From Wikipedia, the free encyclopedia
This is a list of Hypertext Transfer Protocol (HTTP) response status codes. Status codes are issued by a server in response to a client’s request made to the server. It includes codes from IETF Request for Comments (RFCs), other specifications, and some additional codes used in some common applications of the HTTP. The first digit of the status code specifies one of five standard classes of responses. The optional message phrases shown are typical, but any human-readable alternative may be provided, or none at all.
Unless otherwise stated, the status code is part of the HTTP standard (RFC 9110).
The Internet Assigned Numbers Authority (IANA) maintains the official registry of HTTP status codes.[1]
All HTTP response status codes are separated into five classes or categories. The first digit of the status code defines the class of response, while the last two digits do not have any classifying or categorization role. There are five classes defined by the standard:
- 1xx informational response – the request was received, continuing process
- 2xx successful – the request was successfully received, understood, and accepted
- 3xx redirection – further action needs to be taken in order to complete the request
- 4xx client error – the request contains bad syntax or cannot be fulfilled
- 5xx server error – the server failed to fulfil an apparently valid request
1xx informational response
An informational response indicates that the request was received and understood. It is issued on a provisional basis while request processing continues. It alerts the client to wait for a final response. The message consists only of the status line and optional header fields, and is terminated by an empty line. As the HTTP/1.0 standard did not define any 1xx status codes, servers must not[note 1] send a 1xx response to an HTTP/1.0 compliant client except under experimental conditions.
- 100 Continue
- The server has received the request headers and the client should proceed to send the request body (in the case of a request for which a body needs to be sent; for example, a POST request). Sending a large request body to a server after a request has been rejected for inappropriate headers would be inefficient. To have a server check the request’s headers, a client must send
Expect: 100-continue
as a header in its initial request and receive a100 Continue
status code in response before sending the body. If the client receives an error code such as 403 (Forbidden) or 405 (Method Not Allowed) then it should not send the request’s body. The response417 Expectation Failed
indicates that the request should be repeated without theExpect
header as it indicates that the server does not support expectations (this is the case, for example, of HTTP/1.0 servers).[2] - 101 Switching Protocols
- The requester has asked the server to switch protocols and the server has agreed to do so.
- 102 Processing (WebDAV; RFC 2518)
- A WebDAV request may contain many sub-requests involving file operations, requiring a long time to complete the request. This code indicates that the server has received and is processing the request, but no response is available yet.[3] This prevents the client from timing out and assuming the request was lost.
- 103 Early Hints (RFC 8297)
- Used to return some response headers before final HTTP message.[4]
2xx success
This class of status codes indicates the action requested by the client was received, understood, and accepted.[1]
- 200 OK
- Standard response for successful HTTP requests. The actual response will depend on the request method used. In a GET request, the response will contain an entity corresponding to the requested resource. In a POST request, the response will contain an entity describing or containing the result of the action.
- 201 Created
- The request has been fulfilled, resulting in the creation of a new resource.[5]
- 202 Accepted
- The request has been accepted for processing, but the processing has not been completed. The request might or might not be eventually acted upon, and may be disallowed when processing occurs.
- 203 Non-Authoritative Information (since HTTP/1.1)
- The server is a transforming proxy (e.g. a Web accelerator) that received a 200 OK from its origin, but is returning a modified version of the origin’s response.[6][7]
- 204 No Content
- The server successfully processed the request, and is not returning any content.
- 205 Reset Content
- The server successfully processed the request, asks that the requester reset its document view, and is not returning any content.
- 206 Partial Content
- The server is delivering only part of the resource (byte serving) due to a range header sent by the client. The range header is used by HTTP clients to enable resuming of interrupted downloads, or split a download into multiple simultaneous streams.
- 207 Multi-Status (WebDAV; RFC 4918)
- The message body that follows is by default an XML message and can contain a number of separate response codes, depending on how many sub-requests were made.[8]
- 208 Already Reported (WebDAV; RFC 5842)
- The members of a DAV binding have already been enumerated in a preceding part of the (multistatus) response, and are not being included again.
- 226 IM Used (RFC 3229)
- The server has fulfilled a request for the resource, and the response is a representation of the result of one or more instance-manipulations applied to the current instance.[9]
3xx redirection
This class of status code indicates the client must take additional action to complete the request. Many of these status codes are used in URL redirection.[1]
A user agent may carry out the additional action with no user interaction only if the method used in the second request is GET or HEAD. A user agent may automatically redirect a request. A user agent should detect and intervene to prevent cyclical redirects.[10]
- 300 Multiple Choices
- Indicates multiple options for the resource from which the client may choose (via agent-driven content negotiation). For example, this code could be used to present multiple video format options, to list files with different filename extensions, or to suggest word-sense disambiguation.
- 301 Moved Permanently
- This and all future requests should be directed to the given URI.
- 302 Found (Previously «Moved temporarily»)
- Tells the client to look at (browse to) another URL. The HTTP/1.0 specification (RFC 1945) required the client to perform a temporary redirect with the same method (the original describing phrase was «Moved Temporarily»),[11] but popular browsers implemented 302 redirects by changing the method to GET. Therefore, HTTP/1.1 added status codes 303 and 307 to distinguish between the two behaviours.[10]
- 303 See Other (since HTTP/1.1)
- The response to the request can be found under another URI using the GET method. When received in response to a POST (or PUT/DELETE), the client should presume that the server has received the data and should issue a new GET request to the given URI.
- 304 Not Modified
- Indicates that the resource has not been modified since the version specified by the request headers If-Modified-Since or If-None-Match. In such case, there is no need to retransmit the resource since the client still has a previously-downloaded copy.
- 305 Use Proxy (since HTTP/1.1)
- The requested resource is available only through a proxy, the address for which is provided in the response. For security reasons, many HTTP clients (such as Mozilla Firefox and Internet Explorer) do not obey this status code.
- 306 Switch Proxy
- No longer used. Originally meant «Subsequent requests should use the specified proxy.»
- 307 Temporary Redirect (since HTTP/1.1)
- In this case, the request should be repeated with another URI; however, future requests should still use the original URI. In contrast to how 302 was historically implemented, the request method is not allowed to be changed when reissuing the original request. For example, a POST request should be repeated using another POST request.
- 308 Permanent Redirect
- This and all future requests should be directed to the given URI. 308 parallel the behaviour of 301, but does not allow the HTTP method to change. So, for example, submitting a form to a permanently redirected resource may continue smoothly.
4xx client errors
This class of status code is intended for situations in which the error seems to have been caused by the client. Except when responding to a HEAD request, the server should include an entity containing an explanation of the error situation, and whether it is a temporary or permanent condition. These status codes are applicable to any request method. User agents should display any included entity to the user.
- 400 Bad Request
- The server cannot or will not process the request due to an apparent client error (e.g., malformed request syntax, size too large, invalid request message framing, or deceptive request routing).
- 401 Unauthorized
- Similar to 403 Forbidden, but specifically for use when authentication is required and has failed or has not yet been provided. The response must include a WWW-Authenticate header field containing a challenge applicable to the requested resource. See Basic access authentication and Digest access authentication. 401 semantically means «unauthorised», the user does not have valid authentication credentials for the target resource.
- Some sites incorrectly issue HTTP 401 when an IP address is banned from the website (usually the website domain) and that specific address is refused permission to access a website.[citation needed]
- 402 Payment Required
- Reserved for future use. The original intention was that this code might be used as part of some form of digital cash or micropayment scheme, as proposed, for example, by GNU Taler,[13] but that has not yet happened, and this code is not widely used. Google Developers API uses this status if a particular developer has exceeded the daily limit on requests.[14] Sipgate uses this code if an account does not have sufficient funds to start a call.[15] Shopify uses this code when the store has not paid their fees and is temporarily disabled.[16] Stripe uses this code for failed payments where parameters were correct, for example blocked fraudulent payments.[17]
- 403 Forbidden
- The request contained valid data and was understood by the server, but the server is refusing action. This may be due to the user not having the necessary permissions for a resource or needing an account of some sort, or attempting a prohibited action (e.g. creating a duplicate record where only one is allowed). This code is also typically used if the request provided authentication by answering the WWW-Authenticate header field challenge, but the server did not accept that authentication. The request should not be repeated.
- 404 Not Found
- The requested resource could not be found but may be available in the future. Subsequent requests by the client are permissible.
- 405 Method Not Allowed
- A request method is not supported for the requested resource; for example, a GET request on a form that requires data to be presented via POST, or a PUT request on a read-only resource.
- 406 Not Acceptable
- The requested resource is capable of generating only content not acceptable according to the Accept headers sent in the request. See Content negotiation.
