSON real, or *NULL* on error.
.. function:: double json_real_value(const json_t *real) Returns the associated value of *real*, or 0.0 if *real* is not a JSON real.
.. function:: int json_real_set(const json_t *real, double value) Sets the associated value of *real* to *value*. Returns 0 on success and -1 if *real* is not a JSON real.
.. function:: double json_number_value(const json_t *json) Returns the associated value of the JSON integer or JSON real *json*, cast to double regardless of the actual type. If *json* is neither JSON real nor JSON integer, 0.0 is returned.
Array
A JSON array is an ordered collection of other JSON values.
.. function:: json_t *json_array(void) .. refcounting:: new Returns a new JSON array, or *NULL* on error. Initially, the array is empty.
.. function:: size_t json_array_size(const json_t *array) Returns the number of elements in *array*, or 0 if *array* is NULL or not a JSON array.
.. function:: json_t *json_array_get(const json_t *array, size_t index) .. refcounting:: borrow Returns the element in *array* at position *index*. The valid range for *index* is from 0 to the return value of :func:`json_array_size()` minus 1. If *array* is not a JSON array, if *array* is *NULL*, or if *index* is out of range, *NULL* is returned.
.. function:: int json_array_set(json_t *array, size_t index, json_t *value) Replaces the element in *array* at position *index* with *value*. The valid range for *index* is from 0 to the return value of :func:`json_array_size()` minus 1. Returns 0 on success and -1 on error.
.. function:: int json_array_set_new(json_t *array, size_t index, json_t *value) Like :func:`json_array_set()` but steals the reference to *value*. This is useful when *value* is newly created and not used after the call.
.. function:: int json_array_append(json_t *array, json_t *value) Appends *value* to the end of *array*, growing the size of *array* by 1. Returns 0 on success and -1 on error.
.. function:: int json_array_append_new(json_t *array, json_t *value) Like :func:`json_array_append()` but steals the reference to *value*. This is useful when *value* is newly created and not used after the call.
.. function:: int json_array_insert(json_t *array, size_t index, json_t *value) Inserts *value* to *array* at position *index*, shifting the elements at *index* and after it one position towards the end of the array. Returns 0 on success and -1 on error.
.. function:: int json_array_insert_new(json_t *array, size_t index, json_t *value) Like :func:`json_array_insert()` but steals the reference to *value*. This is useful when *value* is newly created and not used after the call.
.. function:: int json_array_remove(json_t *array, size_t index) Removes the element in *array* at position *index*, shifting the elements after *index* one position towards the start of the array. Returns 0 on success and -1 on error. The reference count of the removed value is decremented.
.. function:: int json_array_clear(json_t *array) Removes all elements from *array*. Returns 0 on success and -1 on error. The reference count of all removed values are decremented.
.. function:: int json_array_extend(json_t *array, json_t *other_array) Appends all elements in *other_array* to the end of *array*. Returns 0 on success and -1 on error.
.. function:: void json_array_foreach(array, index, value) Iterate over every element of ``array``, running the block of code that follows each time with the proper values set to variables ``index`` and ``value``, of types :type:`size_t` and :type:`json_t` pointer respectively. Example:: /* array is a JSON array */ size_t index; json_t *value; json_array_foreach(array, index, value) { /* block of code that uses index and value */ } The items are returned in increasing index order. This macro expands to an ordinary ``for`` statement upon preprocessing, so its performance is equivalent to that of hand-written code using the array access functions. The main advantage of this macro is that it abstracts away the complexity, and makes for more concise and readable code. .. versionadded:: 2.5
Object
A JSON object is a dictionary of key-value pairs, where the key is a
Unicode string and the value is any JSON value.
Even though null bytes are allowed in string values, they are not
allowed in object keys.
.. function:: json_t *json_object(void) .. refcounting:: new Returns a new JSON object, or *NULL* on error. Initially, the object is empty.
.. function:: size_t json_object_size(const json_t *object) Returns the number of elements in *object*, or 0 if *object* is not a JSON object.
.. function:: json_t *json_object_get(const json_t *object, const char *key) .. refcounting:: borrow Get a value corresponding to *key* from *object*. Returns *NULL* if *key* is not found and on error.
.. function:: json_t *json_object_getn(const json_t *object, const char *key, size_t key_len) .. refcounting:: borrow Like :func:`json_object_get`, but give the fixed-length *key* with length *key_len*. See :ref:`fixed_length_keys` for details. .. versionadded:: 2.14
.. function:: int json_object_set(json_t *object, const char *key, json_t *value) Set the value of *key* to *value* in *object*. *key* must be a valid null terminated UTF-8 encoded Unicode string. If there already is a value for *key*, it is replaced by the new value. Returns 0 on success and -1 on error.
.. function:: int json_object_setn(json_t *object, const char *key, size_t key_len, json_t *value) Like :func:`json_object_set`, but give the fixed-length *key* with length *key_len*. See :ref:`fixed_length_keys` for details. .. versionadded:: 2.14
.. function:: int json_object_set_nocheck(json_t *object, const char *key, json_t *value) Like :func:`json_object_set`, but doesn't check that *key* is valid UTF-8. Use this function only if you are certain that this really is the case (e.g. you have already checked it by other means).
.. function:: int json_object_setn_nocheck(json_t *object, const char *key, size_t key_len, json_t *value) Like :func:`json_object_set_nocheck`, but give the fixed-length *key* with length *key_len*. See :ref:`fixed_length_keys` for details. .. versionadded:: 2.14
.. function:: int json_object_set_new(json_t *object, const char *key, json_t *value) Like :func:`json_object_set()` but steals the reference to *value*. This is useful when *value* is newly created and not used after the call.
.. function:: int json_object_setn_new(json_t *object, const char *key, size_t key_len, json_t *value) Like :func:`json_object_set_new`, but give the fixed-length *key* with length *key_len*. See :ref:`fixed_length_keys` for details. .. versionadded:: 2.14
.. function:: int json_object_set_new_nocheck(json_t *object, const char *key, json_t *value) Like :func:`json_object_set_new`, but doesn't check that *key* is valid UTF-8. Use this function only if you are certain that this really is the case (e.g. you have already checked it by other means).
.. function:: int json_object_setn_new_nocheck(json_t *object, const char *key, size_t key_len, json_t *value) Like :func:`json_object_set_new_nocheck`, but give the fixed-length *key* with length *key_len*. See :ref:`fixed_length_keys` for details. .. versionadded:: 2.14
.. function:: int json_object_del(json_t *object, const char *key) Delete *key* from *object* if it exists. Returns 0 on success, or -1 if *key* was not found. The reference count of the removed value is decremented.
.. function:: int json_object_deln(json_t *object, const char *key, size_t key_len) Like :func:`json_object_del`, but give the fixed-length *key* with length *key_len*. See :ref:`fixed_length_keys` for details. .. versionadded:: 2.14
.. function:: int json_object_clear(json_t *object) Remove all elements from *object*. Returns 0 on success and -1 if *object* is not a JSON object. The reference count of all removed values are decremented.
.. function:: int json_object_update(json_t *object, json_t *other) Update *object* with the key-value pairs from *other*, overwriting existing keys. Returns 0 on success or -1 on error.
.. function:: int json_object_update_existing(json_t *object, json_t *other) Like :func:`json_object_update()`, but only the values of existing keys are updated. No new keys are created. Returns 0 on success or -1 on error. .. versionadded:: 2.3
.. function:: int json_object_update_missing(json_t *object, json_t *other) Like :func:`json_object_update()`, but only new keys are created. The value of any existing key is not changed. Returns 0 on success or -1 on error. .. versionadded:: 2.3
.. function:: int json_object_update_new(json_t *object, json_t *other) Like :func:`json_object_update()`, but steals the reference to *other*. This is useful when *other* is newly created and not used after the call.
.. function:: int json_object_update_existing_new(json_t *object, json_t *other) Like :func:`json_object_update_new()`, but only the values of existing keys are updated. No new keys are created. Returns 0 on success or -1 on error.
.. function:: int json_object_update_missing_new(json_t *object, json_t *other) Like :func:`json_object_update_new()`, but only new keys are created. The value of any existing key is not changed. Returns 0 on success or -1 on error.
.. function:: int json_object_update_recursive(json_t *object, json_t *other) Like :func:`json_object_update()`, but object values in *other* are recursively merged with the corresponding values in *object* if they are also objects, instead of overwriting them. Returns 0 on success or -1 on error.
.. function:: void json_object_foreach(object, key, value) Iterate over every key-value pair of ``object``, running the block of code that follows each time with the proper values set to variables ``key`` and ``value``, of types ``const char *`` and :type:`json_t` pointer respectively. Example:: /* obj is a JSON object */ const char *key; json_t *value; json_object_foreach(obj, key, value) { /* block of code that uses key and value */ } The items are returned in the order they were inserted to the object. **Note:** It's not safe to call ``json_object_del(object, key)`` or ``json_object_deln(object, key, key_len)`` during iteration. If you need to, use :func:`json_object_foreach_safe` instead. This macro expands to an ordinary ``for`` statement upon preprocessing, so its performance is equivalent to that of hand-written iteration code using the object iteration protocol (see below). The main advantage of this macro is that it abstracts away the complexity behind iteration, and makes for more concise and readable code. .. versionadded:: 2.3
.. function:: void json_object_foreach_safe(object, tmp, key, value) Like :func:`json_object_foreach()`, but it's safe to call ``json_object_del(object, key)`` or ``json_object_deln(object, key, key_len)`` during iteration. You need to pass an extra ``void *`` parameter ``tmp`` that is used for temporary storage. .. versionadded:: 2.8
.. function:: void json_object_keylen_foreach(object, key, key_len, value) Like :c:func:`json_object_foreach`, but in *key_len* stored length of the *key*. Example:: /* obj is a JSON object */ const char *key; json_t *value; size_t len; json_object_keylen_foreach(obj, key, len, value) { printf("got key %s with length %zun", key, len); } **Note:** It's not safe to call ``json_object_deln(object, key, key_len)`` during iteration. If you need to, use :func:`json_object_keylen_foreach_safe` instead. .. versionadded:: 2.14
.. function:: void json_object_keylen_foreach_safe(object, tmp, key, key_len, value) Like :func:`json_object_keylen_foreach()`, but it's safe to call ``json_object_deln(object, key, key_len)`` during iteration. You need to pass an extra ``void *`` parameter ``tmp`` that is used for temporary storage. .. versionadded:: 2.14
The following functions can be used to iterate through all key-value
pairs in an object. The items are returned in the order they were
inserted to the object.
.. function:: void *json_object_iter(json_t *object) Returns an opaque iterator which can be used to iterate over all key-value pairs in *object*, or *NULL* if *object* is empty.
.. function:: void *json_object_iter_at(json_t *object, const char *key) Like :func:`json_object_iter()`, but returns an iterator to the key-value pair in *object* whose key is equal to *key*, or NULL if *key* is not found in *object*. Iterating forward to the end of *object* only yields all key-value pairs of the object if *key* happens to be the first key in the underlying hash table.
.. function:: void *json_object_iter_next(json_t *object, void *iter) Returns an iterator pointing to the next key-value pair in *object* after *iter*, or *NULL* if the whole object has been iterated through.
.. function:: const char *json_object_iter_key(void *iter) Extract the associated key from *iter*.
.. function:: size_t json_object_iter_key_len(void *iter) Extract the associated key length from *iter*. .. versionadded:: 2.14
.. function:: json_t *json_object_iter_value(void *iter) .. refcounting:: borrow Extract the associated value from *iter*.
.. function:: int json_object_iter_set(json_t *object, void *iter, json_t *value) Set the value of the key-value pair in *object*, that is pointed to by *iter*, to *value*.
.. function:: int json_object_iter_set_new(json_t *object, void *iter, json_t *value) Like :func:`json_object_iter_set()`, but steals the reference to *value*. This is useful when *value* is newly created and not used after the call.
.. function:: void *json_object_key_to_iter(const char *key) Like :func:`json_object_iter_at()`, but much faster. Only works for values returned by :func:`json_object_iter_key()`. Using other keys will lead to segfaults. This function is used internally to implement :func:`json_object_foreach`. Example:: /* obj is a JSON object */ const char *key; json_t *value; void *iter = json_object_iter(obj); while(iter) { key = json_object_iter_key(iter); value = json_object_iter_value(iter); /* use key and value ... */ iter = json_object_iter_next(obj, iter); } .. versionadded:: 2.3
.. function:: void json_object_seed(size_t seed) Seed the hash function used in Jansson's hashtable implementation. The seed is used to randomize the hash function so that an attacker cannot control its output. If *seed* is 0, Jansson generates the seed itself by reading random data from the operating system's entropy sources. If no entropy sources are available, falls back to using a combination of the current timestamp (with microsecond precision if possible) and the process ID. If called at all, this function must be called before any calls to :func:`json_object()`, either explicit or implicit. If this function is not called by the user, the first call to :func:`json_object()` (either explicit or implicit) seeds the hash function. See :ref:`thread-safety` for notes on thread safety. If repeatable results are required, for e.g. unit tests, the hash function can be "unrandomized" by calling :func:`json_object_seed` with a constant value on program startup, e.g. ``json_object_seed(1)``. .. versionadded:: 2.6
Error reporting
Jansson uses a single struct type to pass error information to the
user. See sections :ref:`apiref-decoding`, :ref:`apiref-pack` and
:ref:`apiref-unpack` for functions that pass error information using
this struct.
.. type:: json_error_t .. member:: char text[] The error message (in UTF-8), or an empty string if a message is not available. The last byte of this array contains a numeric error code. Use :func:`json_error_code()` to extract this code. .. member:: char source[] Source of the error. This can be (a part of) the file name or a special identifier in angle brackets (e.g. ``<string>``). .. member:: int line The line number on which the error occurred. .. member:: int column The column on which the error occurred. Note that this is the *character column*, not the byte column, i.e. a multibyte UTF-8 character counts as one column. .. member:: int position The position in bytes from the start of the input. This is useful for debugging Unicode encoding problems.
The normal use of :type:`json_error_t` is to allocate it on the stack,
and pass a pointer to a function. Example:
int main() { json_t *json; json_error_t error; json = json_load_file("/path/to/file.json", 0, &error); if(!json) { /* the error variable contains error information */ } ... }
Also note that if the call succeeded (json != NULL in the above
example), the contents of error are generally left unspecified.
The decoding functions write to the position member also on
success. See :ref:`apiref-decoding` for more info.
All functions also accept NULL as the :type:`json_error_t` pointer,
in which case no error information is returned to the caller.
.. c:enum:: json_error_code An enumeration containing numeric error codes. The following errors are currently defined: ``json_error_unknown`` Unknown error. This should only be returned for non-errorneous :type:`json_error_t` structures. ``json_error_out_of_memory`` The library couldn’t allocate any heap memory. ``json_error_stack_overflow`` Nesting too deep. ``json_error_cannot_open_file`` Couldn’t open input file. ``json_error_invalid_argument`` A function argument was invalid. ``json_error_invalid_utf8`` The input string isn’t valid UTF-8. ``json_error_premature_end_of_input`` The input ended in the middle of a JSON value. ``json_error_end_of_input_expected`` There was some text after the end of a JSON value. See the ``JSON_DISABLE_EOF_CHECK`` flag. ``json_error_invalid_syntax`` JSON syntax error. ``json_error_invalid_format`` Invalid format string for packing or unpacking. ``json_error_wrong_type`` When packing or unpacking, the actual type of a value differed from the one specified in the format string. ``json_error_null_character`` A null character was detected in a JSON string. See the ``JSON_ALLOW_NUL`` flag. ``json_error_null_value`` When packing or unpacking, some key or value was ``NULL``. ``json_error_null_byte_in_key`` An object key would contain a null byte. Jansson can’t represent such keys; see :ref:`rfc-conformance`. ``json_error_duplicate_key`` Duplicate key in object. See the ``JSON_REJECT_DUPLICATES`` flag. ``json_error_numeric_overflow`` When converting a JSON number to a C numeric type, a numeric overflow was detected. ``json_error_item_not_found`` Key in object not found. ``json_error_index_out_of_range`` Array index is out of range. .. versionadded:: 2.11
.. function:: enum json_error_code json_error_code(const json_error_t *error) Returns the error code embedded in ``error->text``. .. versionadded:: 2.11
Encoding
This section describes the functions that can be used to encode
values to JSON. By default, only objects and arrays can be encoded
directly, since they are the only valid root values of a JSON text.
To encode any JSON value, use the JSON_ENCODE_ANY flag (see
below).
By default, the output has no newlines, and spaces are used between
array and object elements for a readable output. This behavior can be
altered by using the JSON_INDENT and JSON_COMPACT flags
described below. A newline is never appended to the end of the encoded
JSON data.
Each function takes a flags parameter that controls some aspects of
how the data is encoded. Its default value is 0. The following macros
can be ORed together to obtain flags.
JSON_INDENT(n)-
Pretty-print the result, using newlines between array and object
items, and indenting with n spaces. The valid range for n is
between 0 and 31 (inclusive), other values result in an undefined
output. IfJSON_INDENTis not used or n is 0, no newlines are
inserted between array and object items.The
JSON_MAX_INDENTconstant defines the maximum indentation
that can be used, and its value is 31... versionchanged:: 2.7 Added ``JSON_MAX_INDENT``. JSON_COMPACT- This flag enables a compact representation, i.e. sets the separator
between array and object items to","and between object keys
and values to":". Without this flag, the corresponding
separators are", "and": "for more readable output. JSON_ENSURE_ASCII- If this flag is used, the output is guaranteed to consist only of
ASCII characters. This is achieved by escaping all Unicode
characters outside the ASCII range. JSON_SORT_KEYS- If this flag is used, all the objects in output are sorted by key.
This is useful e.g. if two JSON texts are diffed or visually
compared. JSON_PRESERVE_ORDER-
Deprecated since version 2.8: Order of object keys
is always preserved.Prior to version 2.8: If this flag is used, object keys in the
output are sorted into the same order in which they were first
inserted to the object. For example, decoding a JSON text and then
encoding with this flag preserves the order of object keys. JSON_ENCODE_ANY-
Specifying this flag makes it possible to encode any JSON value on
its own. Without it, only objects and arrays can be passed as the
json value to the encoding functions.Note: Encoding any value may be useful in some scenarios, but
it’s generally discouraged as it violates strict compatibility with
RFC 4627. If you use this flag, don’t expect interoperability
with other JSON systems. JSON_ESCAPE_SLASH-
Escape the
/characters in strings with/. JSON_REAL_PRECISION(n)-
Output all real numbers with at most n digits of precision. The
valid range for n is between 0 and 31 (inclusive), and other
values result in an undefined behavior.By default, the precision is 17, to correctly and losslessly encode
all IEEE 754 double precision floating point numbers. JSON_EMBED-
If this flag is used, the opening and closing characters of the top-level
array (‘[‘, ‘]’) or object (‘{‘, ‘}’) are omitted during encoding. This
flag is useful when concatenating multiple arrays or objects into a stream.
These functions output UTF-8:
.. function:: char *json_dumps(const json_t *json, size_t flags) Returns the JSON representation of *json* as a string, or *NULL* on error. *flags* is described above. The return value must be freed by the caller using :func:`free()`. Note that if you have called :func:`json_set_alloc_funcs()` to override :func:`free()`, you should call your custom free function instead to free the return value.
.. function:: size_t json_dumpb(const json_t *json, char *buffer, size_t size, size_t flags) Writes the JSON representation of *json* to the *buffer* of *size* bytes. Returns the number of bytes that would be written or 0 on error. *flags* is described above. *buffer* is not null-terminated. This function never writes more than *size* bytes. If the return value is greater than *size*, the contents of the *buffer* are undefined. This behavior enables you to specify a NULL *buffer* to determine the length of the encoding. For example:: size_t size = json_dumpb(json, NULL, 0, 0); if (size == 0) return -1; char *buf = alloca(size); size = json_dumpb(json, buf, size, 0); .. versionadded:: 2.10
.. function:: int json_dumpf(const json_t *json, FILE *output, size_t flags) Write the JSON representation of *json* to the stream *output*. *flags* is described above. Returns 0 on success and -1 on error. If an error occurs, something may have already been written to *output*. In this case, the output is undefined and most likely not valid JSON.
.. function:: int json_dumpfd(const json_t *json, int output, size_t flags) Write the JSON representation of *json* to the stream *output*. *flags* is described above. Returns 0 on success and -1 on error. If an error occurs, something may have already been written to *output*. In this case, the output is undefined and most likely not valid JSON. It is important to note that this function can only succeed on stream file descriptors (such as SOCK_STREAM). Using this function on a non-stream file descriptor will result in undefined behavior. For non-stream file descriptors, see instead :func:`json_dumpb()`. This function requires POSIX and fails on all non-POSIX systems. .. versionadded:: 2.10
.. function:: int json_dump_file(const json_t *json, const char *path, size_t flags) Write the JSON representation of *json* to the file *path*. If *path* already exists, it is overwritten. *flags* is described above. Returns 0 on success and -1 on error.
.. type:: json_dump_callback_t A typedef for a function that's called by :func:`json_dump_callback()`:: typedef int (*json_dump_callback_t)(const char *buffer, size_t size, void *data); *buffer* points to a buffer containing a chunk of output, *size* is the length of the buffer, and *data* is the corresponding :func:`json_dump_callback()` argument passed through. *buffer* is guaranteed to be a valid UTF-8 string (i.e. multi-byte code unit sequences are preserved). *buffer* never contains embedded null bytes. On error, the function should return -1 to stop the encoding process. On success, it should return 0. .. versionadded:: 2.2
.. function:: int json_dump_callback(const json_t *json, json_dump_callback_t callback, void *data, size_t flags) Call *callback* repeatedly, passing a chunk of the JSON representation of *json* each time. *flags* is described above. Returns 0 on success and -1 on error. .. versionadded:: 2.2
Decoding
This section describes the functions that can be used to decode JSON
text to the Jansson representation of JSON data. The JSON
specification requires that a JSON text is either a serialized array
or object, and this requirement is also enforced with the following
functions. In other words, the top level value in the JSON text being
decoded must be either array or object. To decode any JSON value, use
the JSON_DECODE_ANY flag (see below).
See :ref:`rfc-conformance` for a discussion on Jansson’s conformance
to the JSON specification. It explains many design decisions that
affect especially the behavior of the decoder.
Each function takes a flags parameter that can be used to control
the behavior of the decoder. Its default value is 0. The following
macros can be ORed together to obtain flags.
JSON_REJECT_DUPLICATES-
Issue a decoding error if any JSON object in the input text
contains duplicate keys. Without this flag, the value of the last
occurrence of each key ends up in the result. Key equivalence is
checked byte-by-byte, without special Unicode comparison
algorithms. JSON_DECODE_ANY-
By default, the decoder expects an array or object as the input.
With this flag enabled, the decoder accepts any valid JSON value.Note: Decoding any value may be useful in some scenarios, but
it’s generally discouraged as it violates strict compatibility with
RFC 4627. If you use this flag, don’t expect interoperability
with other JSON systems. JSON_DISABLE_EOF_CHECK-
By default, the decoder expects that its whole input constitutes a
valid JSON text, and issues an error if there’s extra data after
the otherwise valid JSON input. With this flag enabled, the decoder
stops after decoding a valid JSON array or object, and thus allows
extra data after the JSON text.Normally, reading will stop when the last
]or}in the
JSON input is encountered. If bothJSON_DISABLE_EOF_CHECKand
JSON_DECODE_ANYflags are used, the decoder may read one extra
UTF-8 code unit (up to 4 bytes of input). For example, decoding
4truecorrectly decodes the integer 4, but also reads the
t. For this reason, if reading multiple consecutive values that
are not arrays or objects, they should be separated by at least one
whitespace character. JSON_DECODE_INT_AS_REAL-
JSON defines only one number type. Jansson distinguishes between
ints and reals. For more information see :ref:`real-vs-integer`.
With this flag enabled the decoder interprets all numbers as real
values. Integers that do not have an exact double representation
will silently result in a loss of precision. Integers that cause
a double overflow will cause an error. JSON_ALLOW_NUL-
Allow
u0000escape inside string values. This is a safety
measure; If you know your input can contain null bytes, use this
flag. If you don’t use this flag, you don’t have to worry about null
bytes inside strings unless you explicitly create themselves by
using e.g. :func:`json_stringn()` ors#format specifier for
:func:`json_pack()`.Object keys cannot have embedded null bytes even if this flag is
used.
Each function also takes an optional :type:`json_error_t` parameter
that is filled with error information if decoding fails. It’s also
updated on success; the number of bytes of input read is written to
its position field. This is especially useful when using
JSON_DISABLE_EOF_CHECK to read multiple consecutive JSON texts.
.. versionadded:: 2.3 Number of bytes of input read is written to the ``position`` field of the :type:`json_error_t` structure.
If no error or position information is needed, you can pass NULL.
.. function:: json_t *json_loads(const char *input, size_t flags, json_error_t *error) .. refcounting:: new Decodes the JSON string *input* and returns the array or object it contains, or *NULL* on error, in which case *error* is filled with information about the error. *flags* is described above.
.. function:: json_t *json_loadb(const char *buffer, size_t buflen, size_t flags, json_error_t *error) .. refcounting:: new Decodes the JSON string *buffer*, whose length is *buflen*, and returns the array or object it contains, or *NULL* on error, in which case *error* is filled with information about the error. This is similar to :func:`json_loads()` except that the string doesn't need to be null-terminated. *flags* is described above. .. versionadded:: 2.1
.. function:: json_t *json_loadf(FILE *input, size_t flags, json_error_t *error) .. refcounting:: new Decodes the JSON text in stream *input* and returns the array or object it contains, or *NULL* on error, in which case *error* is filled with information about the error. *flags* is described above. This function will start reading the input from whatever position the input file was in, without attempting to seek first. If an error occurs, the file position will be left indeterminate. On success, the file position will be at EOF, unless ``JSON_DISABLE_EOF_CHECK`` flag was used. In this case, the file position will be at the first character after the last ``]`` or ``}`` in the JSON input. This allows calling :func:`json_loadf()` on the same ``FILE`` object multiple times, if the input consists of consecutive JSON texts, possibly separated by whitespace.
.. function:: json_t *json_loadfd(int input, size_t flags, json_error_t *error) .. refcounting:: new Decodes the JSON text in stream *input* and returns the array or object it contains, or *NULL* on error, in which case *error* is filled with information about the error. *flags* is described above. This function will start reading the input from whatever position the input file descriptor was in, without attempting to seek first. If an error occurs, the file position will be left indeterminate. On success, the file position will be at EOF, unless ``JSON_DISABLE_EOF_CHECK`` flag was used. In this case, the file descriptor's position will be at the first character after the last ``]`` or ``}`` in the JSON input. This allows calling :func:`json_loadfd()` on the same file descriptor multiple times, if the input consists of consecutive JSON texts, possibly separated by whitespace. It is important to note that this function can only succeed on stream file descriptors (such as SOCK_STREAM). Using this function on a non-stream file descriptor will result in undefined behavior. For non-stream file descriptors, see instead :func:`json_loadb()`. In addition, please note that this function cannot be used on non-blocking file descriptors (such as a non-blocking socket). Using this function on non-blocking file descriptors has a high risk of data loss because it does not support resuming. This function requires POSIX and fails on all non-POSIX systems. .. versionadded:: 2.10
.. function:: json_t *json_load_file(const char *path, size_t flags, json_error_t *error) .. refcounting:: new Decodes the JSON text in file *path* and returns the array or object it contains, or *NULL* on error, in which case *error* is filled with information about the error. *flags* is described above.
.. type:: json_load_callback_t A typedef for a function that's called by :func:`json_load_callback()` to read a chunk of input data:: typedef size_t (*json_load_callback_t)(void *buffer, size_t buflen, void *data); *buffer* points to a buffer of *buflen* bytes, and *data* is the corresponding :func:`json_load_callback()` argument passed through. On success, the function should write at most *buflen* bytes to *buffer*, and return the number of bytes written; a returned value of 0 indicates that no data was produced and that the end of file has been reached. On error, the function should return ``(size_t)-1`` to abort the decoding process. In UTF-8, some code points are encoded as multi-byte sequences. The callback function doesn't need to worry about this, as Jansson handles it at a higher level. For example, you can safely read a fixed number of bytes from a network connection without having to care about code unit sequences broken apart by the chunk boundaries. .. versionadded:: 2.4
.. function:: json_t *json_load_callback(json_load_callback_t callback, void *data, size_t flags, json_error_t *error) .. refcounting:: new Decodes the JSON text produced by repeated calls to *callback*, and returns the array or object it contains, or *NULL* on error, in which case *error* is filled with information about the error. *data* is passed through to *callback* on each call. *flags* is described above. .. versionadded:: 2.4
Building Values
This section describes functions that help to create, or pack,
complex JSON values, especially nested objects and arrays. Value
building is based on a format string that is used to tell the
functions about the expected arguments.
For example, the format string "i" specifies a single integer
value, while the format string "[ssb]" or the equivalent "[s, s, specifies an array value with two strings and a boolean as its
b]"
items:
/* Create the JSON integer 42 */ json_pack("i", 42); /* Create the JSON array ["foo", "bar", true] */ json_pack("[ssb]", "foo", "bar", 1);
Here’s the full list of format specifiers. The type in parentheses
denotes the resulting JSON type, and the type in brackets (if any)
denotes the C type that is expected as the corresponding argument or
arguments.
s(string) [const char *]- Convert a null terminated UTF-8 string to a JSON string.
s?(string) [const char *]-
Like
s, but if the argument is NULL, output a JSON null
value. s*(string) [const char *]-
Like
s, but if the argument is NULL, do not output any value.