- 407 Proxy Authentication Required
- The client must first authenticate itself with the proxy.
- 408 Request Timeout
- The server timed out waiting for the request. According to HTTP specifications: «The client did not produce a request within the time that the server was prepared to wait. The client MAY repeat the request without modifications at any later time.»
- 409 Conflict
- Indicates that the request could not be processed because of conflict in the current state of the resource, such as an edit conflict between multiple simultaneous updates.
- 410 Gone
- Indicates that the resource requested was previously in use but is no longer available and will not be available again. This should be used when a resource has been intentionally removed and the resource should be purged. Upon receiving a 410 status code, the client should not request the resource in the future. Clients such as search engines should remove the resource from their indices. Most use cases do not require clients and search engines to purge the resource, and a «404 Not Found» may be used instead.
- 411 Length Required
- The request did not specify the length of its content, which is required by the requested resource.
- 412 Precondition Failed
- The server does not meet one of the preconditions that the requester put on the request header fields.
- 413 Payload Too Large
- The request is larger than the server is willing or able to process. Previously called «Request Entity Too Large» in RFC 2616.[18]
- 414 URI Too Long
- The URI provided was too long for the server to process. Often the result of too much data being encoded as a query-string of a GET request, in which case it should be converted to a POST request. Called «Request-URI Too Long» previously in RFC 2616.[19]
- 415 Unsupported Media Type
- The request entity has a media type which the server or resource does not support. For example, the client uploads an image as image/svg+xml, but the server requires that images use a different format.
- 416 Range Not Satisfiable
- The client has asked for a portion of the file (byte serving), but the server cannot supply that portion. For example, if the client asked for a part of the file that lies beyond the end of the file. Called «Requested Range Not Satisfiable» previously RFC 2616.[20]
- 417 Expectation Failed
- The server cannot meet the requirements of the Expect request-header field.[21]
- 418 I’m a teapot (RFC 2324, RFC 7168)
- This code was defined in 1998 as one of the traditional IETF April Fools’ jokes, in RFC 2324, Hyper Text Coffee Pot Control Protocol, and is not expected to be implemented by actual HTTP servers. The RFC specifies this code should be returned by teapots requested to brew coffee.[22] This HTTP status is used as an Easter egg in some websites, such as Google.com’s «I’m a teapot» easter egg.[23][24][25] Sometimes, this status code is also used as a response to a blocked request, instead of the more appropriate 403 Forbidden.[26][27]
- 421 Misdirected Request
- The request was directed at a server that is not able to produce a response (for example because of connection reuse).
- 422 Unprocessable Entity
- The request was well-formed but was unable to be followed due to semantic errors.[8]
- 423 Locked (WebDAV; RFC 4918)
- The resource that is being accessed is locked.[8]
- 424 Failed Dependency (WebDAV; RFC 4918)
- The request failed because it depended on another request and that request failed (e.g., a PROPPATCH).[8]
- 425 Too Early (RFC 8470)
- Indicates that the server is unwilling to risk processing a request that might be replayed.
- 426 Upgrade Required
- The client should switch to a different protocol such as TLS/1.3, given in the Upgrade header field.
- 428 Precondition Required (RFC 6585)
- The origin server requires the request to be conditional. Intended to prevent the ‘lost update’ problem, where a client GETs a resource’s state, modifies it, and PUTs it back to the server, when meanwhile a third party has modified the state on the server, leading to a conflict.[28]
- 429 Too Many Requests (RFC 6585)
- The user has sent too many requests in a given amount of time. Intended for use with rate-limiting schemes.[28]
- 431 Request Header Fields Too Large (RFC 6585)
- The server is unwilling to process the request because either an individual header field, or all the header fields collectively, are too large.[28]
- 451 Unavailable For Legal Reasons (RFC 7725)
- A server operator has received a legal demand to deny access to a resource or to a set of resources that includes the requested resource.[29] The code 451 was chosen as a reference to the novel Fahrenheit 451 (see the Acknowledgements in the RFC).
5xx server errors
The server failed to fulfil a request.
Response status codes beginning with the digit «5» indicate cases in which the server is aware that it has encountered an error or is otherwise incapable of performing the request. Except when responding to a HEAD request, the server should include an entity containing an explanation of the error situation, and indicate whether it is a temporary or permanent condition. Likewise, user agents should display any included entity to the user. These response codes are applicable to any request method.
- 500 Internal Server Error
- A generic error message, given when an unexpected condition was encountered and no more specific message is suitable.
- 501 Not Implemented
- The server either does not recognize the request method, or it lacks the ability to fulfil the request. Usually this implies future availability (e.g., a new feature of a web-service API).
- 502 Bad Gateway
- The server was acting as a gateway or proxy and received an invalid response from the upstream server.
- 503 Service Unavailable
- The server cannot handle the request (because it is overloaded or down for maintenance). Generally, this is a temporary state.[30]
- 504 Gateway Timeout
- The server was acting as a gateway or proxy and did not receive a timely response from the upstream server.
- 505 HTTP Version Not Supported
- The server does not support the HTTP version used in the request.
- 506 Variant Also Negotiates (RFC 2295)
- Transparent content negotiation for the request results in a circular reference.[31]
- 507 Insufficient Storage (WebDAV; RFC 4918)
- The server is unable to store the representation needed to complete the request.[8]
- 508 Loop Detected (WebDAV; RFC 5842)
- The server detected an infinite loop while processing the request (sent instead of 208 Already Reported).
- 510 Not Extended (RFC 2774)
- Further extensions to the request are required for the server to fulfill it.[32]
- 511 Network Authentication Required (RFC 6585)
- The client needs to authenticate to gain network access. Intended for use by intercepting proxies used to control access to the network (e.g., «captive portals» used to require agreement to Terms of Service before granting full Internet access via a Wi-Fi hotspot).[28]
Unofficial codes
The following codes are not specified by any standard.
- 419 Page Expired (Laravel Framework)
- Used by the Laravel Framework when a CSRF Token is missing or expired.
- 420 Method Failure (Spring Framework)
- A deprecated response used by the Spring Framework when a method has failed.[33]
- 420 Enhance Your Calm (Twitter)
- Returned by version 1 of the Twitter Search and Trends API when the client is being rate limited; versions 1.1 and later use the 429 Too Many Requests response code instead.[34] The phrase «Enhance your calm» comes from the 1993 movie Demolition Man, and its association with this number is likely a reference to cannabis.[citation needed]
- 430 Request Header Fields Too Large (Shopify)
- Used by Shopify, instead of the 429 Too Many Requests response code, when too many URLs are requested within a certain time frame.[35]
- 450 Blocked by Windows Parental Controls (Microsoft)
- The Microsoft extension code indicated when Windows Parental Controls are turned on and are blocking access to the requested webpage.[36]
- 498 Invalid Token (Esri)
- Returned by ArcGIS for Server. Code 498 indicates an expired or otherwise invalid token.[37]
- 499 Token Required (Esri)
- Returned by ArcGIS for Server. Code 499 indicates that a token is required but was not submitted.[37]
- 509 Bandwidth Limit Exceeded (Apache Web Server/cPanel)
- The server has exceeded the bandwidth specified by the server administrator; this is often used by shared hosting providers to limit the bandwidth of customers.[38]
- 529 Site is overloaded
- Used by Qualys in the SSLLabs server testing API to signal that the site can’t process the request.[39]
- 530 Site is frozen
- Used by the Pantheon Systems web platform to indicate a site that has been frozen due to inactivity.[40]
- 598 (Informal convention) Network read timeout error
- Used by some HTTP proxies to signal a network read timeout behind the proxy to a client in front of the proxy.[41]
- 599 Network Connect Timeout Error
- An error used by some HTTP proxies to signal a network connect timeout behind the proxy to a client in front of the proxy.
Internet Information Services
Microsoft’s Internet Information Services (IIS) web server expands the 4xx error space to signal errors with the client’s request.
- 440 Login Time-out
- The client’s session has expired and must log in again.[42]
- 449 Retry With
- The server cannot honour the request because the user has not provided the required information.[43]
- 451 Redirect
- Used in Exchange ActiveSync when either a more efficient server is available or the server cannot access the users’ mailbox.[44] The client is expected to re-run the HTTP AutoDiscover operation to find a more appropriate server.[45]
IIS sometimes uses additional decimal sub-codes for more specific information,[46] however these sub-codes only appear in the response payload and in documentation, not in the place of an actual HTTP status code.
nginx
The nginx web server software expands the 4xx error space to signal issues with the client’s request.[47][48]
- 444 No Response
- Used internally[49] to instruct the server to return no information to the client and close the connection immediately.
- 494 Request header too large
- Client sent too large request or too long header line.
- 495 SSL Certificate Error
- An expansion of the 400 Bad Request response code, used when the client has provided an invalid client certificate.
- 496 SSL Certificate Required
- An expansion of the 400 Bad Request response code, used when a client certificate is required but not provided.
- 497 HTTP Request Sent to HTTPS Port
- An expansion of the 400 Bad Request response code, used when the client has made a HTTP request to a port listening for HTTPS requests.
- 499 Client Closed Request
- Used when the client has closed the request before the server could send a response.
Cloudflare
Cloudflare’s reverse proxy service expands the 5xx series of errors space to signal issues with the origin server.[50]
- 520 Web Server Returned an Unknown Error
- The origin server returned an empty, unknown, or unexpected response to Cloudflare.[51]
- 521 Web Server Is Down
- The origin server refused connections from Cloudflare. Security solutions at the origin may be blocking legitimate connections from certain Cloudflare IP addresses.
- 522 Connection Timed Out
- Cloudflare timed out contacting the origin server.
- 523 Origin Is Unreachable
- Cloudflare could not reach the origin server; for example, if the DNS records for the origin server are incorrect or missing.
- 524 A Timeout Occurred
- Cloudflare was able to complete a TCP connection to the origin server, but did not receive a timely HTTP response.
- 525 SSL Handshake Failed
- Cloudflare could not negotiate a SSL/TLS handshake with the origin server.
- 526 Invalid SSL Certificate
- Cloudflare could not validate the SSL certificate on the origin web server. Also used by Cloud Foundry’s gorouter.
- 527 Railgun Error
- Error 527 indicates an interrupted connection between Cloudflare and the origin server’s Railgun server.[52]
- 530
- Error 530 is returned along with a 1xxx error.[53]
AWS Elastic Load Balancer
Amazon’s Elastic Load Balancing adds a few custom return codes
- 460
- Client closed the connection with the load balancer before the idle timeout period elapsed. Typically when client timeout is sooner than the Elastic Load Balancer’s timeout.[54]
- 463
- The load balancer received an X-Forwarded-For request header with more than 30 IP addresses.[54]
- 561 Unauthorized
- An error around authentication returned by a server registered with a load balancer. You configured a listener rule to authenticate users, but the identity provider (IdP) returned an error code when authenticating the user.[55]
Caching warning codes (obsoleted)
The following caching related warning codes were specified under RFC 7234. Unlike the other status codes above, these were not sent as the response status in the HTTP protocol, but as part of the «Warning» HTTP header.[56][57]
Since this «Warning» header is often neither sent by servers nor acknowledged by clients, this header and its codes were obsoleted by the HTTP Working Group in 2022 with RFC 9111.[58]
- 110 Response is Stale
- The response provided by a cache is stale (the content’s age exceeds a maximum age set by a Cache-Control header or heuristically chosen lifetime).
- 111 Revalidation Failed
- The cache was unable to validate the response, due to an inability to reach the origin server.
- 112 Disconnected Operation
- The cache is intentionally disconnected from the rest of the network.
- 113 Heuristic Expiration
- The cache heuristically chose a freshness lifetime greater than 24 hours and the response’s age is greater than 24 hours.
- 199 Miscellaneous Warning
- Arbitrary, non-specific warning. The warning text may be logged or presented to the user.
- 214 Transformation Applied
- Added by a proxy if it applies any transformation to the representation, such as changing the content encoding, media type or the like.
- 299 Miscellaneous Persistent Warning
- Same as 199, but indicating a persistent warning.
See also
- Custom error pages
- List of FTP server return codes
- List of HTTP header fields
- List of SMTP server return codes
- Common Log Format
Explanatory notes
- ^ Emphasised words and phrases such as must and should represent interpretation guidelines as given by RFC 2119
References
- ^ a b c «Hypertext Transfer Protocol (HTTP) Status Code Registry». Iana.org. Archived from the original on December 11, 2011. Retrieved January 8, 2015.
- ^ «RFC 9110: HTTP Semantics and Content, Section 10.1.1 «Expect»«.
- ^ Goland, Yaronn; Whitehead, Jim; Faizi, Asad; Carter, Steve R.; Jensen, Del (February 1999). HTTP Extensions for Distributed Authoring – WEBDAV. IETF. doi:10.17487/RFC2518. RFC 2518. Retrieved October 24, 2009.
- ^ Oku, Kazuho (December 2017). An HTTP Status Code for Indicating Hints. IETF. doi:10.17487/RFC8297. RFC 8297. Retrieved December 20, 2017.
- ^ Stewart, Mark; djna. «Create request with POST, which response codes 200 or 201 and content». Stack Overflow. Archived from the original on October 11, 2016. Retrieved October 16, 2015.
- ^ «RFC 9110: HTTP Semantics and Content, Section 15.3.4».
- ^ «RFC 9110: HTTP Semantics and Content, Section 7.7».
- ^ a b c d e Dusseault, Lisa, ed. (June 2007). HTTP Extensions for Web Distributed Authoring and Versioning (WebDAV). IETF. doi:10.17487/RFC4918. RFC 4918. Retrieved October 24, 2009.
- ^ Delta encoding in HTTP. IETF. January 2002. doi:10.17487/RFC3229. RFC 3229. Retrieved February 25, 2011.
- ^ a b «RFC 9110: HTTP Semantics and Content, Section 15.4 «Redirection 3xx»«.
- ^ Berners-Lee, Tim; Fielding, Roy T.; Nielsen, Henrik Frystyk (May 1996). Hypertext Transfer Protocol – HTTP/1.0. IETF. doi:10.17487/RFC1945. RFC 1945. Retrieved October 24, 2009.
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- ^ «Stripe API Reference – Errors». stripe.com. Retrieved October 28, 2019.
- ^ «RFC2616 on status 413». Tools.ietf.org. Archived from the original on March 7, 2011. Retrieved November 11, 2015.
- ^ «RFC2616 on status 414». Tools.ietf.org. Archived from the original on March 7, 2011. Retrieved November 11, 2015.
- ^ «RFC2616 on status 416». Tools.ietf.org. Archived from the original on March 7, 2011. Retrieved November 11, 2015.
- ^ TheDeadLike. «HTTP/1.1 Status Codes 400 and 417, cannot choose which». serverFault. Archived from the original on October 10, 2015. Retrieved October 16, 2015.
- ^ Larry Masinter (April 1, 1998). Hyper Text Coffee Pot Control Protocol (HTCPCP/1.0). doi:10.17487/RFC2324. RFC 2324.
Any attempt to brew coffee with a teapot should result in the error code «418 I’m a teapot». The resulting entity body MAY be short and stout.
- ^ I’m a teapot
- ^ Barry Schwartz (August 26, 2014). «New Google Easter Egg For SEO Geeks: Server Status 418, I’m A Teapot». Search Engine Land. Archived from the original on November 15, 2015. Retrieved November 4, 2015.
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- ^ «I Went to a Russian Website and All I Got Was This Lousy Teapot». PCMag. Retrieved December 18, 2022.
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- ^ Nielsen, Henrik Frystyk; Leach, Paul; Lawrence, Scott (February 2000). An HTTP Extension Framework. IETF. doi:10.17487/RFC2774. RFC 2774. Retrieved October 24, 2009.
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- ^ «SSL Labs API v3 Documentation». github.com.
- ^ «Platform Considerations | Pantheon Docs». pantheon.io. Archived from the original on January 6, 2017. Retrieved January 5, 2017.
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- ^
«Error message when you try to log on to Exchange 2007 by using Outlook Web Access: «440 Login Time-out»«. Microsoft. 2010. Retrieved November 13, 2013. - ^ «2.2.6 449 Retry With Status Code». Microsoft. 2009. Archived from the original on October 5, 2009. Retrieved October 26, 2009.
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- ^ «The HTTP status codes in IIS 7.0». Microsoft. July 14, 2009. Archived from the original on April 9, 2009. Retrieved April 1, 2009.
- ^ «ngx_http_request.h». nginx 1.9.5 source code. nginx inc. Archived from the original on September 19, 2017. Retrieved January 9, 2016.
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- ^ «Error 520: web server returns an unknown error». Cloudflare. Retrieved November 1, 2019.
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- ^ «Error 530». Cloudflare. Retrieved November 1, 2019.
- ^ a b «Troubleshoot Your Application Load Balancers – Elastic Load Balancing». docs.aws.amazon.com. Retrieved August 27, 2019.
- ^ «Troubleshoot your Application Load Balancers — Elastic Load Balancing». docs.aws.amazon.com. Retrieved January 24, 2021.
- ^ «Hypertext Transfer Protocol (HTTP/1.1): Caching». datatracker.ietf.org. Retrieved September 25, 2021.