This format can only be used inside an object or an array. If used
inside an object, the corresponding key is additionally suppressed
when the value is omitted. See below for an example. s#(string) [const char *, int]-
Convert a UTF-8 buffer of a given length to a JSON string.
s%(string) [const char *, size_t]-
Like
s#but the length argument is of type :type:`size_t`. +[const char *]-
Like
s, but concatenate to the previous string. Only valid
afters,s#,+or+#. +#[const char *, int]-
Like
s#, but concatenate to the previous string. Only valid
afters,s#,+or+#. +%(string) [const char *, size_t]-
Like
+#but the length argument is of type :type:`size_t`. n(null)- Output a JSON null value. No argument is consumed.
b(boolean) [int]- Convert a C
intto JSON boolean value. Zero is converted
tofalseand non-zero totrue. i(integer) [int]- Convert a C
intto JSON integer. I(integer) [json_int_t]- Convert a C :type:`json_int_t` to JSON integer.
f(real) [double]- Convert a C
doubleto JSON real. o(any value) [json_t *]- Output any given JSON value as-is. If the value is added to an
array or object, the reference to the value passed toois
stolen by the container. O(any value) [json_t *]- Like
o, but the argument’s reference count is incremented.
This is useful if you pack into an array or object and want to
keep the reference for the JSON value consumed byOto
yourself. o?,O?(any value) [json_t *]-
Like
oandO, respectively, but if the argument is
NULL, output a JSON null value. o*,O*(any value) [json_t *]-
Like
oandO, respectively, but if the argument is
NULL, do not output any value. This format can only be used
inside an object or an array. If used inside an object, the
corresponding key is additionally suppressed. See below for an
example. [fmt](array)- Build an array with contents from the inner format string.
fmt
may contain objects and arrays, i.e. recursive value building is
supported. {fmt}(object)- Build an object with contents from the inner format string
fmt. The first, third, etc. format specifier represent a key,
and must be a string (sees,s#,+and+#above),
as object keys are always strings. The second, fourth, etc. format
specifier represent a value. Any value may be an object or array,
i.e. recursive value building is supported.
Whitespace, : and , are ignored.
.. function:: json_t *json_pack(const char *fmt, ...) .. refcounting:: new Build a new JSON value according to the format string *fmt*. For each format specifier (except for ``{}[]n``), one or more arguments are consumed and used to build the corresponding value. Returns *NULL* on error.
.. function:: json_t *json_pack_ex(json_error_t *error, size_t flags, const char *fmt, ...) json_t *json_vpack_ex(json_error_t *error, size_t flags, const char *fmt, va_list ap) .. refcounting:: new Like :func:`json_pack()`, but an in the case of an error, an error message is written to *error*, if it's not *NULL*. The *flags* parameter is currently unused and should be set to 0. As only the errors in format string (and out-of-memory errors) can be caught by the packer, these two functions are most likely only useful for debugging format strings.
More examples:
/* Build an empty JSON object */ json_pack("{}"); /* Build the JSON object {"foo": 42, "bar": 7} */ json_pack("{sisi}", "foo", 42, "bar", 7); /* Like above, ':', ',' and whitespace are ignored */ json_pack("{s:i, s:i}", "foo", 42, "bar", 7); /* Build the JSON array [[1, 2], {"cool": true}] */ json_pack("[[i,i],{s:b}]", 1, 2, "cool", 1); /* Build a string from a non-null terminated buffer */ char buffer[4] = {'t', 'e', 's', 't'}; json_pack("s#", buffer, 4); /* Concatenate strings together to build the JSON string "foobarbaz" */ json_pack("s++", "foo", "bar", "baz"); /* Create an empty object or array when optional members are missing */ json_pack("{s:s*,s:o*,s:O*}", "foo", NULL, "bar", NULL, "baz", NULL); json_pack("[s*,o*,O*]", NULL, NULL, NULL);
Parsing and Validating Values
This section describes functions that help to validate complex values
and extract, or unpack, data from them. Like :ref:`building values
<apiref-pack>`, this is also based on format strings.
While a JSON value is unpacked, the type specified in the format
string is checked to match that of the JSON value. This is the
validation part of the process. In addition to this, the unpacking
functions can also check that all items of arrays and objects are
unpacked. This check be enabled with the format specifier ! or by
using the flag JSON_STRICT. See below for details.
Here’s the full list of format specifiers. The type in parentheses
denotes the JSON type, and the type in brackets (if any) denotes the C
type whose address should be passed.
s(string) [const char *]- Convert a JSON string to a pointer to a null terminated UTF-8
string. The resulting string is extracted by using
:func:`json_string_value()` internally, so it exists as long as
there are still references to the corresponding JSON string. s%(string) [const char *, size_t *]-
Convert a JSON string to a pointer to a null terminated UTF-8
string and its length. n(null)- Expect a JSON null value. Nothing is extracted.
b(boolean) [int]- Convert a JSON boolean value to a C
int, so thattrue
is converted to 1 andfalseto 0. i(integer) [int]- Convert a JSON integer to C
int. I(integer) [json_int_t]- Convert a JSON integer to C :type:`json_int_t`.
f(real) [double]- Convert a JSON real to C
double. F(integer or real) [double]- Convert a JSON number (integer or real) to C
double. o(any value) [json_t *]- Store a JSON value with no conversion to a :type:`json_t` pointer.
O(any value) [json_t *]- Like
o, but the JSON value’s reference count is incremented.
Storage pointers should be initialized NULL before using unpack.
The caller is responsible for releasing all references incremented
by unpack, even when an error occurs. [fmt](array)- Convert each item in the JSON array according to the inner format
string.fmtmay contain objects and arrays, i.e. recursive
value extraction is supported. {fmt}(object)-
Convert each item in the JSON object according to the inner format
stringfmt. The first, third, etc. format specifier represent
a key, and must bes. The corresponding argument to unpack
functions is read as the object key. The second, fourth, etc.
format specifier represent a value and is written to the address
given as the corresponding argument. Note that every other
argument is read from and every other is written to.fmtmay contain objects and arrays as values, i.e. recursive
value extraction is supported... versionadded:: 2.3 Any ``s`` representing a key may be suffixed with a ``?`` to make the key optional. If the key is not found, nothing is extracted. See below for an example.
!- This special format specifier is used to enable the check that
all object and array items are accessed, on a per-value basis. It
must appear inside an array or object as the last format specifier
before the closing bracket or brace. To enable the check globally,
use theJSON_STRICTunpacking flag. *- This special format specifier is the opposite of
!. If the
JSON_STRICTflag is used,*can be used to disable the
strict check on a per-value basis. It must appear inside an array
or object as the last format specifier before the closing bracket
or brace.
Whitespace, : and , are ignored.
.. function:: int json_unpack(json_t *root, const char *fmt, ...) Validate and unpack the JSON value *root* according to the format string *fmt*. Returns 0 on success and -1 on failure.
.. function:: int json_unpack_ex(json_t *root, json_error_t *error, size_t flags, const char *fmt, ...) int json_vunpack_ex(json_t *root, json_error_t *error, size_t flags, const char *fmt, va_list ap) Validate and unpack the JSON value *root* according to the format string *fmt*. If an error occurs and *error* is not *NULL*, write error information to *error*. *flags* can be used to control the behaviour of the unpacker, see below for the flags. Returns 0 on success and -1 on failure.
Note
The first argument of all unpack functions is json_t *root
instead of const json_t *root, because the use of O format
specifier causes the reference count of root, or some value
reachable from root, to be increased. Furthermore, the o
format specifier may be used to extract a value as-is, which allows
modifying the structure or contents of a value reachable from
root.
If the O and o format specifiers are not used, it’s
perfectly safe to cast a const json_t * variable to plain
json_t * when used with these functions.
The following unpacking flags are available:
JSON_STRICT- Enable the extra validation step checking that all object and
array items are unpacked. This is equivalent to appending the
format specifier!to the end of every array and object in the
format string. JSON_VALIDATE_ONLY- Don’t extract any data, just validate the JSON value against the
given format string. Note that object keys must still be specified
after the format string.
Examples:
/* root is the JSON integer 42 */ int myint; json_unpack(root, "i", &myint); assert(myint == 42); /* root is the JSON object {"foo": "bar", "quux": true} */ const char *str; int boolean; json_unpack(root, "{s:s, s:b}", "foo", &str, "quux", &boolean); assert(strcmp(str, "bar") == 0 && boolean == 1); /* root is the JSON array [[1, 2], {"baz": null} */ json_error_t error; json_unpack_ex(root, &error, JSON_VALIDATE_ONLY, "[[i,i], {s:n}]", "baz"); /* returns 0 for validation success, nothing is extracted */ /* root is the JSON array [1, 2, 3, 4, 5] */ int myint1, myint2; json_unpack(root, "[ii!]", &myint1, &myint2); /* returns -1 for failed validation */ /* root is an empty JSON object */ int myint = 0, myint2 = 0, myint3 = 0; json_unpack(root, "{s?i, s?[ii]}", "foo", &myint1, "bar", &myint2, &myint3); /* myint1, myint2 or myint3 is no touched as "foo" and "bar" don't exist */
Equality
Testing for equality of two JSON values cannot, in general, be
achieved using the == operator. Equality in the terms of the
== operator states that the two :type:`json_t` pointers point to
exactly the same JSON value. However, two JSON values can be equal not
only if they are exactly the same value, but also if they have equal
«contents»:
- Two integer or real values are equal if their contained numeric
values are equal. An integer value is never equal to a real value,
though. - Two strings are equal if their contained UTF-8 strings are equal,
byte by byte. Unicode comparison algorithms are not implemented. - Two arrays are equal if they have the same number of elements and
each element in the first array is equal to the corresponding
element in the second array. - Two objects are equal if they have exactly the same keys and the
value for each key in the first object is equal to the value of the
corresponding key in the second object. - Two true, false or null values have no «contents», so they are equal
if their types are equal. (Because these values are singletons,
their equality can actually be tested with==.)
.. function:: int json_equal(json_t *value1, json_t *value2) Returns 1 if *value1* and *value2* are equal, as defined above. Returns 0 if they are unequal or one or both of the pointers are *NULL*.
Copying
Because of reference counting, passing JSON values around doesn’t
require copying them. But sometimes a fresh copy of a JSON value is
needed. For example, if you need to modify an array, but still want to
use the original afterwards, you should take a copy of it first.
Jansson supports two kinds of copying: shallow and deep. There is a
difference between these methods only for arrays and objects. Shallow
copying only copies the first level value (array or object) and uses
the same child values in the copied value. Deep copying makes a fresh
copy of the child values, too. Moreover, all the child values are deep
copied in a recursive fashion.
Copying objects preserves the insertion order of keys.
.. function:: json_t *json_copy(json_t *value) .. refcounting:: new Returns a shallow copy of *value*, or *NULL* on error.
.. function:: json_t *json_deep_copy(const json_t *value) .. refcounting:: new Returns a deep copy of *value*, or *NULL* on error.
Custom Memory Allocation
By default, Jansson uses :func:`malloc()` and :func:`free()` for
memory allocation. These functions can be overridden if custom
behavior is needed.
.. type:: json_malloc_t A typedef for a function pointer with :func:`malloc()`'s signature:: typedef void *(*json_malloc_t)(size_t);
.. type:: json_free_t A typedef for a function pointer with :func:`free()`'s signature:: typedef void (*json_free_t)(void *);
.. function:: void json_set_alloc_funcs(json_malloc_t malloc_fn, json_free_t free_fn) Use *malloc_fn* instead of :func:`malloc()` and *free_fn* instead of :func:`free()`. This function has to be called before any other Jansson's API functions to ensure that all memory operations use the same functions.
.. function:: void json_get_alloc_funcs(json_malloc_t *malloc_fn, json_free_t *free_fn) Fetch the current malloc_fn and free_fn used. Either parameter may be NULL. .. versionadded:: 2.8
Examples:
Circumvent problems with different CRT heaps on Windows by using
application’s :func:`malloc()` and :func:`free()`:
json_set_alloc_funcs(malloc, free);
Use the Boehm’s conservative garbage collector for memory
operations:
json_set_alloc_funcs(GC_malloc, GC_free);
Allow storing sensitive data (e.g. passwords or encryption keys) in
JSON structures by zeroing all memory when freed:
static void *secure_malloc(size_t size) { /* Store the memory area size in the beginning of the block */ void *ptr = malloc(size + 8); *((size_t *)ptr) = size; return ptr + 8; } static void secure_free(void *ptr) { size_t size; ptr -= 8; size = *((size_t *)ptr); guaranteed_memset(ptr, 0, size + 8); free(ptr); } int main() { json_set_alloc_funcs(secure_malloc, secure_free); /* ... */ }
For more information about the issues of storing sensitive data in
memory, see
http://www.dwheeler.com/secure-programs/Secure-Programs-HOWTO/protect-secrets.html.
The page also explains the :func:`guaranteed_memset()` function used
in the example and gives a sample implementation for it.
Fixed-Length keys
The Jansson API allows work with fixed-length keys. This can be useful in the following cases:
- The key is contained inside a buffer and is not null-terminated. In this case creating a new temporary buffer is not needed.
- The key contains U+0000 inside it.
List of API for fixed-length keys:
- :c:func:`json_object_getn`
- :c:func:`json_object_setn`
- :c:func:`json_object_setn_nocheck`
- :c:func:`json_object_setn_new`
- :c:func:`json_object_setn_new_nocheck`
- :c:func:`json_object_deln`
- :c:func:`json_object_iter_key_len`
- :c:func:`json_object_keylen_foreach`
- :c:func:`json_object_keylen_foreach_safe`
Examples:
Try to write a new function to get :c:struct:`json_t` by path separated by .
This requires:
- string iterator (no need to modify the input for better performance)
- API for working with fixed-size keys
The iterator:
struct string { const char *string; size_t length; }; size_t string_try_next(struct string *str, const char *delimiter) { str->string += strspn(str->string, delimiter); str->length = strcspn(str->string, delimiter); return str->length; } #define string_foreach(_string, _delimiter) for (; string_try_next(&(_string), _delimiter); (_string).string += (_string).length)
The function:
json_t *json_object_get_by_path(json_t *object, const char *path) { struct string str; json_t *out = object; str.string = path; string_foreach(str, ".") { out = json_object_getn(out, str.string, str.length); if (out == NULL) return NULL; } return out; }
And usage:
int main(void) { json_t *obj = json_pack("{s:{s:{s:b}}}", "a", "b", "c", 1); json_t *c = json_object_get_by_path(obj, "a.b.c"); assert(json_is_true(c)); json_decref(obj); }
Preliminaries¶
All declarations are in jansson.h, so it’s enough to
in each source file.
All constants are prefixed with JSON_ (except for those describing
the library version, prefixed with JANSSON_). Other identifiers
are prefixed with json_. Type names are suffixed with _t and
typedef’d so that the struct keyword need not be used.