- ^ «Warning — HTTP | MDN». developer.mozilla.org. Retrieved August 15, 2021. Some text was copied from this source, which is available under a Creative Commons Attribution-ShareAlike 2.5 Generic (CC BY-SA 2.5) license.
- ^ «RFC 9111: HTTP Caching, Section 5.5 «Warning»«. June 2022.
External links
- «RFC 9110: HTTP Semantics and Content, Section 15 «Status Codes»«.
- Hypertext Transfer Protocol (HTTP) Status Code Registry
принят и клиент может продолжать присылать запросы либо проигнорировать
этот ответ, если запрос был завершён.
клиента, содержащий заголовок
Upgrade:
, и указывает, чтосервер переключился на протокол, который был указан в заголовке. Эта
возможность позволяет перейти на несовместимую версию протокола и обычно
не используется.
обрабатывает его, но обработка ещё не завершена.
загружены заранее, пока сервер будет подготавливать основной ответ.
RFC 8297 (Experimental).
OK
метода HTTP, который был запрошен:
-
GET: «ПОЛУЧИТЬ». Запрошенный ресурс был найден и передан в теле
ответа. - HEAD: «ЗАГОЛОВОК». Заголовки переданы в ответе.
-
POST: «ПОСЫЛКА». Ресурс, описывающий результат действия сервера на
запрос, передан в теле ответа. -
TRACE: «ОТСЛЕЖИВАТЬ». Тело ответа содержит тело запроса полученного
сервером.
Этот код обычно присылается в ответ на запрос PUT «ПОМЕСТИТЬ».
нет способа с помощью HTTP отправить асинхронный ответ позже, который
будет показывать итог обработки запроса. Это предназначено для случаев,
когда запрос обрабатывается другим процессом или сервером, либо для
пакетной обработки.
которая возвращена, была предоставлена не от исходного сервера, а из
какого-нибудь другого источника. Во всех остальных ситуациях более
предпочтителен код ответа 200 OK.
ответа, которые могут быть полезны, присылаются. Клиент может
использовать их для обновления кешированных заголовков полученных ранее
для этого ресурса.
чтобы сообщить клиенту, что необходимо сбросить отображение документа,
который прислал этот запрос.
присылает заголовок диапазона, чтобы выполнить загрузку отдельно, в
несколько потоков.
«Множественный выбор». Этот код ответа присылается, когда запрос имеет
более чем один из возможных ответов. И User-agent или пользователь
должен выбрать один из ответов. Не существует стандартизированного
способа выбора одного из полученных ответов.
«Перемещён на постоянной основе». Этот код ответа значит, что URI
запрашиваемого ресурса был изменён. Возможно, новый URI будет
предоставлен в ответе.
«Найдено». Этот код ответа значит, что запрошенный ресурс
временно изменён. Новые изменения в URI могут быть доступны в
будущем. Таким образом, этот URI, должен быть использован клиентом в
будущих запросах.
направлять клиента для получения запрашиваемого ресурса в другой URI с
запросом GET.
значит, что запрошенный ресурс не был изменён. Таким образом, клиент
может продолжать использовать кешированную версию ответа.
доступен через прокси. Этот код ответа в основном не поддерживается из
соображений безопасности.
запросы должны использовать указанный прокси.»
получил запрошенный ресурс на другой URL-адрес с тем же методом, который
использовал предыдущий запрос. Данный код имеет ту же семантику, что код
ответа
302 Found
, за исключением того, что агентпользователя не должен изменять используемый метод HTTP: если в первом
запросе использовался
POST
, то во втором запросе такжедолжен использоваться
POST
.
«Перенаправление на постоянной основе». Это означает, что ресурс
теперь постоянно находится в другом URI, указанном в заголовке
Location:
HTTP Response. Данный код ответа имеет ту же
семантику, что и код ответа 301 Moved Permanently
, за
исключением того, что агент пользователя не должен изменять
используемый метод HTTP: если POST
использовался в первом
запросе, POST
должен использоваться и во втором запросе.
Примечание: Это экспериментальный код ответа,
Спецификация которого в настоящее время находится в черновом виде.
из-за неверного синтаксиса.
аутентификация. Статус похож на статус 403, но,в этом случае,
аутентификация возможна.
использования. Первоначальная цель для создания этого кода была в
использовании его для цифровых платёжных систем(на данный момент не
используется).
отказывается дать надлежащий ответ.
ответа, наверно, самый известный из-за частоты его появления в вебе.
деактивирован и не может быть использован. Два обязательных метода,
GET
и HEAD
, никогда не должны бытьдеактивированы и не должны возвращать этот код ошибки.
Этот ответ отсылается, когда веб сервер после выполнения
server-driven content negotiation, не нашёл контента, отвечающего критериям, полученным из user agent.
прокси сервера.
означает, что сервер хотел бы отключить это неиспользуемое соединение.
Этот метод используется все чаще с тех пор, как некоторые браузеры,
вроде Chrome и IE9, стали использовать
HTTP механизмы предварительного соединения
для ускорения сёрфинга (смотрите баг 634278, будущей
реализации этого механизма в Firefox). Также учитывайте, что некоторые
серверы прерывают соединения не отправляя подобных сообщений.
Этот ответ отсылается, когда запрос конфликтует с текущим состоянием
сервера.
Этот ответ отсылается, когда запрашиваемый контент удалён с сервера.
Запрос отклонён, потому что сервер требует указание заголовка
Content-Length
, но он не указан.
выполнить
Размер запроса превышает лимит, объявленный сервером. Сервер может
закрыть соединение, вернув заголовок Retry-After
его обработать
запрос отклонён
Range
не может бытьвыполнен; возможно, он выходит за пределы переданного URI
Expect
, не может быть выполнено сервером.
не знает как обработать.
обработан. Единственные методы, которые сервера должны поддерживать (и,
соответственно, не должны возвращать этот код) —
GET
иHEAD
.
качестве шлюза для получения ответа, нужного для обработки запроса,
получил недействительный (недопустимый) ответ.
причинами являются отключение сервера или то, что он перегружен.
Обратите внимание, что вместе с этим ответом удобная для
пользователей(user-friendly) страница должна отправлять объяснение
проблемы. Этот ответ должен использоваться для временных условий и
Retry-After:
HTTP-заголовок должен, если возможно,содержать предполагаемое время до восстановления сервиса. Веб-мастер
также должен позаботиться о заголовках, связанных с кешем, которые
отправляются вместе с этим ответом, так как эти ответы, связанные с
временными условиями, обычно не должны кешироваться.
не может получить ответ вовремя.
поддерживается сервером.
What is a 5xx Server Error?
A server returns a 5xx server error when it can’t successfully complete a client’s request.
5xx
means any HTTP status code that starts with 5
, so among others, this covers the 500
, 502
, and 503
errors.
A server error (5xx) is often referred to as a “5xx server error.” These mean one and the same thing, and we’ll use them interchangeably throughout this article.
Why you should care about 5xx server errors
5xx
server errors present a big issue, because they directly harm your visitor’s experience. Imagine having an eCommerce store, and your visitors keep receiving these server errors. Do you think they’ll keep trying and eventually purchase something?
No, they’ll go next door and buy from the competition.
And what about search engines like Google? If they receive 5xx
server errors just occasionally, then you probably don’t have much to fear. But if the 5xx
server errors are persistent, then it’s likely you’ll see a steady decline in organic traffic.
In this article we’ll cover why 5xx
server errors are bad for SEO, what the most common 5xx
server errors are, how to find out if your site’s server returns them, what causes this, and how to fix them.
Receive alerts when 5xx server errors occur
Be alerted in case of trouble so you can fix these errors before they hurt your SEO performance!
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Why every server error (5xx) hurts your SEO performance
We already know that 5xx
server errors make for a very poor user experience. But they’re also bad news for your SEO performance.
Here’s why:
-
When search engine crawlers (“crawlers” from here on out) consistently receive
5xx
server errors while crawling your site, they’ll want to avoid adding to the performance issues your site already has, so they’ll dial back their crawl efforts.Essentially this means that they’re lowering your site’s crawl budget. This results in your content getting (re)indexed more slowly.
Don’t forget: if your content isn’t indexed, it doesn’t rank.
-
When crawlers keep receiving these
5xx
server errors for your URLs, why would they grant your troubled pages high search results?Any visitors they send your way will likely have a poor user experience. So, when the
5xx
server errors persist, Google will start “demoting” your URLs – assigning lower positions or even completely removing them from its search engine result pages (SERPs). -
When pages aren’t available to crawlers, they won’t be able to (re)index them and rank them. They won’t know what the content is about, and these pages won’t surface in Google’s search results.