Library Version¶
The Jansson version is of the form A.B.C, where A is the major
version, B is the minor version and C is the micro version. If the
micro version is zero, it’s omitted from the version string, i.e. the
version string is just A.B.
When a new release only fixes bugs and doesn’t add new features or
functionality, the micro version is incremented. When new features are
added in a backwards compatible way, the minor version is incremented
and the micro version is set to zero. When there are backwards
incompatible changes, the major version is incremented and others are
set to zero.
The following preprocessor constants specify the current version of
the library:
JANSSON_MAJOR_VERSION,JANSSON_MINOR_VERSION,JANSSON_MICRO_VERSION- Integers specifying the major, minor and micro versions,
respectively. JANSSON_VERSION- A string representation of the current version, e.g.
"1.2.1"or
"1.3". JANSSON_VERSION_HEX-
A 3-byte hexadecimal representation of the version, e.g.
0x010201for version 1.2.1 and0x010300for version 1.3.
This is useful in numeric comparisons, e.g.:#if JANSSON_VERSION_HEX >= 0x010300 /* Code specific to version 1.3 and above */ #endif
JANSSON_THREAD_SAFE_REFCOUNT- If this value is defined all read-only operations and reference counting in
Jansson are thread safe. This value is not defined for versions older than
2.11or when the compiler does not provide built-in atomic functions.
Value Representation¶
The JSON specification (RFC 4627) defines the following data types:
object, array, string, number, boolean, and null. JSON
types are used dynamically; arrays and objects can hold any other data
type, including themselves. For this reason, Jansson’s type system is
also dynamic in nature. There’s one C type to represent all JSON
values, and this structure knows the type of the JSON value it holds.
-
json_t¶ -
This data structure is used throughout the library to represent all
JSON values. It always contains the type of the JSON value it holds
and the value’s reference count. The rest depends on the type of the
value.
Objects of json_t are always used through a pointer. There
are APIs for querying the type, manipulating the reference count, and
for constructing and manipulating values of different types.
Unless noted otherwise, all API functions return an error value if an
error occurs. Depending on the function’s signature, the error value
is either NULL or -1. Invalid arguments or invalid input are
apparent sources for errors. Memory allocation and I/O operations may
also cause errors.
Type¶
-
enum
json_type¶ -
The type of a JSON value. The following members are defined:
JSON_OBJECTJSON_ARRAYJSON_STRINGJSON_INTEGERJSON_REALJSON_TRUEJSON_FALSEJSON_NULLThese correspond to JSON object, array, string, number, boolean and
null. A number is represented by either a value of the type
JSON_INTEGERor of the typeJSON_REAL. A true boolean value
is represented by a value of the typeJSON_TRUEand false by a
value of the typeJSON_FALSE.
-
int
json_typeof(const json_t *json)¶ -
Return the type of the JSON value (a
json_typecast to
int). json MUST NOT be NULL. This function is actually
implemented as a macro for speed.
-
json_is_object(const json_t *json)¶ -
json_is_array(const json_t *json)¶ -
json_is_string(const json_t *json)¶ -
json_is_integer(const json_t *json)¶ -
json_is_real(const json_t *json)¶ -
json_is_true(const json_t *json)¶ -
json_is_false(const json_t *json)¶ -
json_is_null(const json_t *json)¶ -
These functions (actually macros) return true (non-zero) for values
of the given type, and false (zero) for values of other types and
for NULL.
-
json_is_number(const json_t *json)¶ -
Returns true for values of types
JSON_INTEGERand
JSON_REAL, and false for other types and for NULL.
-
json_is_boolean(const json_t *json)¶ -
Returns true for types
JSON_TRUEandJSON_FALSE, and false
for values of other types and for NULL.
-
json_boolean_value(const json_t *json)¶ -
Alias of
json_is_true(), i.e. returns 1 forJSON_TRUE
and 0 otherwise.New in version 2.7.
Reference Count¶
The reference count is used to track whether a value is still in use
or not. When a value is created, it’s reference count is set to 1. If
a reference to a value is kept (e.g. a value is stored somewhere for
later use), its reference count is incremented, and when the value is
no longer needed, the reference count is decremented. When the
reference count drops to zero, there are no references left, and the
value can be destroyed.
-
json_t *
json_incref(json_t *json)¶ -
Increment the reference count of json if it’s not NULL.
Returns json.
-
void
json_decref(json_t *json)¶ -
Decrement the reference count of json. As soon as a call to
json_decref()drops the reference count to zero, the value
is destroyed and it can no longer be used.
Functions creating new JSON values set the reference count to 1. These
functions are said to return a new reference. Other functions
returning (existing) JSON values do not normally increase the
reference count. These functions are said to return a borrowed
reference. So, if the user will hold a reference to a value returned
as a borrowed reference, he must call json_incref(). As soon as
the value is no longer needed, json_decref() should be called
to release the reference.
Normally, all functions accepting a JSON value as an argument will
manage the reference, i.e. increase and decrease the reference count
as needed. However, some functions steal the reference, i.e. they
have the same result as if the user called json_decref() on
the argument right after calling the function. These functions are
suffixed with _new or have _new_ somewhere in their name.
For example, the following code creates a new JSON array and appends
an integer to it:
json_t *array, *integer; array = json_array(); integer = json_integer(42); json_array_append(array, integer); json_decref(integer);
Note how the caller has to release the reference to the integer value
by calling json_decref(). By using a reference stealing
function json_array_append_new() instead of
json_array_append(), the code becomes much simpler:
json_t *array = json_array(); json_array_append_new(array, json_integer(42));
In this case, the user doesn’t have to explicitly release the
reference to the integer value, as json_array_append_new()
steals the reference when appending the value to the array.
In the following sections it is clearly documented whether a function
will return a new or borrowed reference or steal a reference to its
argument.
Circular References¶
A circular reference is created when an object or an array is,
directly or indirectly, inserted inside itself. The direct case is
simple:
json_t *obj = json_object(); json_object_set(obj, "foo", obj);
Jansson will refuse to do this, and json_object_set() (and
all the other such functions for objects and arrays) will return with
an error status. The indirect case is the dangerous one:
json_t *arr1 = json_array(), *arr2 = json_array(); json_array_append(arr1, arr2); json_array_append(arr2, arr1);
In this example, the array arr2 is contained in the array
arr1, and vice versa. Jansson cannot check for this kind of
indirect circular references without a performance hit, so it’s up to
the user to avoid them.
If a circular reference is created, the memory consumed by the values
cannot be freed by json_decref(). The reference counts never
drops to zero because the values are keeping the references to each
other. Moreover, trying to encode the values with any of the encoding
functions will fail. The encoder detects circular references and
returns an error status.
Scope Dereferencing¶
New in version 2.9.
It is possible to use the json_auto_t type to automatically
dereference a value at the end of a scope. For example:
void function(void) { json_auto_t *value = NULL; value = json_string("foo"); /* json_decref(value) is automatically called. */ }
This feature is only available on GCC and Clang. So if your project
has a portability requirement for other compilers, you should avoid
this feature.
Additionally, as always, care should be taken when passing values to
functions that steal references.
True, False and Null¶
These three values are implemented as singletons, so the returned
pointers won’t change between invocations of these functions.
-
json_t *
json_true(void)¶ - Return value: New reference.
Returns the JSON true value.
-
json_t *
json_false(void)¶ - Return value: New reference.
Returns the JSON false value.
-
json_t *
json_boolean(val)¶ - Return value: New reference.
Returns JSON false if
valis zero, and JSON true otherwise.
This is a macro, and equivalent toval ? json_true() :.
json_false()New in version 2.4.
-
json_t *
json_null(void)¶ - Return value: New reference.
Returns the JSON null value.
String¶
Jansson uses UTF-8 as the character encoding. All JSON strings must be
valid UTF-8 (or ASCII, as it’s a subset of UTF-8). All Unicode
codepoints U+0000 through U+10FFFF are allowed, but you must use
length-aware functions if you wish to embed null bytes in strings.
-
json_t *
json_string(const char *value)¶ - Return value: New reference.
Returns a new JSON string, or NULL on error. value must be a
valid null terminated UTF-8 encoded Unicode string.
-
json_t *
json_stringn(const char *value, size_t len)¶ - Return value: New reference.
Like
json_string(), but with explicit length, so value may
contain null characters or not be null terminated.New in version 2.7.
-
json_t *
json_string_nocheck(const char *value)¶ - Return value: New reference.
Like
json_string(), but doesn’t check that value is valid
UTF-8. Use this function only if you are certain that this really
is the case (e.g. you have already checked it by other means).
-
json_t *
json_stringn_nocheck(const char *value, size_t len)¶ - Return value: New reference.
Like
json_string_nocheck(), but with explicit length, so
value may contain null characters or not be null terminated.New in version 2.7.
-
const char *
json_string_value(const json_t *string)¶ -
Returns the associated value of string as a null terminated UTF-8
encoded string, or NULL if string is not a JSON string.The returned value is read-only and must not be modified or freed by
the user. It is valid as long as string exists, i.e. as long as
its reference count has not dropped to zero.
-
size_t
json_string_length(const json_t *string)¶ -
Returns the length of string in its UTF-8 presentation, or zero
if string is not a JSON string.New in version 2.7.
-
int
json_string_set(json_t *string, const char *value)¶ -
Sets the associated value of string to value. value must be a
valid UTF-8 encoded Unicode string. Returns 0 on success and -1 on
error.
-
int
json_string_setn(json_t *string, const char *value, size_t len)¶ -
Like
json_string_set(), but with explicit length, so value
may contain null characters or not be null terminated.New in version 2.7.
-
int
json_string_set_nocheck(json_t *string, const char *value)¶ -
Like
json_string_set(), but doesn’t check that value is
valid UTF-8. Use this function only if you are certain that this
really is the case (e.g. you have already checked it by other
means).
-
int
json_string_setn_nocheck(json_t *string, const char *value, size_t len)¶ -
Like
json_string_set_nocheck(), but with explicit length,
so value may contain null characters or not be null terminated.New in version 2.7.
-
json_t *
json_sprintf(const char *format, …)¶ -
json_t *
json_vsprintf(const char *format, va_list ap)¶ - Return value: New reference.
Construct a JSON string from a format string and varargs, just like
printf().New in version 2.11.
Number¶
The JSON specification only contains one numeric type, “number”. The C
programming language has distinct types for integer and floating-point
numbers, so for practical reasons Jansson also has distinct types for
the two. They are called “integer” and “real”, respectively. For more
information, see RFC Conformance.
-
json_int_t¶ -
This is the C type that is used to store JSON integer values. It
represents the widest integer type available on your system. In
practice it’s just a typedef oflong longif your compiler
supports it, otherwiselong.Usually, you can safely use plain
intin place of
json_int_t, and the implicit C integer conversion handles the
rest. Only when you know that you need the full 64-bit range, you
should usejson_int_texplicitly.
JSON_INTEGER_IS_LONG_LONG-
This is a preprocessor variable that holds the value 1 if
json_int_tislong long, and 0 if it’slong. It
can be used as follows:#if JSON_INTEGER_IS_LONG_LONG /* Code specific for long long */ #else /* Code specific for long */ #endif
JSON_INTEGER_FORMAT-
This is a macro that expands to a
printf()conversion
specifier that corresponds tojson_int_t, without the
leading%sign, i.e. either"lld"or"ld". This macro
is required because the actual type ofjson_int_tcan be
eitherlongorlong long, andprintf()requires
different length modifiers for the two.Example:
json_int_t x = 123123123; printf("x is %" JSON_INTEGER_FORMAT "n", x);
-
json_t *
json_integer(json_int_t value)¶ - Return value: New reference.
Returns a new JSON integer, or NULL on error.
-
json_int_t
json_integer_value(const json_t *integer)¶ -
Returns the associated value of integer, or 0 if json is not a
JSON integer.
-
int
json_integer_set(const json_t *integer, json_int_t value)¶ -
Sets the associated value of integer to value. Returns 0 on
success and -1 if integer is not a JSON integer.
-
json_t *
json_real(double value)¶ - Return value: New reference.
Returns a new JSON real, or NULL on error.
-
double
json_real_value(const json_t *real)¶ -
Returns the associated value of real, or 0.0 if real is not a
JSON real.
-
int
json_real_set(const json_t *real, double value)¶ -
Sets the associated value of real to value. Returns 0 on
success and -1 if real is not a JSON real.
-
double
json_number_value(const json_t *json)¶ -
Returns the associated value of the JSON integer or JSON real
json, cast to double regardless of the actual type. If json is
neither JSON real nor JSON integer, 0.0 is returned.
Array¶
A JSON array is an ordered collection of other JSON values.
-
json_t *
json_array(void)¶ - Return value: New reference.
Returns a new JSON array, or NULL on error. Initially, the array
is empty.
-
size_t
json_array_size(const json_t *array)¶ -
Returns the number of elements in array, or 0 if array is NULL
or not a JSON array.
-
json_t *
json_array_get(const json_t *array, size_t index)¶ - Return value: Borrowed reference.
Returns the element in array at position index. The valid range
for index is from 0 to the return value of
json_array_size()minus 1. If array is not a JSON array,
if array is NULL, or if index is out of range, NULL is
returned.
-
int
json_array_set(json_t *array, size_t index, json_t *value)¶ -
Replaces the element in array at position index with value.
The valid range for index is from 0 to the return value of
json_array_size()minus 1. Returns 0 on success and -1 on
error.
-
int
json_array_set_new(json_t *array, size_t index, json_t *value)¶ -
Like
json_array_set()but steals the reference to value.
This is useful when value is newly created and not used after
the call.
-
int
json_array_append(json_t *array, json_t *value)¶ -
Appends value to the end of array, growing the size of array
by 1. Returns 0 on success and -1 on error.
-
int
json_array_append_new(json_t *array, json_t *value)¶ -
Like
json_array_append()but steals the reference to
value. This is useful when value is newly created and not used
after the call.
-
int
json_array_insert(json_t *array, size_t index, json_t *value)¶ -
Inserts value to array at position index, shifting the
elements at index and after it one position towards the end of
the array. Returns 0 on success and -1 on error.
-
int
json_array_insert_new(json_t *array, size_t index, json_t *value)¶ -
Like
json_array_insert()but steals the reference to
value. This is useful when value is newly created and not used
after the call.
-
int
json_array_remove(json_t *array, size_t index)¶ -
Removes the element in array at position index, shifting the
elements after index one position towards the start of the array.
Returns 0 on success and -1 on error. The reference count of the
removed value is decremented.
-
int
json_array_clear(json_t *array)¶ -
Removes all elements from array. Returns 0 on success and -1 on
error. The reference count of all removed values are decremented.
-
int
json_array_extend(json_t *array, json_t *other_array)¶ -
Appends all elements in other_array to the end of array.
Returns 0 on success and -1 on error.
-
json_array_foreach(array, index, value)¶ -
Iterate over every element of
array, running the block
of code that follows each time with the proper values set to
variablesindexandvalue, of typessize_tand
json_t *respectively. Example:/* array is a JSON array */ size_t index; json_t *value; json_array_foreach(array, index, value) { /* block of code that uses index and value */ }
The items are returned in increasing index order.