The bottom line: you could have the best content in the world, and the strongest links to your site, but you’ll have a really hard time ranking if your site is consistently suffering from 5xx
server errors.
The most common 5xx server errors
The most common 5xx
server errors are:
- 500 – Internal Server Error: the server had issues processing the request; this could have any one of a thousand reasons, often related to technical issues such as bugs or software incompatibilities.
- 502 – Bad Gateway: the request cannot be fulfilled successfully, because an upstream service (a service you’re expecting a response from) did not respond correctly. The upstream service can be running on the same machine or another machine, and it typically consists of a CGI component such as PHP and an application component such as a WordPress CMS.
-
503 – Service Unavailable: the server is temporarily unavailable, and will be available again later. Often the
503
server error is used when performing maintenance or when the server is too busy. -
504 – Gateway Timeout: this status code is closely related to the
502
server error. In the 504 server error, the server – while operating as a gateway or proxy – didn’t receive a response from another server in time. As we mentioned above, keep in mind that your web server is just a gateway too. What if your back-end takes too long to respond to your web server? - 509 – Bandwidth Limit Exceeded: your website has exceeded the server’s assigned bandwidth limits and thus is no longer available to the public. This frequently happens on shared hosting environments when they experience a sudden influx of visitors and/or crawlers. While this server error is frequently used, it’s not specified in any RFCs (see for yourself (opens in a new tab)).
-
524 – A timeout occurred: the Cloudflare CDN invented this server error and shows it when the origin server – your site – doesn’t respond in time. If the CDN doesn’t get a response, they can’t provide visitors and crawlers with one either. This results in the following error screen, which you may be familiar with:
Cloudflare returning an error 524
How to find 5xx server errors
It’s clear 5xx
server errors are bad for business, but how do you find them? We’ll kick off with the easiest and fastest one, followed by two more: using reports in Google Search Console (GSC) and log file analysis.
24/7 cloud-based monitoring
If your website is vital to your business, you need to monitor it nonstop for issues such as these 5xx
server errors. You want to be alerted in case of trouble. That’s exactly what the ContentKing platform does. Just plug in your site, the monitoring starts, and you’ll be alerted through Slack and/or email when something goes down:
Receive alerts when your site experiences 5xx server errors
Let us be your site’s watchdog and alert you in case of trouble.
Find 5xx server errors in GSC’s Index Coverage report
Google Search Console’s Index Coverage report is very useful for quickly tracking down any server errors Google has received.
- Log on to Google Search Console (opens in a new tab).
- At the top left, choose the right property.
- Then on the left, click on
Coverage
underIndex
. - Look under the
Error
issue category to see what URLs Google encountered5xx
server errors for: - Click on
Server error (5xx)
to jump to the overview of affected URLs.
Find 5xx server errors in GSC’s Crawl Stats report
Google Search Console’s Crawl Stats report shows you statistics about Google’s crawling history on your website. It lists what file types are requested most, what purpose their crawl request had (refresh content, or discover new content), and – this is what we’re interested in most – what “crawl response” they received.
- Log on to Google Search Console (opens in a new tab).
- At the top left, choose the right property.
- Then scroll all the way down, and click on
⚙️ Settings
in the left sidebar: - On the Settings screen, click
Open report
: - Look under
Crawl requests breakdown
>By response
to findServer error (5XX)
: - Click on
Server error (5XX)
to jump to the overview of affected URLs. Interestingly, it’s very possible that this report will show different URLs than the Index Coverage report does.
Find 5xx server errors in your server log files
And last but not least, you can go straight to the source: a log of all the requests that were made and what the server’s response was – your server’s log files.
While it can be notoriously difficult to get your hands on server log files, they are very valuable, because they provide a full picture of all the 5xx
server errors your server has returned.
At the end of the day, the Index Coverage and Crawl Stats reports are a digest, and they are limited to the 5xx server errors Google received.
What causes 5xx server errors?
There are thousands of reasons why your server might return a 5xx
server error; 5xx
server errors vary widely within their class and – while there are RFC standards and the like – it’s up to developers’ discretion to choose which 5xx server error is most applicable when a certain error occurs.
Additionally, it’s important to understand these server errors can occur on different levels, such as:
- CDN (e.g. Cloudflare or Akamai)
- Web server (e.g. Apache or nginx)
- Programming language (e.g. PHP or .NET)
- Application (e.g. WordPress or Magento)
- Plugin (e.g. a page speed optimization or contact form plugin)
Below we’ll cover some common examples of what can cause 5xx
server errors, but this is by no means an exhaustive list.
Code bugs and updates gone wrong
The most common reason for 500 – Internal Server Error
to occur is because of code bugs. The client makes a request, and while the server is processing that request, a bug causes some issue, and the server can’t successfully meet the request as a result.
Another common reason for the 500 server error is when running updates has gone wrong. For instance, when a new version of your CMS comes out, and you upgrade it, but some of your plugins aren’t compatible.
So provide your developers with leads about where to start debugging. Explain in as much detail as possible what went wrong, and where it went wrong.
The back-end has died
Your server will probably respond with a 502 – Bad Gateway
or 504 – Gateway Timeout
error if its back-end (such as the CGI component that runs the PHP powering your website) has crashed. Your server relies on its back-end to serve a page – and when the back-end doesn’t respond, it can’t produce anything.
An underpowered or misconfigured hosting platform
When you’ve got an underpowered or misconfigured hosting platform, and your server can’t handle all of the requests anymore, it’s likely to return the 503 – Service Unavailable
response.
You could be a victim of your own success because your PR campaign has drawn a pile of visitors to your site. Or maybe crawlers have gone rogue, continuously hammering your site.
There’s no “one size fits all” solution to this issue. It’s best to discuss this with your developers and hosting provider. The right solution depends on your specific situation, and oftentimes includes a combination of sub-solutions. To name a few:
- Upgrade your hosting platform (beef up your server’s specifications).
- Enable caching.
- Start using a Content Delivery Network (CDN).
- Improve code performance.
And in the case of bad crawlers, you could implement a bot management solution (opens in a new tab) and adjust your robots.txt to throttle bad crawlers (crawl-delay
directive) or keep them out entirely (disallow
directive).
Note that a crawler situation may eventually lead to the 509 – Bandwidth Limit Exceeded
server error.
Tackle 5xx server errors head on
You’re bound to encounter 5xx
server errors at some point. What matters most is that you quickly find out about them, and that you deal with them swiftly. Don’t let 5xx
server errors hurt your SEO performance.
Monitor your website around the clock and leverage Google Search Console’s tools and your server log files to investigate and debug these issues. Keep an open mind as to the reason why you’re getting these 5xx
server errors. There are literally thousands of possible reasons out there, and they can happen on various levels in your architecture.
Let ContentKing do the heavy lifting for you
ContentKing will be your site’s watchdog 24/7 and alert you in case of trouble.
Read the full Academy article to learn everything about HTTP Status Codes
HyperText Transfer Protocol (HTTP) is a communication protocol used when browser sends the request to the server to get the response. During this process, server returns a code to indicate the status of the received request. This HTTP status code is very useful in troubleshooting the connection errors and fix the problems.
Here are the five different categories of status codes used in HTTP communication protocol:
- 1xx status codes for information
- 2xx status codes for success
- 3xx status codes for redirection
- 4xx status codes for client errors
- 5xx status codes for server errors
5xx HTTP Status Codes – Server Error
These are the HTTP status or error codes most frequently seen in the web browser window. 5xx error codes are returned by the web server when it encounters a problem during processing of the requested resource by the client.
500 – Internal Server Error
When the server encountered an unexpected condition which stops it from responding to the request then it returns an error code “500 – Internal Server Error“.
Generally, internal server error happens due to incorrect configuration. If you are a website owner, check the server’s configuration or get in touch with your web hosting company to fix the error.
501 – Method Not Supported
When the server does not able to provide the requested resource due to unsupported or unrecognized method used in the request then the code “501 – Not Implemented is received.
502 – Gateway Error
When a request prompts the server1 to act as a gateway or proxy to get a response from another server2 and if the server1 received an unacceptable response from the server2 then the code “502 – Bad Gateway” is received.
503 – Service Unavailable
When a request is received by the server at the time it is overloaded by other requests or it is under planned maintenance downtime then the code “503 – Service Unavailable” is received.
504 – Gateway Timeout
When the server1 is acting as an external gateway or proxy and did not receive the response on time from the next server2 further up in the request chain which it tried to access in order to fulfill the request then code “504 – Gateway Timeout” is received.
505 – HTTP Version is Not Supported
When the server does not support the HTTP protocol version used in the request message then the code “505 – HTTP Version Not Supported” is received.