This macro expands to an ordinary
forstatement upon
preprocessing, so its performance is equivalent to that of
hand-written code using the array access functions.
The main advantage of this macro is that it abstracts
away the complexity, and makes for more concise and readable code.New in version 2.5.
Object¶
A JSON object is a dictionary of key-value pairs, where the key is a
Unicode string and the value is any JSON value.
Even though null bytes are allowed in string values, they are not
allowed in object keys.
-
json_t *
json_object(void)¶ - Return value: New reference.
Returns a new JSON object, or NULL on error. Initially, the
object is empty.
-
size_t
json_object_size(const json_t *object)¶ -
Returns the number of elements in object, or 0 if object is not
a JSON object.
-
json_t *
json_object_get(const json_t *object, const char *key)¶ - Return value: Borrowed reference.
Get a value corresponding to key from object. Returns NULL if
key is not found and on error.
-
int
json_object_set(json_t *object, const char *key, json_t *value)¶ -
Set the value of key to value in object. key must be a
valid null terminated UTF-8 encoded Unicode string. If there
already is a value for key, it is replaced by the new value.
Returns 0 on success and -1 on error.
-
int
json_object_set_nocheck(json_t *object, const char *key, json_t *value)¶ -
Like
json_object_set(), but doesn’t check that key is
valid UTF-8. Use this function only if you are certain that this
really is the case (e.g. you have already checked it by other
means).
-
int
json_object_set_new(json_t *object, const char *key, json_t *value)¶ -
Like
json_object_set()but steals the reference to
value. This is useful when value is newly created and not used
after the call.
-
int
json_object_set_new_nocheck(json_t *object, const char *key, json_t *value)¶ -
Like
json_object_set_new(), but doesn’t check that key is
valid UTF-8. Use this function only if you are certain that this
really is the case (e.g. you have already checked it by other
means).
-
int
json_object_del(json_t *object, const char *key)¶ -
Delete key from object if it exists. Returns 0 on success, or
-1 if key was not found. The reference count of the removed value
is decremented.
-
int
json_object_clear(json_t *object)¶ -
Remove all elements from object. Returns 0 on success and -1 if
object is not a JSON object. The reference count of all removed
values are decremented.
-
int
json_object_update(json_t *object, json_t *other)¶ -
Update object with the key-value pairs from other, overwriting
existing keys. Returns 0 on success or -1 on error.
-
int
json_object_update_existing(json_t *object, json_t *other)¶ -
Like
json_object_update(), but only the values of existing
keys are updated. No new keys are created. Returns 0 on success or
-1 on error.New in version 2.3.
-
int
json_object_update_missing(json_t *object, json_t *other)¶ -
Like
json_object_update(), but only new keys are created.
The value of any existing key is not changed. Returns 0 on success
or -1 on error.New in version 2.3.
-
json_object_foreach(object, key, value)¶ -
Iterate over every key-value pair of
object, running the block
of code that follows each time with the proper values set to
variableskeyandvalue, of typesconst char *and
json_t *respectively. Example:/* obj is a JSON object */ const char *key; json_t *value; json_object_foreach(obj, key, value) { /* block of code that uses key and value */ }
The items are returned in the order they were inserted to the
object.Note: It’s not safe to call
json_object_del(object, key)
during iteration. If you need to, use
json_object_foreach_safe()instead.This macro expands to an ordinary
forstatement upon
preprocessing, so its performance is equivalent to that of
hand-written iteration code using the object iteration protocol
(see below). The main advantage of this macro is that it abstracts
away the complexity behind iteration, and makes for more concise and
readable code.New in version 2.3.
-
json_object_foreach_safe(object, tmp, key, value)¶ -
Like
json_object_foreach(), but it’s safe to call
json_object_del(object, key)during iteration. You need to pass
an extravoid *parametertmpthat is used for temporary storage.New in version 2.8.
The following functions can be used to iterate through all key-value
pairs in an object. The items are returned in the order they were
inserted to the object.
-
void *
json_object_iter(json_t *object)¶ -
Returns an opaque iterator which can be used to iterate over all
key-value pairs in object, or NULL if object is empty.
-
void *
json_object_iter_at(json_t *object, const char *key)¶ -
Like
json_object_iter(), but returns an iterator to the
key-value pair in object whose key is equal to key, or NULL if
key is not found in object. Iterating forward to the end of
object only yields all key-value pairs of the object if key
happens to be the first key in the underlying hash table.
-
void *
json_object_iter_next(json_t *object, void *iter)¶ -
Returns an iterator pointing to the next key-value pair in object
after iter, or NULL if the whole object has been iterated
through.
-
const char *
json_object_iter_key(void *iter)¶ -
Extract the associated key from iter.
-
json_t *
json_object_iter_value(void *iter)¶ - Return value: Borrowed reference.
Extract the associated value from iter.
-
int
json_object_iter_set(json_t *object, void *iter, json_t *value)¶ -
Set the value of the key-value pair in object, that is pointed to
by iter, to value.
-
int
json_object_iter_set_new(json_t *object, void *iter, json_t *value)¶ -
Like
json_object_iter_set(), but steals the reference to
value. This is useful when value is newly created and not used
after the call.
-
void *
json_object_key_to_iter(const char *key)¶ -
Like
json_object_iter_at(), but much faster. Only works for
values returned byjson_object_iter_key(). Using other keys
will lead to segfaults. This function is used internally to
implementjson_object_foreach(). Example:/* obj is a JSON object */ const char *key; json_t *value; void *iter = json_object_iter(obj); while(iter) { key = json_object_iter_key(iter); value = json_object_iter_value(iter); /* use key and value ... */ iter = json_object_iter_next(obj, iter); }
New in version 2.3.
-
void
json_object_seed(size_t seed)¶ -
Seed the hash function used in Jansson’s hashtable implementation.
The seed is used to randomize the hash function so that an
attacker cannot control its output.If seed is 0, Jansson generates the seed itself by reading
random data from the operating system’s entropy sources. If no
entropy sources are available, falls back to using a combination
of the current timestamp (with microsecond precision if possible)
and the process ID.If called at all, this function must be called before any calls to
json_object(), either explicit or implicit. If this
function is not called by the user, the first call to
json_object()(either explicit or implicit) seeds the hash
function. See Thread safety for notes on thread
safety.If repeatable results are required, for e.g. unit tests, the hash
function can be “unrandomized” by callingjson_object_seed()
with a constant value on program startup, e.g.
json_object_seed(1).New in version 2.6.
Error reporting¶
Jansson uses a single struct type to pass error information to the
user. See sections Decoding, Building Values and
Parsing and Validating Values for functions that pass error information using
this struct.
-
json_error_t¶ -
-
char text[] -
The error message (in UTF-8), or an empty string if a message is
not available.The last byte of this array contains a numeric error code. Use
json_error_code()to extract this code.
-
char source[] -
Source of the error. This can be (a part of) the file name or a
special identifier in angle brackets (e.g.<string>).
-
int
line¶ -
The line number on which the error occurred.
-
int
column¶ -
The column on which the error occurred. Note that this is the
character column, not the byte column, i.e. a multibyte UTF-8
character counts as one column.
-
int
position¶ -
The position in bytes from the start of the input. This is
useful for debugging Unicode encoding problems.
-
The normal use of json_error_t is to allocate it on the stack,
and pass a pointer to a function. Example:
int main() { json_t *json; json_error_t error; json = json_load_file("/path/to/file.json", 0, &error); if(!json) { /* the error variable contains error information */ } ... }
Also note that if the call succeeded (json != NULL in the above
example), the contents of error are generally left unspecified.
The decoding functions write to the position member also on
success. See Decoding for more info.
All functions also accept NULL as the json_error_t pointer,
in which case no error information is returned to the caller.
-
enum
json_error_code¶ -
An enumeration containing numeric error codes. The following errors are
currently defined:json_error_unknownUnknown error. This should only be returned for non-errorneous
json_error_tstructures.json_error_out_of_memoryThe library couldn’t allocate any heap memory.
json_error_stack_overflowNesting too deep.
json_error_cannot_open_fileCouldn’t open input file.
json_error_invalid_argumentA function argument was invalid.
json_error_invalid_utf8The input string isn’t valid UTF-8.
json_error_premature_end_of_inputThe input ended in the middle of a JSON value.
json_error_end_of_input_expectedThere was some text after the end of a JSON value. See the
JSON_DISABLE_EOF_CHECKflag.json_error_invalid_syntaxJSON syntax error.
json_error_invalid_formatInvalid format string for packing or unpacking.
json_error_wrong_typeWhen packing or unpacking, the actual type of a value differed from the
one specified in the format string.json_error_null_characterA null character was detected in a JSON string. See the
JSON_ALLOW_NULflag.json_error_null_valueWhen packing or unpacking, some key or value was
NULL.json_error_null_byte_in_keyAn object key would contain a null byte. Jansson can’t represent such
keys; see RFC Conformance.json_error_duplicate_keyDuplicate key in object. See the
JSON_REJECT_DUPLICATESflag.json_error_numeric_overflowWhen converting a JSON number to a C numeric type, a numeric overflow
was detected.json_error_item_not_foundKey in object not found.
json_error_index_out_of_rangeArray index is out of range.
New in version 2.11.
-
enum json_error_code
json_error_code(const json_error_t *error) -
Returns the error code embedded in
error->text.New in version 2.11.
Encoding¶
This sections describes the functions that can be used to encode
values to JSON. By default, only objects and arrays can be encoded
directly, since they are the only valid root values of a JSON text.
To encode any JSON value, use the JSON_ENCODE_ANY flag (see
below).
By default, the output has no newlines, and spaces are used between
array and object elements for a readable output. This behavior can be
altered by using the JSON_INDENT and JSON_COMPACT flags
described below. A newline is never appended to the end of the encoded
JSON data.
Each function takes a flags parameter that controls some aspects of
how the data is encoded. Its default value is 0. The following macros
can be ORed together to obtain flags.
JSON_INDENT(n)-
Pretty-print the result, using newlines between array and object
items, and indenting with n spaces. The valid range for n is
between 0 and 31 (inclusive), other values result in an undefined
output. IfJSON_INDENTis not used or n is 0, no newlines are
inserted between array and object items.The
JSON_MAX_INDENTconstant defines the maximum indentation
that can be used, and its value is 31.Changed in version 2.7: Added
JSON_MAX_INDENT. JSON_COMPACT- This flag enables a compact representation, i.e. sets the separator
between array and object items to","and between object keys
and values to":". Without this flag, the corresponding
separators are", "and": "for more readable output. JSON_ENSURE_ASCII- If this flag is used, the output is guaranteed to consist only of
ASCII characters. This is achieved by escaping all Unicode
characters outside the ASCII range. JSON_SORT_KEYS- If this flag is used, all the objects in output are sorted by key.
This is useful e.g. if two JSON texts are diffed or visually
compared. JSON_PRESERVE_ORDER-
Deprecated since version 2.8: Order of object keys
is always preserved.Prior to version 2.8: If this flag is used, object keys in the
output are sorted into the same order in which they were first
inserted to the object. For example, decoding a JSON text and then
encoding with this flag preserves the order of object keys. JSON_ENCODE_ANY-
Specifying this flag makes it possible to encode any JSON value on
its own. Without it, only objects and arrays can be passed as the
json value to the encoding functions.Note: Encoding any value may be useful in some scenarios, but
it’s generally discouraged as it violates strict compatibility with
RFC 4627. If you use this flag, don’t expect interoperability
with other JSON systems.New in version 2.1.
JSON_ESCAPE_SLASH-
Escape the
/characters in strings with/.New in version 2.4.
JSON_REAL_PRECISION(n)-
Output all real numbers with at most n digits of precision. The
valid range for n is between 0 and 31 (inclusive), and other
values result in an undefined behavior.By default, the precision is 17, to correctly and losslessly encode
all IEEE 754 double precision floating point numbers.New in version 2.7.
JSON_EMBED-
If this flag is used, the opening and closing characters of the top-level
array (‘[‘, ‘]’) or object (‘{‘, ‘}’) are omitted during encoding. This
flag is useful when concatenating multiple arrays or objects into a stream.New in version 2.10.
These functions output UTF-8:
-
char *
json_dumps(const json_t *json, size_t flags)¶ -
Returns the JSON representation of json as a string, or NULL on
error. flags is described above. The return value must be freed
by the caller usingfree().
-
size_t
json_dumpb(const json_t *json, char *buffer, size_t size, size_t flags)¶ -
Writes the JSON representation of json to the buffer of
size bytes. Returns the number of bytes that would be written
or 0 on error. flags is described above. buffer is not
null-terminated.This function never writes more than size bytes. If the return
value is greater than size, the contents of the buffer are
undefined. This behavior enables you to specify a NULL buffer
to determine the length of the encoding. For example:size_t size = json_dumpb(json, NULL, 0, 0); if (size == 0) return -1; char *buf = alloca(size); size = json_dumpb(json, buf, size, 0);
New in version 2.10.
-
int
json_dumpf(const json_t *json, FILE *output, size_t flags)¶ -
Write the JSON representation of json to the stream output.
flags is described above. Returns 0 on success and -1 on error.
If an error occurs, something may have already been written to
output. In this case, the output is undefined and most likely not
valid JSON.
-
int
json_dumpfd(const json_t *json, int output, size_t flags)¶ -
Write the JSON representation of json to the stream output.
flags is described above. Returns 0 on success and -1 on error.
If an error occurs, something may have already been written to
output. In this case, the output is undefined and most likely not
valid JSON.It is important to note that this function can only succeed on stream
file descriptors (such as SOCK_STREAM). Using this function on a
non-stream file descriptor will result in undefined behavior. For
non-stream file descriptors, see insteadjson_dumpb().This function requires POSIX and fails on all non-POSIX systems.
New in version 2.10.
-
int
json_dump_file(const json_t *json, const char *path, size_t flags)¶ -
Write the JSON representation of json to the file path. If
path already exists, it is overwritten. flags is described
above. Returns 0 on success and -1 on error.
-
json_dump_callback_t¶ -
A typedef for a function that’s called by
json_dump_callback():typedef int (*json_dump_callback_t)(const char *buffer, size_t size, void *data);
buffer points to a buffer containing a chunk of output, size is
the length of the buffer, and data is the corresponding
json_dump_callback()argument passed through.buffer is guaranteed to be a valid UTF-8 string (i.e. multi-byte
code unit sequences are preserved). buffer never contains
embedded null bytes.On error, the function should return -1 to stop the encoding
process. On success, it should return 0.New in version 2.2.
-
int
json_dump_callback(const json_t *json, json_dump_callback_t callback, void *data, size_t flags)¶ -
Call callback repeatedly, passing a chunk of the JSON
representation of json each time. flags is described above.
Returns 0 on success and -1 on error.New in version 2.2.