507 – Insufficient Space
When the server runs out of hard disk space and no more accommodate the request then the code “507 – Insufficient Storage” is received.
510 – Extensions are Missing
When the server can’t process the request due to unsupported extension is requested then the code “510 – Not Extended” is received.
Умные люди придумали коды, по которым можно определить, что произошло с HTTP-запросом. Успешен ли он, произошло ли перенаправление. Или же все закончилось ошибкой. Как раз об ошибках и будем говорить в этой статье. Вкратце расскажу, какие они бывают и с чем связаны.
А еще тут будет парочка забавных (и не очень) пикч и анимаций на тему описанных ошибок. Хоть какое-то развлечение.
Ошибки со стороны клиента (4xx)
Для начала перечислим коды ошибок на стороне клиента. Вина за их появление ложится на плечи обоих участников соединения.
400 Bad Request
Такой ответ от браузера можно получить в том случае, если сервер не смог правильно отреагировать на запрос со стороны пользователя. Часто код 400 возникает при попытке клиента получить доступ к серверу без соблюдения правил оформления синтаксиса протокола передачи гипертекста (HTTP). Повторный запрос не стоит отправлять до тех пор, пока не будет исправлена ошибка (или несколько из них).
401 Unauthorized
Код 401 возникает при попытке клиента получить доступ к серверу, используя неправильные данные для авторизации. По сути, используется, когда пользователь вводит неправильный логин и пароль на ресурсе, где требуется эта информация для входа. Читайте: Как исправить ошибку 401
402 Payment Required
Эта ошибка сообщает клиенту о том, что для успешного выполнения запроса ему необходимо оплатить доступ к серверу. Изначально код 402 должен был стать неким стандартом для цифровой валюты и оплаты контента в сети. Но не срослось. До сих пор нет единого решения по поводу того, как должны выглядеть платежи в сети. Также нет и единого решения по поводу того, как стоит использовать 402.
Все еще считается, что код существует с расчетом на будущее. Сейчас почти не используется и поддерживается не всеми браузерами.
403 Forbidden
Почти то же, что и 401. Сервер снова не разрешает к нему подключиться, хотя с запросом все в порядке. Просто нет доступа. Причем повторная авторизация с другими логином и паролем никак не помогут. Все вопросы к владельцам сервера (но не всегда). Инструкция по устранению ошибки.
Творчество на тему знаменитой киносаги
404 Not Found
Легендарная ошибка, ставшая популярным мемом. 404 оповещает клиента о том, что его запрос ведет в никуда. Код возникает, когда пользователь пытается попасть на страницу, которой не существует. Например, когда случайно ошибается при вводе ссылки и вводит ее с опечаткой. Или же пытается получить доступ к странице, которой на сайте уже нет.
В отличие от других кодов, страницу с 404 частенько кастомизируют, создавая для нее уникальный дизайн. Мало того, что это выглядит симпатичнее, так еще и полезнее для посетителей. Можно прямо на странице с ошибкой разъяснить, что произошло и как дальше действовать.
И таких вариаций тысячи. Каждый пытается добавить в оформление что-то свое.
405 Method Not Allowed
405 сообщает клиенту о том, что метод, используемый при запросе, не разрешен. В качестве примера можно привести попытку со стороны клиента ввести данные в форму с помощью GET, когда она работает только с POST. Ну и в таком же духе.
406 Not Acceptable
Ошибка 406 сообщает о том, что страница передает контент, который не может быть распознан клиентом. Возможно, проблема в методе сжатия или в формате страницы. Иногда сюда же приплетают неправильные настройки кодировки.
Этот код редко используют на практике, так как его появления можно избежать, предоставив пользователю информацию на сайте в том виде, который его браузер способен принять. Посетитель сайта по итогу получит не то, что ожидал, но хотя бы не ошибку.
407 Proxy Authentication Required
Этот код тоже похож на 401. Только на этот раз логин и пароль нужны не для основного сервера, а для прокси, который находится между клиентом и сервером. Обычно в теле ошибки содержится информация о том, как можно правильно пройти авторизацию и получить доступ к ресурсу.
408 Request Timeout
408 говорит нам о том, что сервер пожелал разорвать соединение с клиентом, потому что оно никак не используется. Происходит это в том случае, если сервер буквально устал ждать, пока наладится соединение с ним. Поэтому такую ошибку часто можно лицезреть после очень долгой и безуспешной загрузки какого-нибудь сайта.
Многие серверы не отправляют никаких сообщений, а просто прерывают соединение по той же причине. На запрос уходит больше времени, чем на то полагается.
В Мистере Роботе частенько называли серии в честь ошибок HTTP (весь четвертый сезон в нумерации 4хх). В честь 408, например, назвали восьмую серию четвертого сезона
409 Conflict
Сообщение о конфликте возникает, когда запрос со стороны клиента не соответствует тому, чего ожидает сервер. В качестве примера приводят проблемы при проверки версий, когда пользователь пытается с помощью метода PUT загрузить на сервер новый файл, но там уже имеется более новая версия того же файла. Конфликта версий можно легко избежать, загрузив корректную версию.
410 Gone
Своего рода аналог 404. Разница лишь в том, что 410 намекает на перманентность отсутствия страницы. Так что этот код стоит использовать, когда на 100% уверен, что страница ушла в небытие (ну или с текущего адреса) навсегда. В любом другом случае есть универсальный 404.
411 Length Required
411 оповещает пользователя о том, что сервер не желает принимать запрос со стороны клиента, потому что в нем не определен заголовок Content-Length. Да, это первый код в подборке, который смогут понять только люди, сведущие в настройке серверов. По-простому уложить сущность HTML-заголовков в этот материал не получится.
412 Precondition Failed
Еще один код, сообщающий о том, что сервер отклонил запрос пользователя и не разрешает доступ к выбранному ресурсу. Проблемы возникают при неправильной настройке работы методов, отличающихся от GET и HEAD.
413 Payload Too Large/Request Entity Too Large
Код 413 говорит нам, что запрос, который посылает клиент на сервер, слишком большой. Поэтому сервер отказывается его обрабатывать и разрывает соединение. Обычно это происходит при попытке загрузить на ресурс какой-то файл, превышающий ограничение, выставленное в настройках сервера. Соответственно, решается проблема изменением настроек сервера.
414 URI Too Long
Чем-то этот код похож на предыдущий. Здесь тоже идет речь о превышение лимита. Только теперь это касается не запроса со стороны клиента, а длины URI. То есть ссылки. Выходит, что адрес, используемый клиентом, больше, чем тот, что может обработать сервер. Как-то так.
Такая ошибка иногда выскакивает при попытке взломать ресурс. Сайт так реагирует на слишком частые попытки воспользоваться потенциальными дырами в безопасности.
415 Unsupported Media Type
Ошибка 415 возникает, когда клиент пытается загрузить на сервер данные в неподходящем формате. В таком случае сервер просто отказывается принимать посылаемые файлы и разрывает соединение. Как и в случае с 413.
416 Range Not Satisfiable
Подобный ответ можно ожидать, если клиент запрашивает у сервера определенные данные, но эти данные на сервере не соответствуют запросу. То есть, грубо говоря, вы просите у сервера какой-то набор данных с заранее заданным размером, а в итоге оказывается, что размер этих данных меньше, чем объем, указанный в запросе. Серверу ничего не остается, кроме как послать вас, ведь он не обучен поведению в таких ситуациях.
417 Expectation Failed
Такая ошибка высвечивается, когда ожидания сервера не совпадают с данными в запросе клиента. Сведения об ожиданиях прописываются в заголовке Expect заранее. Так что можно ознакомиться с ними, чтобы выяснить, как решить названную проблему.
418 I’m a teapot
Код 418 можно увидеть, если сервер откажется варить кофе, потому что он чайник. Это первоапрельская шутка. Естественно, 418 не используется нигде всерьез и просто существует как дань памяти программистам-юмористам, придумавшим это в 1998 году.
У Google получился такой симпатичный чайник
421 Misdirected Request
Появляется когда запрос клиента переправляется на сервер, который не может дать на него адекватный ответ. Например, если запрос был отправлен на ресурс, который вообще не настроен обрабатывать запросы извне.
Чтобы исправить проблему, можно попробовать переподключиться к ресурсу заново или попробовать другое соединение.
422 Unprocessable Entity
Код 422 говорит, что сервер вроде бы принял запрос, понял его, все хорошо, но из-за семантических ошибок корректно обработать не смог. Значит, где-то в запросе затаилась логическая ошибка, мешающая корректному взаимодействию клиента и сервера. Надо ее найти и исправить.
423 Locked
Обычно на этот код напарываются, когда запрашиваемый ресурс оказывается под защитой. Используемые клиентом методы блокируются на уровне сервера. Это делается, чтобы обезопасить данные, хранящиеся на защищенной странице. Без логина и пароля выудить информацию с такого сервера не получится.
424 Failed Dependency
424 сообщает о том, что для выполнения запроса со стороны клиента успешно должна завершиться еще одна или несколько параллельных операций. Если какая-то из них «провалится», то «помрет» все соединение сразу, и обработать запрос до конца не получится. Аналогичное происходит, если некорректно был обработан один из предыдущих запросов.
425 Too Early
Появляется в ответ на запрос, который может быть моментально запущен заново. Сервер не рискует и не берется за его обработку, чтобы не подставиться под так называемую «атаку повторного воспроизведения».
426 Upgrade Required
Тут нам прямо сообщают, что сервер не желает с нами общаться, пока мы не перейдем на более современный протокол. Наткнуться на такую ошибку очень тяжело, но в случае появления, скорее всего, будет достаточно установить браузер посвежее.
428 Precondition Required
428 выскакивает, если пользователь отправляет запрос на сервер, но получает некорректные или неактуальные данные. Так ресурс оповещает о необходимости внести в запрос информацию о предварительных условиях обработки данных. Только так он сможет гарантировать получение клиентом нужной информации.
429 Too Many Requests
Здесь все просто. Ошибка появляется, когда клиент отправляет на сервер слишком много запросов в короткий промежуток времени. Очень похоже на поведение взломщиков. По этой причине запрос моментально блокируется.
431 Request Header Fields Too Large
Из названия понятно, что ошибка с кодом 431 появляется из-за того, что в запросе клиента используются слишком длинные заголовки (неважно, один или несколько из них). Исправляется это с помощью сокращения заголовков и повторной отправки запроса. В теле ошибки обычно отображается краткая информация о том, как пользователь может решить эту проблему самостоятельно.
444 No Response
Этот код вам вряд ли удастся увидеть. Он отображается в лог-файлах, чтобы подтвердить, что сервер никак не отреагировал на запрос пользователя и прервал соединение.
449 Retry With
Код используется в расширениях компании Microsoft. Он сигнализирует о том, что запрос от клиента не может быть принят сервером. Причиной становятся неверно указанные параметры. Сама 449 ошибка говорит о необходимости скорректировать запрос и повторить его снова, подготовив к работе с сервером.
450 Blocked by Windows Parental Controls
450 код увидят дети, попавшие под действие системы «Родительский контроль» компании Microsoft. По сути, ошибка говорит о том, что с компьютера попытались зайти на заблокированный ресурс. Избежать этой ошибки можно изменением параметров родительского контроля.
451 Unavailable For Legal Reasons
Этот код сообщает клиенту, что он не может попасть на запрашиваемый ресурс из юридических соображений. Скорее всего, доступ был заблокирован из-за каких-нибудь государственных санкций, нового законодательства или цензуры со стороны властей. В общем, все вопросы к государству и провайдеру связи.
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Список ошибок на стороне сервера (5xx)
Теперь поговорим об ошибках, которые возникают где-то на сервере. Все они связаны с запросами, которые не удается обработать на том конце. Пользователь зачастую в их появлении не виноват.
500 Internal Server Error
Этот код возникает, когда сервер сталкивается с непредвиденными обстоятельствами. Такими, которые и сам не может пояснить. Как, собственно, и завершить запрос со стороны пользователя. По факту, эта ошибка говорит нам что-то вроде «Я не могу подобрать более подходящий код ошибки, поэтому лови 500 и делай с этим, что хочешь». Мы писали о нем чуть подробнее тут.
Дело не в тебе, дело во мне (С)
501 Not Implemented
501 говорит нам, что функциональность, необходимая для обработки запроса со стороны клиента, попросту не реализована на сервере. Он не сможет корректно обработать используемый метод.
Иногда в теле ошибки еще пишут что-то в духе «Приходите попозже, возможно, в будущем нужная функция появится».
502 Bad Getaway
Можно встретить в том случае, если запрашиваемый сервер выступает в роли шлюза или прокси. Возникает из-за несогласования протоколов между вышестоящим серверов и его шлюзом. Рассказываем о том, как ее исправить, в этой статье.
503 Service Unavailable
Появляется, когда сервер не может обработать запрос клиента по одной из двух технических причин:
- Слишком много пользователей в текущий момент пытаются отправить запросы, и у сервера не остается ресурсов, чтобы ответить кому-либо еще.
- На сервере ведутся технические работы, временно блокирующие его работу.
Обычно ошибка 503 носит временный характер, и для ее решения достаточно немного подождать.
504 Gateway Timeout
Ошибка похожа на 408. Здесь же прокси-сервер пытается выйти на контакт с вышестоящим сервером, но не успевает это сделать до истечения тайм-аута. Отсюда и ошибка.
505 HTTP Version Not Supported
Этот код похож на 426. Он тоже связан с неподходящей версией протокола HTTP. В этом случае нужно обеспечить и клиента, и сервер единой версией. Она, как правило, указывается в запросе со стороны пользователя.
506 Variant Also Negotiates
Обычно с такой ошибкой сталкиваются только в том случае, если сервер изначально настроен неправильно. То есть это не сиюминутная проблема, а что-то серьезное на уровне базовой конфигурации. Тут придется потрудиться разработчикам. Выявить проблему и разрешить ее.
507 Insufficient Storage
Код 507 встречается в тех ситуациях, когда серверу не хватает пространства в хранилище для обработки запроса со стороны клиента. Проблема решается освобождением места или расширением доступного пространства. Тогда сервер сможет без проблем обработать запрос пользователя.
508 Loop Detected
Таким кодом сервер отзовется в случае, если заметит бесконечный цикл в запросе клиента. Можно расценивать его как провал запроса и выполняемой операции в целом.
509 Bandwidth Limit Exceeded
Возникает, если сервер начинает потреблять больше трафика, чем ему позволено.
510 Not Extended
Появляется, если клиент посылает запрос на использование какого-либо расширения, отсутствующего на сервере. Чтобы исправить проблему, надо убрать декларирование неподдерживаемого расширения из запроса или добавить поддержку на сервер.
511 Network Authentication Required
511 код говорит о том, что перед тем как выйти в сеть, надо авторизоваться (ввести логин и пароль). Можно воспринимать это неким PPPoE подключением, когда от клиента требуются данные для авторизации.
Заключение
Закончили. Это все ошибки, которыми отзывается HTTP, если на стороне сервера или клиента что-то пошло не так. Наткнуться на большую их часть довольно тяжело. Особенно, если вы раньше только серфили в интернете, а не занимались разработкой сайтов. А тем, кто входит в эту стезю, полезно знать основные ошибки, так как, скорее всего, придется не раз их исправлять.
REST APIs use the Status-Line part of an HTTP response message to inform clients of their request’s overarching result. RFC 2616 defines the Status-Line syntax as shown below:
Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
HTTP defines these standard status codes that can be used to convey the results of a client’s request. The status codes are divided into five categories.
- 1xx: Informational – Communicates transfer protocol-level information.
- 2xx: Success – Indicates that the client’s request was accepted successfully.
- 3xx: Redirection – Indicates that the client must take some additional action in order to complete their request.
- 4xx: Client Error – This category of error status codes points the finger at clients.
- 5xx: Server Error – The server takes responsibility for these error status codes.