Decoding¶
This sections describes the functions that can be used to decode JSON
text to the Jansson representation of JSON data. The JSON
specification requires that a JSON text is either a serialized array
or object, and this requirement is also enforced with the following
functions. In other words, the top level value in the JSON text being
decoded must be either array or object. To decode any JSON value, use
the JSON_DECODE_ANY flag (see below).
See RFC Conformance for a discussion on Jansson’s conformance
to the JSON specification. It explains many design decisions that
affect especially the behavior of the decoder.
Each function takes a flags parameter that can be used to control
the behavior of the decoder. Its default value is 0. The following
macros can be ORed together to obtain flags.
JSON_REJECT_DUPLICATES-
Issue a decoding error if any JSON object in the input text
contains duplicate keys. Without this flag, the value of the last
occurrence of each key ends up in the result. Key equivalence is
checked byte-by-byte, without special Unicode comparison
algorithms.New in version 2.1.
JSON_DECODE_ANY-
By default, the decoder expects an array or object as the input.
With this flag enabled, the decoder accepts any valid JSON value.Note: Decoding any value may be useful in some scenarios, but
it’s generally discouraged as it violates strict compatibility with
RFC 4627. If you use this flag, don’t expect interoperability
with other JSON systems.New in version 2.3.
JSON_DISABLE_EOF_CHECK-
By default, the decoder expects that its whole input constitutes a
valid JSON text, and issues an error if there’s extra data after
the otherwise valid JSON input. With this flag enabled, the decoder
stops after decoding a valid JSON array or object, and thus allows
extra data after the JSON text.Normally, reading will stop when the last
]or}in the
JSON input is encountered. If bothJSON_DISABLE_EOF_CHECKand
JSON_DECODE_ANYflags are used, the decoder may read one extra
UTF-8 code unit (up to 4 bytes of input). For example, decoding
4truecorrectly decodes the integer 4, but also reads the
t. For this reason, if reading multiple consecutive values that
are not arrays or objects, they should be separated by at least one
whitespace character.New in version 2.1.
JSON_DECODE_INT_AS_REAL-
JSON defines only one number type. Jansson distinguishes between
ints and reals. For more information see Real vs. Integer.
With this flag enabled the decoder interprets all numbers as real
values. Integers that do not have an exact double representation
will silently result in a loss of precision. Integers that cause
a double overflow will cause an error.New in version 2.5.
JSON_ALLOW_NUL-
Allow
u0000escape inside string values. This is a safety
measure; If you know your input can contain null bytes, use this
flag. If you don’t use this flag, you don’t have to worry about null
bytes inside strings unless you explicitly create themselves by
using e.g.json_stringn()ors#format specifier for
json_pack().Object keys cannot have embedded null bytes even if this flag is
used.New in version 2.6.
Each function also takes an optional json_error_t parameter
that is filled with error information if decoding fails. It’s also
updated on success; the number of bytes of input read is written to
its position field. This is especially useful when using
JSON_DISABLE_EOF_CHECK to read multiple consecutive JSON texts.
New in version 2.3: Number of bytes of input read is written to the position field
of the json_error_t structure.
If no error or position information is needed, you can pass NULL.
-
json_t *
json_loads(const char *input, size_t flags, json_error_t *error)¶ - Return value: New reference.
Decodes the JSON string input and returns the array or object it
contains, or NULL on error, in which case error is filled with
information about the error. flags is described above.
-
json_t *
json_loadb(const char *buffer, size_t buflen, size_t flags, json_error_t *error)¶ - Return value: New reference.
Decodes the JSON string buffer, whose length is buflen, and
returns the array or object it contains, or NULL on error, in
which case error is filled with information about the error. This
is similar tojson_loads()except that the string doesn’t
need to be null-terminated. flags is described above.New in version 2.1.
-
json_t *
json_loadf(FILE *input, size_t flags, json_error_t *error)¶ - Return value: New reference.
Decodes the JSON text in stream input and returns the array or
object it contains, or NULL on error, in which case error is
filled with information about the error. flags is described
above.This function will start reading the input from whatever position
the input file was in, without attempting to seek first. If an error
occurs, the file position will be left indeterminate. On success,
the file position will be at EOF, unlessJSON_DISABLE_EOF_CHECK
flag was used. In this case, the file position will be at the first
character after the last]or}in the JSON input. This
allows callingjson_loadf()on the sameFILEobject
multiple times, if the input consists of consecutive JSON texts,
possibly separated by whitespace.
-
json_t *
json_loadfd(int input, size_t flags, json_error_t *error)¶ - Return value: New reference.
Decodes the JSON text in stream input and returns the array or
object it contains, or NULL on error, in which case error is
filled with information about the error. flags is described
above.This function will start reading the input from whatever position
the input file descriptor was in, without attempting to seek first.
If an error occurs, the file position will be left indeterminate.
On success, the file position will be at EOF, unless
JSON_DISABLE_EOF_CHECKflag was used. In this case, the file
descriptor’s position will be at the first character after the last
]or}in the JSON input. This allows calling
json_loadfd()on the same file descriptor multiple times,
if the input consists of consecutive JSON texts, possibly separated
by whitespace.It is important to note that this function can only succeed on stream
file descriptors (such as SOCK_STREAM). Using this function on a
non-stream file descriptor will result in undefined behavior. For
non-stream file descriptors, see insteadjson_loadb().This function requires POSIX and fails on all non-POSIX systems.
New in version 2.10.
-
json_t *
json_load_file(const char *path, size_t flags, json_error_t *error)¶ - Return value: New reference.
Decodes the JSON text in file path and returns the array or
object it contains, or NULL on error, in which case error is
filled with information about the error. flags is described
above.
-
json_load_callback_t¶ -
A typedef for a function that’s called by
json_load_callback()to read a chunk of input data:typedef size_t (*json_load_callback_t)(void *buffer, size_t buflen, void *data);
buffer points to a buffer of buflen bytes, and data is the
correspondingjson_load_callback()argument passed through.On success, the function should write at most buflen bytes to
buffer, and return the number of bytes written; a returned value
of 0 indicates that no data was produced and that the end of file
has been reached. On error, the function should return
(size_t)-1to abort the decoding process.In UTF-8, some code points are encoded as multi-byte sequences. The
callback function doesn’t need to worry about this, as Jansson
handles it at a higher level. For example, you can safely read a
fixed number of bytes from a network connection without having to
care about code unit sequences broken apart by the chunk
boundaries.New in version 2.4.
-
json_t *
json_load_callback(json_load_callback_t callback, void *data, size_t flags, json_error_t *error)¶ - Return value: New reference.
Decodes the JSON text produced by repeated calls to callback, and
returns the array or object it contains, or NULL on error, in
which case error is filled with information about the error.
data is passed through to callback on each call. flags is
described above.New in version 2.4.
Building Values¶
This section describes functions that help to create, or pack,
complex JSON values, especially nested objects and arrays. Value
building is based on a format string that is used to tell the
functions about the expected arguments.
For example, the format string "i" specifies a single integer
value, while the format string "[ssb]" or the equivalent "[s, s, specifies an array value with two strings and a boolean as its
b]"
items:
/* Create the JSON integer 42 */ json_pack("i", 42); /* Create the JSON array ["foo", "bar", true] */ json_pack("[ssb]", "foo", "bar", 1);
Here’s the full list of format specifiers. The type in parentheses
denotes the resulting JSON type, and the type in brackets (if any)
denotes the C type that is expected as the corresponding argument or
arguments.
s(string) [const char *]- Convert a null terminated UTF-8 string to a JSON string.
s?(string) [const char *]-
Like
s, but if the argument is NULL, output a JSON null
value.New in version 2.8.
s*(string) [const char *]-
Like
s, but if the argument is NULL, do not output any value.
This format can only be used inside an object or an array. If used
inside an object, the corresponding key is additionally suppressed
when the value is omitted. See below for an example.New in version 2.11.
s#(string) [const char *, int]-
Convert a UTF-8 buffer of a given length to a JSON string.
New in version 2.5.
s%(string) [const char *, size_t]-
Like
s#but the length argument is of typesize_t.New in version 2.6.
+[const char *]-
Like
s, but concatenate to the previous string. Only valid
afters,s#,+or+#.New in version 2.5.
+#[const char *, int]-
Like
s#, but concatenate to the previous string. Only valid
afters,s#,+or+#.New in version 2.5.
+%(string) [const char *, size_t]-
Like
+#but the length argument is of typesize_t.New in version 2.6.
n(null)- Output a JSON null value. No argument is consumed.
b(boolean) [int]- Convert a C
intto JSON boolean value. Zero is converted
tofalseand non-zero totrue. i(integer) [int]- Convert a C
intto JSON integer. I(integer) [json_int_t]- Convert a C
json_int_tto JSON integer. f(real) [double]- Convert a C
doubleto JSON real. o(any value) [json_t *]- Output any given JSON value as-is. If the value is added to an
array or object, the reference to the value passed toois
stolen by the container. O(any value) [json_t *]- Like
o, but the argument’s reference count is incremented.
This is useful if you pack into an array or object and want to
keep the reference for the JSON value consumed byOto
yourself. o?,O?(any value) [json_t *]-
Like
oandO, respectively, but if the argument is
NULL, output a JSON null value.New in version 2.8.
o*,O*(any value) [json_t *]-
Like
oandO, respectively, but if the argument is
NULL, do not output any value. This format can only be used
inside an object or an array. If used inside an object, the
corresponding key is additionally suppressed. See below for an
example.New in version 2.11.
[fmt](array)- Build an array with contents from the inner format string.
fmt
may contain objects and arrays, i.e. recursive value building is
supported. {fmt}(object)- Build an object with contents from the inner format string
fmt. The first, third, etc. format specifier represent a key,
and must be a string (sees,s#,+and+#above),
as object keys are always strings. The second, fourth, etc. format
specifier represent a value. Any value may be an object or array,
i.e. recursive value building is supported.
Whitespace, : and , are ignored.
-
json_t *
json_pack(const char *fmt, …)¶ - Return value: New reference.
Build a new JSON value according to the format string fmt. For
each format specifier (except for{}[]n), one or more arguments
are consumed and used to build the corresponding value. Returns
NULL on error.
-
json_t *
json_pack_ex(json_error_t *error, size_t flags, const char *fmt, …)¶ -
json_t *
json_vpack_ex(json_error_t *error, size_t flags, const char *fmt, va_list ap)¶ - Return value: New reference.
Like
json_pack(), but an in the case of an error, an error
message is written to error, if it’s not NULL. The flags
parameter is currently unused and should be set to 0.As only the errors in format string (and out-of-memory errors) can
be caught by the packer, these two functions are most likely only
useful for debugging format strings.
More examples:
/* Build an empty JSON object */ json_pack("{}"); /* Build the JSON object {"foo": 42, "bar": 7} */ json_pack("{sisi}", "foo", 42, "bar", 7); /* Like above, ':', ',' and whitespace are ignored */ json_pack("{s:i, s:i}", "foo", 42, "bar", 7); /* Build the JSON array [[1, 2], {"cool": true}] */ json_pack("[[i,i],{s:b}]", 1, 2, "cool", 1); /* Build a string from a non-null terminated buffer */ char buffer[4] = {'t', 'e', 's', 't'}; json_pack("s#", buffer, 4); /* Concatenate strings together to build the JSON string "foobarbaz" */ json_pack("s++", "foo", "bar", "baz"); /* Create an empty object or array when optional members are missing */ json_pack("{s:s*,s:o*,s:O*}", "foo", NULL, "bar", NULL, "baz", NULL); json_pack("[s*,o*,O*]", NULL, NULL, NULL);
Parsing and Validating Values¶
This section describes functions that help to validate complex values
and extract, or unpack, data from them. Like building values, this is also based on format strings.
While a JSON value is unpacked, the type specified in the format
string is checked to match that of the JSON value. This is the
validation part of the process. In addition to this, the unpacking
functions can also check that all items of arrays and objects are
unpacked. This check be enabled with the format specifier ! or by
using the flag JSON_STRICT. See below for details.
Here’s the full list of format specifiers. The type in parentheses
denotes the JSON type, and the type in brackets (if any) denotes the C
type whose address should be passed.
s(string) [const char *]- Convert a JSON string to a pointer to a null terminated UTF-8
string. The resulting string is extracted by using
json_string_value()internally, so it exists as long as
there are still references to the corresponding JSON string. s%(string) [const char *, size_t *]-
Convert a JSON string to a pointer to a null terminated UTF-8
string and its length.New in version 2.6.
n(null)- Expect a JSON null value. Nothing is extracted.
b(boolean) [int]- Convert a JSON boolean value to a C
int, so thattrue
is converted to 1 andfalseto 0. i(integer) [int]- Convert a JSON integer to C
int. I(integer) [json_int_t]- Convert a JSON integer to C
json_int_t. f(real) [double]- Convert a JSON real to C
double. F(integer or real) [double]- Convert a JSON number (integer or real) to C
double. o(any value) [json_t *]- Store a JSON value with no conversion to a
json_tpointer. O(any value) [json_t *]- Like
o, but the JSON value’s reference count is incremented.
Storage pointers should be initialized NULL before using unpack.
The caller is responsible for releasing all references incremented
by unpack, even when an error occurs. [fmt](array)- Convert each item in the JSON array according to the inner format
string.fmtmay contain objects and arrays, i.e. recursive
value extraction is supported. {fmt}(object)-
Convert each item in the JSON object according to the inner format
stringfmt. The first, third, etc. format specifier represent
a key, and must bes. The corresponding argument to unpack
functions is read as the object key. The second fourth, etc.
format specifier represent a value and is written to the address
given as the corresponding argument. Note that every other
argument is read from and every other is written to.fmtmay contain objects and arrays as values, i.e. recursive
value extraction is supported.New in version 2.3: Any
srepresenting a key may be suffixed with a?to
make the key optional. If the key is not found, nothing is
extracted. See below for an example. !- This special format specifier is used to enable the check that
all object and array items are accessed, on a per-value basis. It
must appear inside an array or object as the last format specifier
before the closing bracket or brace. To enable the check globally,
use theJSON_STRICTunpacking flag. *- This special format specifier is the opposite of
!. If the
JSON_STRICTflag is used,*can be used to disable the
strict check on a per-value basis. It must appear inside an array
or object as the last format specifier before the closing bracket
or brace.
Whitespace, : and , are ignored.
-
int
json_unpack(json_t *root, const char *fmt, …)¶ -
Validate and unpack the JSON value root according to the format
string fmt. Returns 0 on success and -1 on failure.
-
int
json_unpack_ex(json_t *root, json_error_t *error, size_t flags, const char *fmt, …)¶ -
int
json_vunpack_ex(json_t *root, json_error_t *error, size_t flags, const char *fmt, va_list ap)¶ -
Validate and unpack the JSON value root according to the format
string fmt. If an error occurs and error is not NULL, write
error information to error. flags can be used to control the
behaviour of the unpacker, see below for the flags. Returns 0 on
success and -1 on failure.
Note
The first argument of all unpack functions is json_t *root
instead of const json_t *root, because the use of O format
specifier causes the reference count of root, or some value
reachable from root, to be increased. Furthermore, the o
format specifier may be used to extract a value as-is, which allows
modifying the structure or contents of a value reachable from
root.
If the O and o format specifiers are not used, it’s
perfectly safe to cast a const json_t * variable to plain
json_t * when used with these functions.
The following unpacking flags are available:
JSON_STRICT- Enable the extra validation step checking that all object and
array items are unpacked. This is equivalent to appending the
format specifier!to the end of every array and object in the
format string. JSON_VALIDATE_ONLY- Don’t extract any data, just validate the JSON value against the
given format string. Note that object keys must still be specified
after the format string.
Examples:
/* root is the JSON integer 42 */ int myint; json_unpack(root, "i", &myint); assert(myint == 42); /* root is the JSON object {"foo": "bar", "quux": true} */ const char *str; int boolean; json_unpack(root, "{s:s, s:b}", "foo", &str, "quux", &boolean); assert(strcmp(str, "bar") == 0 && boolean == 1); /* root is the JSON array [[1, 2], {"baz": null} */ json_error_t error; json_unpack_ex(root, &error, JSON_VALIDATE_ONLY, "[[i,i], {s:n}]", "baz"); /* returns 0 for validation success, nothing is extracted */ /* root is the JSON array [1, 2, 3, 4, 5] */ int myint1, myint2; json_unpack(root, "[ii!]", &myint1, &myint2); /* returns -1 for failed validation */ /* root is an empty JSON object */ int myint = 0, myint2 = 0, myint3 = 0; json_unpack(root, "{s?i, s?[ii]}", "foo", &myint1, "bar", &myint2, &myint3); /* myint1, myint2 or myint3 is no touched as "foo" and "bar" don't exist */
Equality¶
Testing for equality of two JSON values cannot, in general, be
achieved using the == operator. Equality in the terms of the
== operator states that the two json_t pointers point to
exactly the same JSON value. However, two JSON values can be equal not
only if they are exactly the same value, but also if they have equal
“contents”:
- Two integer or real values are equal if their contained numeric
values are equal. An integer value is never equal to a real value,
though. - Two strings are equal if their contained UTF-8 strings are equal,
byte by byte. Unicode comparison algorithms are not implemented. - Two arrays are equal if they have the same number of elements and
each element in the first array is equal to the corresponding
element in the second array. - Two objects are equal if they have exactly the same keys and the
value for each key in the first object is equal to the value of the
corresponding key in the second object. - Two true, false or null values have no “contents”, so they are equal
if their types are equal. (Because these values are singletons,
their equality can actually be tested with==.)
-
int
json_equal(json_t *value1, json_t *value2)¶ -
Returns 1 if value1 and value2 are equal, as defined above.
Returns 0 if they are unequal or one or both of the pointers are
NULL.
Copying¶
Because of reference counting, passing JSON values around doesn’t
require copying them. But sometimes a fresh copy of a JSON value is
needed. For example, if you need to modify an array, but still want to
use the original afterwards, you should take a copy of it first.
Jansson supports two kinds of copying: shallow and deep. There is a
difference between these methods only for arrays and objects. Shallow
copying only copies the first level value (array or object) and uses
the same child values in the copied value. Deep copying makes a fresh
copy of the child values, too. Moreover, all the child values are deep
copied in a recursive fashion.
Copying objects preserves the insertion order of keys.
-
json_t *
json_copy(json_t *value)¶ - Return value: New reference.
Returns a shallow copy of value, or NULL on error.
-
json_t *
json_deep_copy(const json_t *value)¶ - Return value: New reference.
Returns a deep copy of value, or NULL on error.
Custom Memory Allocation¶
By default, Jansson uses malloc() and free() for
memory allocation. These functions can be overridden if custom
behavior is needed.
-
json_malloc_t¶ -
A typedef for a function pointer with
malloc()’s
signature:typedef void *(*json_malloc_t)(size_t);
-
json_free_t¶ -
A typedef for a function pointer with
free()’s
signature:typedef void (*json_free_t)(void *);
-
void
json_set_alloc_funcs(json_malloc_t malloc_fn, json_free_t free_fn)¶ -
Use malloc_fn instead of
malloc()and free_fn instead
offree(). This function has to be called before any other
Jansson’s API functions to ensure that all memory operations use
the same functions.
-
void
json_get_alloc_funcs(json_malloc_t *malloc_fn, json_free_t *free_fn)¶ -
Fetch the current malloc_fn and free_fn used. Either parameter
may be NULL.New in version 2.8.
Examples:
Circumvent problems with different CRT heaps on Windows by using
application’s malloc() and free():
json_set_alloc_funcs(malloc, free);
Use the Boehm’s conservative garbage collector for memory
operations:
json_set_alloc_funcs(GC_malloc, GC_free);
Allow storing sensitive data (e.g. passwords or encryption keys) in
JSON structures by zeroing all memory when freed:
static void *secure_malloc(size_t size) { /* Store the memory area size in the beginning of the block */ void *ptr = malloc(size + 8); *((size_t *)ptr) = size; return ptr + 8; } static void secure_free(void *ptr) { size_t size; ptr -= 8; size = *((size_t *)ptr); guaranteed_memset(ptr, 0, size + 8); free(ptr); } int main() { json_set_alloc_funcs(secure_malloc, secure_free); /* ... */ }
For more information about the issues of storing sensitive data in
memory, see
http://www.dwheeler.com/secure-programs/Secure-Programs-HOWTO/protect-secrets.html.
The page also explains the guaranteed_memset() function used
in the example and gives a sample implementation for it.
Let’s say that you’re building a JSON API with Go. And in some of the handlers — probably as part of a POST or PUT request — you want to read a JSON object from the request body and assign it to a struct in your code.
After a bit of research, there’s a good chance that you’ll end up with some code that looks similar to the personCreate handler here:
package main
import (
"encoding/json"
"fmt"
"log"
"net/http"
)
type Person struct {
Name string
Age int
}
func personCreate(w http.ResponseWriter, r *http.Request) {
// Declare a new Person struct.
var p Person
// Try to decode the request body into the struct. If there is an error,
// respond to the client with the error message and a 400 status code.
err := json.NewDecoder(r.Body).Decode(&p)
if err != nil {
http.Error(w, err.Error(), http.StatusBadRequest)
return
}
// Do something with the Person struct...
fmt.Fprintf(w, "Person: %+v", p)
}
func main() {
mux := http.NewServeMux()
mux.HandleFunc("/person/create", personCreate)
err := http.ListenAndServe(":4000", mux)
log.Fatal(err)
}
If you’re putting together a quick prototype, or building an API for personal/internal use only, then the code in the personCreate handler is probably OK.
But if you’re building an API for public use in production then there are a few issues with this to be aware of, and things that can be improved.
-
Not all errors returned by
Decode()are caused by a bad request from the client. Specifically,Decode()can return ajson.InvalidUnmarshalErrorerror — which is caused by an unmarshalable target destination being passed toDecode(). If that happens, then it indicates a problem with your application — not the client request — so really the error should be logged and a500 Internal Server Errorresponse sent to the client instead. -
The error messages returned by
Decode()aren’t ideal for sending to a client. Some are arguably too detailed and expose information about the underlying program (like"json: cannot unmarshal number into Go struct field Person.Name of type string"). Others aren’t descriptive enough (like"unexpected EOF") and some are just plain confusing (like"invalid character 'A' looking for beginning of object key string"). There also isn’t consistency in the formatting or language used. -
A client can include extra unexpected fields in their JSON, and these fields will be silently ignored without the client receiving any error. We can fix this by using the decoder’s
DisallowUnknownFields()method. -
There’s no upper limit on the size of the request body that will be read by the
Decode()method. Limiting this would help prevent our server resources being wasted if a malcious client sends a very large request body, and it’s something we can easily do by using thehttp.MaxBytesReader()function. -
There’s no check for a
Content-Type: application/jsonheader in the request. Of course, this header may not always be present, and mistakes and malicious clients mean that it isn’t a guarantee of the actual content type. But checking for an incorrectContent-Typeheader would allow us to ‘fail fast’ and send a helpful error message without spending unnecessary resources on parsing the body. -
The decoder that we create with
json.NewDecoder()is designed to decode streams of JSON objects and considers a request body like'{"Name": "Bob"}{"Name": "Carol": "Age": 54}'or'{"Name": "Dave"}{}'to be valid. But in the code above only the first JSON object in the request body will actually be parsed. So if the client sends multiple JSON objects in the request body, we want to alert them to the fact that only a single object is supported.There are two ways to achieve this. We can either call the decoder’s
Decode()method for a second time and make sure that it returns anio.EOFerror (if it does, then we know there are not any additional JSON objects or other data in the request body). Or we could avoid usingDecode()altogether and read the body into a byte slice and pass it tojson.Unmarshal(), which would return an error if the body contains multiple JSON objects. The downside of usingjson.Unmarshal()is that there is no way to disallow extra unexpected fields in the JSON, so we can’t address point 3 above.
An Improved Handler
Let’s implement an alternative version of the personCreate handler which addresses all of these issues.
You’ll notice here that we’re using the new errors.Is() and errors.As() functions, which have been introduced in Go 1.13, to help intercept the errors from Decode().
package main
import (
"encoding/json"
"errors"
"fmt"
"io"
"log"
"net/http"
"strings"
"github.com/golang/gddo/httputil/header"
)
type Person struct {
Name string
Age int
}
func personCreate(w http.ResponseWriter, r *http.Request) {
// If the Content-Type header is present, check that it has the value
// application/json. Note that we are using the gddo/httputil/header
// package to parse and extract the value here, so the check works
// even if the client includes additional charset or boundary
// information in the header.
if r.Header.Get("Content-Type") != "" {
value, _ := header.ParseValueAndParams(r.Header, "Content-Type")
if value != "application/json" {
msg := "Content-Type header is not application/json"
http.Error(w, msg, http.StatusUnsupportedMediaType)
return
}
}
// Use http.MaxBytesReader to enforce a maximum read of 1MB from the
// response body. A request body larger than that will now result in
// Decode() returning a "http: request body too large" error.
r.Body = http.MaxBytesReader(w, r.Body, 1048576)
// Setup the decoder and call the DisallowUnknownFields() method on it.
// This will cause Decode() to return a "json: unknown field ..." error
// if it encounters any extra unexpected fields in the JSON. Strictly
// speaking, it returns an error for "keys which do not match any
// non-ignored, exported fields in the destination".
dec := json.NewDecoder(r.Body)
dec.DisallowUnknownFields()
var p Person
err := dec.Decode(&p)
if err != nil {
var syntaxError *json.SyntaxError
var unmarshalTypeError *json.UnmarshalTypeError
switch {
// Catch any syntax errors in the JSON and send an error message
// which interpolates the location of the problem to make it
// easier for the client to fix.
case errors.As(err, &syntaxError):
msg := fmt.Sprintf("Request body contains badly-formed JSON (at position %d)", syntaxError.Offset)
http.Error(w, msg, http.StatusBadRequest)
// In some circumstances Decode() may also return an
// io.ErrUnexpectedEOF error for syntax errors in the JSON. There
// is an open issue regarding this at
// https://github.com/golang/go/issues/25956.
case errors.Is(err, io.ErrUnexpectedEOF):
msg := fmt.Sprintf("Request body contains badly-formed JSON")
http.Error(w, msg, http.StatusBadRequest)
// Catch any type errors, like trying to assign a string in the
// JSON request body to a int field in our Person struct. We can
// interpolate the relevant field name and position into the error
// message to make it easier for the client to fix.
case errors.As(err, &unmarshalTypeError):
msg := fmt.Sprintf("Request body contains an invalid value for the %q field (at position %d)", unmarshalTypeError.Field, unmarshalTypeError.Offset)
http.Error(w, msg, http.StatusBadRequest)
// Catch the error caused by extra unexpected fields in the request
// body. We extract the field name from the error message and
// interpolate it in our custom error message. There is an open
// issue at https://github.com/golang/go/issues/29035 regarding
// turning this into a sentinel error.
case strings.HasPrefix(err.Error(), "json: unknown field "):
fieldName := strings.TrimPrefix(err.Error(), "json: unknown field ")
msg := fmt.Sprintf("Request body contains unknown field %s", fieldName)
http.Error(w, msg, http.StatusBadRequest)
// An io.EOF error is returned by Decode() if the request body is
// empty.
case errors.Is(err, io.EOF):
msg := "Request body must not be empty"
http.Error(w, msg, http.StatusBadRequest)
// Catch the error caused by the request body being too large. Again
// there is an open issue regarding turning this into a sentinel
// error at https://github.com/golang/go/issues/30715.
case err.Error() == "http: request body too large":
msg := "Request body must not be larger than 1MB"
http.Error(w, msg, http.StatusRequestEntityTooLarge)
// Otherwise default to logging the error and sending a 500 Internal
// Server Error response.
default:
log.Print(err.Error())
http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
}
return
}
// Call decode again, using a pointer to an empty anonymous struct as
// the destination. If the request body only contained a single JSON
// object this will return an io.EOF error. So if we get anything else,
// we know that there is additional data in the request body.
err = dec.Decode(&struct{}{})
if err != io.EOF {
msg := "Request body must only contain a single JSON object"
http.Error(w, msg, http.StatusBadRequest)
return
}
fmt.Fprintf(w, "Person: %+v", p)
}
func main() {
mux := http.NewServeMux()
mux.HandleFunc("/person/create", personCreate)
err := http.ListenAndServe(":4000", mux)
log.Fatal(err)
}
The clear downside here is that this code is a lot more verbose, and IMO, a little bit ugly. Things aren’t helped by the fact that there are quite a few open issues with json/encoding which are on hold pending a wider review of the package.
But from a security and client perspective it’s a lot better 😊
The handler is now stricter about the content it will accept; we’re reducing the amount of server resources used unnecessarily; and the client gets clear and consistent error messages that provide a decent amount of information without over-sharing.
As a side note, you might have noticed that the json/encoding package contains some other error types (like json.UnmarshalFieldError) which aren’t checked in the code above — but these have been deprecated and not used by the current version of Go.
Making a Helper Function
If you’ve got a few handlers that need to to process JSON request bodies, you probably don’t want to repeat this code in all of them.
A solution which I’ve found works well is to create a decodeJSONBody() helper function, and have this return a custom malformedRequest error type which wraps the errors and relevant status codes.
For example:
package main
import (
"encoding/json"
"errors"
"fmt"
"io"
"net/http"
"strings"
"github.com/golang/gddo/httputil/header"
)
type malformedRequest struct {
status int
msg string
}
func (mr *malformedRequest) Error() string {
return mr.msg
}
func decodeJSONBody(w http.ResponseWriter, r *http.Request, dst interface{}) error {
if r.Header.Get("Content-Type") != "" {
value, _ := header.ParseValueAndParams(r.Header, "Content-Type")
if value != "application/json" {
msg := "Content-Type header is not application/json"
return &malformedRequest{status: http.StatusUnsupportedMediaType, msg: msg}
}
}
r.Body = http.MaxBytesReader(w, r.Body, 1048576)
dec := json.NewDecoder(r.Body)
dec.DisallowUnknownFields()
err := dec.Decode(&dst)
if err != nil {
var syntaxError *json.SyntaxError
var unmarshalTypeError *json.UnmarshalTypeError
switch {
case errors.As(err, &syntaxError):
msg := fmt.Sprintf("Request body contains badly-formed JSON (at position %d)", syntaxError.Offset)
return &malformedRequest{status: http.StatusBadRequest, msg: msg}
case errors.Is(err, io.ErrUnexpectedEOF):
msg := fmt.Sprintf("Request body contains badly-formed JSON")
return &malformedRequest{status: http.StatusBadRequest, msg: msg}
case errors.As(err, &unmarshalTypeError):
msg := fmt.Sprintf("Request body contains an invalid value for the %q field (at position %d)", unmarshalTypeError.Field, unmarshalTypeError.Offset)
return &malformedRequest{status: http.StatusBadRequest, msg: msg}
case strings.HasPrefix(err.Error(), "json: unknown field "):
fieldName := strings.TrimPrefix(err.Error(), "json: unknown field ")
msg := fmt.Sprintf("Request body contains unknown field %s", fieldName)
return &malformedRequest{status: http.StatusBadRequest, msg: msg}
case errors.Is(err, io.EOF):
msg := "Request body must not be empty"
return &malformedRequest{status: http.StatusBadRequest, msg: msg}
case err.Error() == "http: request body too large":
msg := "Request body must not be larger than 1MB"
return &malformedRequest{status: http.StatusRequestEntityTooLarge, msg: msg}
default:
return err
}
}
err = dec.Decode(&struct{}{})
if err != io.EOF {
msg := "Request body must only contain a single JSON object"
return &malformedRequest{status: http.StatusBadRequest, msg: msg}
}
return nil
}
Once that’s written, the code in your handlers can be kept really nice and compact:
package main
import (
"errors"
"fmt"
"log"
"net/http"
)
type Person struct {
Name string
Age int
}
func personCreate(w http.ResponseWriter, r *http.Request) {
var p Person
err := decodeJSONBody(w, r, &p)
if err != nil {
var mr *malformedRequest
if errors.As(err, &mr) {
http.Error(w, mr.msg, mr.status)
} else {
log.Print(err.Error())
http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
}
return
}
fmt.Fprintf(w, "Person: %+v", p)
}
func main() {
mux := http.NewServeMux()
mux.HandleFunc("/person/create", personCreate)
log.Print("Starting server on :4000...")
err := http.ListenAndServe(":4000", mux)
log.Fatal(err)
}
(PHP 5 >= 5.3.0, PHP 7, PHP 
json_last_error — Returns the last error occurred
Description
json_last_error(): int
Parameters
This function has no parameters.
Return Values
Returns an integer, the value can be one of the following
constants:
| Constant | Meaning | Availability |
|---|---|---|
JSON_ERROR_NONE |
No error has occurred | |
JSON_ERROR_DEPTH |
The maximum stack depth has been exceeded | |
JSON_ERROR_STATE_MISMATCH |
Invalid or malformed JSON | |
JSON_ERROR_CTRL_CHAR |
Control character error, possibly incorrectly encoded | |
JSON_ERROR_SYNTAX |
Syntax error | |
JSON_ERROR_UTF8 |
Malformed UTF-8 characters, possibly incorrectly encoded | |
JSON_ERROR_RECURSION |
One or more recursive references in the value to be encoded | |
JSON_ERROR_INF_OR_NAN |
One or moreNANor INFvalues in the value to be encoded |
|
JSON_ERROR_UNSUPPORTED_TYPE |
A value of a type that cannot be encoded was given | |
JSON_ERROR_INVALID_PROPERTY_NAME |
A property name that cannot be encoded was given | |
JSON_ERROR_UTF16 |
Malformed UTF-16 characters, possibly incorrectly encoded |
Examples
Example #1 json_last_error() example
<?php
// A valid json string
$json[] = '{"Organization": "PHP Documentation Team"}';// An invalid json string which will cause an syntax
// error, in this case we used ' instead of " for quotation
$json[] = "{'Organization': 'PHP Documentation Team'}";
foreach (
$json as $string) {
echo 'Decoding: ' . $string;
json_decode($string);
switch (
json_last_error()) {
case JSON_ERROR_NONE:
echo ' - No errors';
break;
case JSON_ERROR_DEPTH:
echo ' - Maximum stack depth exceeded';
break;
case JSON_ERROR_STATE_MISMATCH:
echo ' - Underflow or the modes mismatch';
break;
case JSON_ERROR_CTRL_CHAR:
echo ' - Unexpected control character found';
break;
case JSON_ERROR_SYNTAX:
echo ' - Syntax error, malformed JSON';
break;
case JSON_ERROR_UTF8:
echo ' - Malformed UTF-8 characters, possibly incorrectly encoded';
break;
default:
echo ' - Unknown error';
break;
}
echo
PHP_EOL;
}
?>
The above example will output:
Decoding: {"Organization": "PHP Documentation Team"} - No errors
Decoding: {'Organization': 'PHP Documentation Team'} - Syntax error, malformed JSON
Example #2 json_last_error() with json_encode()
<?php
// An invalid UTF8 sequence
$text = "xB1x31";$json = json_encode($text);
$error = json_last_error();var_dump($json, $error === JSON_ERROR_UTF8);
?>
The above example will output:
string(4) "null" bool(true)
Example #3 json_last_error() and JSON_THROW_ON_ERROR
<?php
// An invalid UTF8 sequence which causes JSON_ERROR_UTF8
json_encode("xB1x31");// The following does not cause a JSON error
json_encode('okay', JSON_THROW_ON_ERROR);// The global error state has not been changed by the former json_encode()
var_dump(json_last_error() === JSON_ERROR_UTF8);
?>
The above example will output:
See Also
- json_last_error_msg() — Returns the error string of the last json_encode() or json_decode() call
- json_decode() — Decodes a JSON string
- json_encode() — Returns the JSON representation of a value
jimmetry at gmail dot com ¶
11 years ago
While this can obviously change between versions, the current error codes are as follows:
0 = JSON_ERROR_NONE
1 = JSON_ERROR_DEPTH
2 = JSON_ERROR_STATE_MISMATCH
3 = JSON_ERROR_CTRL_CHAR
4 = JSON_ERROR_SYNTAX
5 = JSON_ERROR_UTF8
I'm only posting these for people who may be trying to understand why specific JSON files are not being decoded. Please do not hard-code these numbers into an error handler routine.
praveenscience at gmail dot com ¶
8 years ago
I used this simple script, flicked from StackOverflow to escape from the function failing:
<?php
function utf8ize($d) {
if (is_array($d)) {
foreach ($d as $k => $v) {
$d[$k] = utf8ize($v);
}
} else if (is_string ($d)) {
return utf8_encode($d);
}
return $d;
}
?>
Cheers,
Praveen Kumar!
msxcms at bmforum dot com ¶
5 years ago
use this code with mb_convert_encoding, you can json_encode some corrupt UTF-8 chars
function safe_json_encode($value, $options = 0, $depth = 512) {
$encoded = json_encode($value, $options, $depth);
if ($encoded === false && $value && json_last_error() == JSON_ERROR_UTF8) {
$encoded = json_encode(utf8ize($value), $options, $depth);
}
return $encoded;
}
function utf8ize($mixed) {
if (is_array($mixed)) {
foreach ($mixed as $key => $value) {
$mixed[$key] = utf8ize($value);
}
} elseif (is_string($mixed)) {
return mb_convert_encoding($mixed, "UTF-8", "UTF-8");
}
return $mixed;
}
hemono at gmail dot com ¶
7 years ago
when json_decode a empty string, PHP7 will trigger an Syntax error:
<?php
json_decode("");
var_dump(json_last_error(), json_last_error_msg());// PHP 7
int(4)
string(12) "Syntax error"// PHP 5
int(0)
string(8) "No error"
George Dimitriadis ¶
6 years ago
Just adding this note since I had to code this for the actual values reference.
<?phpecho JSON_ERROR_NONE . ' JSON_ERROR_NONE' . '<br />';
echo JSON_ERROR_DEPTH . ' JSON_ERROR_DEPTH' . '<br />';
echo JSON_ERROR_STATE_MISMATCH . ' JSON_ERROR_STATE_MISMATCH' . '<br />';
echo JSON_ERROR_CTRL_CHAR . ' JSON_ERROR_CTRL_CHAR' . '<br />';
echo JSON_ERROR_SYNTAX . ' JSON_ERROR_SYNTAX' . '<br />';
echo JSON_ERROR_UTF8 . ' JSON_ERROR_UTF8' . '<br />';
echo JSON_ERROR_RECURSION . ' JSON_ERROR_RECURSION' . '<br />';
echo JSON_ERROR_INF_OR_NAN . ' JSON_ERROR_INF_OR_NAN' . '<br />';
echo JSON_ERROR_UNSUPPORTED_TYPE . ' JSON_ERROR_UNSUPPORTED_TYPE' . '<br />';/*
The above outputs :
0 JSON_ERROR_NONE
1 JSON_ERROR_DEPTH
2 JSON_ERROR_STATE_MISMATCH
3 JSON_ERROR_CTRL_CHAR
4 JSON_ERROR_SYNTAX
5 JSON_ERROR_UTF8
6 JSON_ERROR_RECURSION
7 JSON_ERROR_INF_OR_NAN
8 JSON_ERROR_UNSUPPORTED_TYPE
*/?>
wedge at atlanteans dot net ¶
4 years ago
here is a small updated version of utf8ize that has the following addition :
* It uses iconv instead of utf8_encode for potentially better result.
* It adds the support of objects variable
* It also update array key value (in a case I met I had to utf8ize the key as well as those were generated from a user input value)
Here is the code.
<?php
function utf8ize($d) {
if (is_array($d)) {
foreach ($d as $k => $v) {
unset($d[$k]);
$d[utf8ize($k)] = utf8ize($v);
}
} else if (is_object($d)) {
$objVars = get_object_vars($d);
foreach($objVars as $key => $value) {
$d->$key = utf8ize($value);
}
} else if (is_string ($d)) {
return iconv('UTF-8', 'UTF-8//IGNORE', utf8_encode($d));
}
return $d;
}
?>
williamprogphp at yahoo dot com dot br ¶
9 years ago
This is a quite simple and functional trick to validate JSON's strings.
<?phpfunction json_validate($string) {
if (is_string($string)) {
@json_decode($string);
return (json_last_error() === JSON_ERROR_NONE);
}
return false;
}
echo (json_validate('{"test": "valid JSON"}') ? "It's a JSON" : "NOT is a JSON"); // prints 'It's a JSON'
echo (json_validate('{test: valid JSON}') ? "It's a JSON" : "NOT is a JSON"); // prints 'NOT is a JSON' due to missing quotes
echo (json_validate(array()) ? "It's a JSON" : "NOT is a JSON"); // prints 'NOT is a JSON' due to a non-string argument
?>
Cheers
Открытые статические члены |
|
| static | encode ($data, $options=null) |
| static | decode ($data) |
Защищенные статические члены |
|
| static | serializeJson (&$data) |
| static | convertData ($data) |
| static | unConvertData ($data) |
| static | checkException ($options=0) |
| static | throwException ($e) |
См. определение в файле json.php строка 10
◆ checkException()
|
staticprotected |
Checks global error flag and raises exception if needed.
- Аргументы
-
integer $options Bitmasked options. When JSON_PARTIAL_OUTPUT_ON_ERROR passed no exception is raised.
- Возвращает
- void
- Исключения
См. определение в файле json.php строка 129
130 {
131 $e = json_last_error();
132
133 if ($e == JSON_ERROR_NONE)
134 {
135 return;
136 }
137
138 if ($e == JSON_ERROR_UTF8 && ($options & JSON_PARTIAL_OUTPUT_ON_ERROR))
139 {
140 return;
141 }
142
143 $message = sprintf(‘%s [%d]’, json_last_error_msg(), $e);
145 }
static throwException($e)
◆ convertData()
|
staticprotected |
Converts $data to UTF-8 charset.
- Аргументы
- Возвращает
- mixed
См. определение в файле json.php строка 101
102 {
104
105 return Encoding::convertEncoding($data, $culture->getCharset(), ‘UTF-8’);
106 }
◆ decode()
|
static |
Takes a JSON encoded string and converts it into a PHP variable.
- Аргументы
-
string $data The json string being decoded.
- Возвращает
- mixed
- Исключения
- См. также
- json_decode
См. определение в файле json.php строка 53
54 {
55 $res = json_decode($data, true);
56
58
59
60 if($res === null && strtolower($data) != ‘null’)
61 {
63 }
64
66 {
68 }
69
70 return $res;
71 }
static checkException($options=0)
static unConvertData($data)
◆ encode()
|
static |
Returns a string containing the JSON representation of $data.
- Аргументы
-
mixed $data The value being encoded. null $options Bitmasked options. Default is JSON_HEX_TAG|JSON_HEX_AMP|JSON_HEX_APOS|JSON_HEX_QUOT.
- Возвращает
- mixed
- Исключения
- См. также
- json_encode
Переопределяется в YandexJson.
См. определение в файле json.php строка 24
25 {
27 {
30 }
31
32 if (is_null($options))
33 {
34 $options = JSON_HEX_TAG|JSON_HEX_AMP|JSON_HEX_APOS|JSON_HEX_QUOT;
35 }
36
37 $res = json_encode($data, $options);
38
40
41 return $res;
42 }
static serializeJson(&$data)
static convertData($data)
◆ serializeJson()
|
staticprotected |
Executes serializeJson on JsonSerializable objects for non-UTF8 instances. We have to do it manually to prevent «malformed UTF-8 characters» error.
- Аргументы
См. определение в файле json.php строка 79
80 {
81 if($data instanceof JsonSerializable)
82 {
83 $data = $data->jsonSerialize();
84 }
85
86 if (is_iterable($data))
87 {
88 foreach ($data as $key => $value)
89 {
91 }
92 }
93 }
◆ throwException()
|
staticprotected |
Throws exception with message given.
- Аргументы
-
string $e Exception message.
- Возвращает
- void
- Исключения
См. определение в файле json.php строка 155
156 {
157 throw new ArgumentException(‘JSON error: ‘.$e, ‘data’);
158 }
◆ unConvertData()
|
staticprotected |
Converts $data from UTF-8 charset.
- Аргументы
- Возвращает
- mixed
См. определение в файле json.php строка 114
115 {
117
118 return Encoding::convertEncoding($data, ‘UTF-8’, $culture->getCharset());
119 }
◆ JSON_ERROR_UNKNOWN
const JSON_ERROR_UNKNOWN = -1
См. определение в файле json.php строка 12
Объявления и описания членов класса находятся в файле:
- C:/Bitrix/modules/main/lib/web/json.php