1xx Status Codes [Informational]
Status Code |
Description |
---|---|
100 Continue |
An interim response. Indicates to the client that the initial part of the request has been received and has not yet been rejected by the server. The client SHOULD continue by sending the remainder of the request or, if the request has already been completed, ignore this response. The server MUST send a final response after the request has been completed. |
101 Switching Protocol |
Sent in response to an Upgrade request header from the client, and indicates the protocol the server is switching to. |
102 Processing (WebDAV) |
Indicates that the server has received and is processing the request, but no response is available yet. |
103 Early Hints |
Primarily intended to be used with the |
2xx Status Codes [Success]
Status Code |
Description |
---|---|
200 OK |
Indicates that the request has succeeded. |
201 Created |
Indicates that the request has succeeded and a new resource has been created as a result. |
202 Accepted |
Indicates that the request has been received but not completed yet. It is typically used in log running requests and batch processing. |
203 Non-Authoritative Information |
Indicates that the returned metainformation in the entity-header is not the definitive set as available from the origin server, but is gathered from a local or a third-party copy. The set presented MAY be a subset or superset of the original version. |
204 No Content |
The server has fulfilled the request but does not need to return a response body. The server may return the updated meta information. |
205 Reset Content |
Indicates the client to reset the document which sent this request. |
206 Partial Content |
It is used when the |
207 Multi-Status (WebDAV) |
An indicator to a client that multiple operations happened, and that the status for each operation can be found in the body of the response. |
208 Already Reported (WebDAV) |
Allows a client to tell the server that the same resource (with the same binding) was mentioned earlier. It never appears as a true HTTP response code in the status line, and only appears in bodies. |
226 IM Used |
The server has fulfilled a GET request for the resource, and the response is a representation of the result of one or more instance-manipulations applied to the current instance. |
3xx Status Codes [Redirection]
Status Code |
Description |
---|---|
300 Multiple Choices |
The request has more than one possible response. The user-agent or user should choose one of them. |
301 Moved Permanently |
The URL of the requested resource has been changed permanently. The new URL is given by the |
302 Found |
The URL of the requested resource has been changed temporarily. The new URL is given by the |
303 See Other |
The response can be found under a different URI and SHOULD be retrieved using a GET method on that resource. |
304 Not Modified |
Indicates the client that the response has not been modified, so the client can continue to use the same cached version of the response. |
305 Use Proxy (Deprecated) |
Indicates that a requested response must be accessed by a proxy. |
306 (Unused) |
It is a reserved status code and is not used anymore. |
307 Temporary Redirect |
Indicates the client to get the requested resource at another URI with same method that was used in the prior request. It is similar to |
308 Permanent Redirect (experimental) |
Indicates that the resource is now permanently located at another URI, specified by the |
4xx Status Codes (Client Error)
Status Code |
Description |
---|---|
400 Bad Request |
The request could not be understood by the server due to incorrect syntax. The client SHOULD NOT repeat the request without modifications. |
401 Unauthorized |
Indicates that the request requires user authentication information. The client MAY repeat the request with a suitable Authorization header field |
402 Payment Required (Experimental) |
Reserved for future use. It is aimed for using in the digital payment systems. |
403 Forbidden |
Unauthorized request. The client does not have access rights to the content. Unlike 401, the client’s identity is known to the server. |
404 Not Found |
The server can not find the requested resource. |
405 Method Not Allowed |
The request HTTP method is known by the server but has been disabled and cannot be used for that resource. |
406 Not Acceptable |
The server doesn’t find any content that conforms to the criteria given by the user agent in the |
407 Proxy Authentication Required |
Indicates that the client must first authenticate itself with the proxy. |
408 Request Timeout |
Indicates that the server did not receive a complete request from the client within the server’s allotted timeout period. |
409 Conflict |
The request could not be completed due to a conflict with the current state of the resource. |
410 Gone |
The requested resource is no longer available at the server. |
411 Length Required |
The server refuses to accept the request without a defined Content- Length. The client MAY repeat the request if it adds a valid |
412 Precondition Failed |
The client has indicated preconditions in its headers which the server does not meet. |
413 Request Entity Too Large |
Request entity is larger than limits defined by server. |
414 Request-URI Too Long |
The URI requested by the client is longer than the server can interpret. |
415 Unsupported Media Type |
The media-type in |
416 Requested Range Not Satisfiable |
The range specified by the |
417 Expectation Failed |
The expectation indicated by the |
418 I’m a teapot (RFC 2324) |
It was defined as April’s lool joke and is not expected to be implemented by actual HTTP servers. (RFC 2324) |
420 Enhance Your Calm (Twitter) |
Returned by the Twitter Search and Trends API when the client is being rate limited. |
422 Unprocessable Entity (WebDAV) |
The server understands the content type and syntax of the request entity, but still server is unable to process the request for some reason. |
423 Locked (WebDAV) |
The resource that is being accessed is locked. |
424 Failed Dependency (WebDAV) |
The request failed due to failure of a previous request. |
425 Too Early (WebDAV) |
Indicates that the server is unwilling to risk processing a request that might be replayed. |
426 Upgrade Required |
The server refuses to perform the request. The server will process the request after the client upgrades to a different protocol. |
428 Precondition Required |
The origin server requires the request to be conditional. |
429 Too Many Requests |
The user has sent too many requests in a given amount of time (“rate limiting”). |
431 Request Header Fields Too Large |
The server is unwilling to process the request because its header fields are too large. |
444 No Response (Nginx) |
The Nginx server returns no information to the client and closes the connection. |
449 Retry With (Microsoft) |
The request should be retried after performing the appropriate action. |
450 Blocked by Windows Parental Controls (Microsoft) |
Windows Parental Controls are turned on and are blocking access to the given webpage. |
451 Unavailable For Legal Reasons |
The user-agent requested a resource that cannot legally be provided. |
499 Client Closed Request (Nginx) |
The connection is closed by the client while HTTP server is processing its request, making the server unable to send the HTTP header back. |
5xx Status Codes (Server Error)
Status Code |
Description |
---|---|
500 Internal Server Error |
The server encountered an unexpected condition that prevented it from fulfilling the request. |
501 Not Implemented |
The HTTP method is not supported by the server and cannot be handled. |
502 Bad Gateway |
The server got an invalid response while working as a gateway to get the response needed to handle the request. |
503 Service Unavailable |
The server is not ready to handle the request. |
504 Gateway Timeout |
The server is acting as a gateway and cannot get a response in time for a request. |
505 HTTP Version Not Supported (Experimental) |
The HTTP version used in the request is not supported by the server. |
506 Variant Also Negotiates (Experimental) |
Indicates that the server has an internal configuration error: the chosen variant resource is configured to engage in transparent content negotiation itself, and is therefore not a proper endpoint in the negotiation process. |
507 Insufficient Storage (WebDAV) |
The method could not be performed on the resource because the server is unable to store the representation needed to successfully complete the request. |
508 Loop Detected (WebDAV) |
The server detected an infinite loop while processing the request. |
510 Not Extended |
Further extensions to the request are required for the server to fulfill it. |
511 Network Authentication Required |
Indicates that the client needs to authenticate to gain network access. |
6. REST Specific HTTP Status Codes
200 (OK)
It indicates that the REST API successfully carried out whatever action the client requested and that no more specific code in the 2xx series is appropriate.
Unlike the 204 status code, a 200 response should include a response body. The information returned with the response is dependent on the method used in the request, for example:
- GET an entity corresponding to the requested resource is sent in the response;
- HEAD the entity-header fields corresponding to the requested resource are sent in the response without any message-body;
- POST an entity describing or containing the result of the action;
- TRACE an entity containing the request message as received by the end server.
201 (Created)
A REST API responds with the 201 status code whenever a resource is created inside a collection. There may also be times when a new resource is created as a result of some controller action, in which case 201 would also be an appropriate response.
The newly created resource can be referenced by the URI(s) returned in the entity of the response, with the most specific URI for the resource given by a Location header field.
The origin server MUST create the resource before returning the 201 status code. If the action cannot be carried out immediately, the server SHOULD respond with a 202 (Accepted) response instead.
202 (Accepted)
A 202 response is typically used for actions that take a long while to process. It indicates that the request has been accepted for processing, but the processing has not been completed. The request might or might not be eventually acted upon, or even maybe disallowed when processing occurs.
Its purpose is to allow a server to accept a request for some other process (perhaps a batch-oriented process that is only run once per day) without requiring that the user agent’s connection to the server persist until the process is completed.
The entity returned with this response SHOULD include an indication of the request’s current status and either a pointer to a status monitor (job queue location) or some estimate of when the user can expect the request to be fulfilled.
204 (No Content)
The 204 status code is usually sent out in response to a PUT
, POST
, or DELETE
request when the REST API declines to send back any status message or representation in the response message’s body.
An API may also send 204 in conjunction with a GET request to indicate that the requested resource exists, but has no state representation to include in the body.
If the client is a user agent, it SHOULD NOT change its document view from that which caused the request to be sent. This response is primarily intended to allow input for actions to take place without causing a change to the user agent’s active document view. However, any new or updated metainformation SHOULD be applied to the document currently in the user agent’s dynamic view.
The 204 response MUST NOT include a message-body and thus is always terminated by the first empty line after the header fields.
301 (Moved Permanently)
The 301 status code indicates that the REST API’s resource model has been significantly redesigned, and a new permanent URI has been assigned to the client’s requested resource. The REST API should specify the new URI in the response’s Location header, and all future requests should be directed to the given URI.
You will hardly use this response code in your API as you can always use the API versioning for the new API while retaining the old one.
302 (Found)
The HTTP response status code 302 Found is a common way of performing URL redirection. An HTTP response with this status code will additionally provide a URL in the Location header field. The user agent (e.g., a web browser) is invited by a response with this code to make a second. Otherwise identical, request to the new URL specified in the location field.
Many web browsers implemented this code in a manner that violated this standard, changing the request type of the new request to GET, regardless of the type employed in the original request (e.g., POST). RFC 1945 and RFC 2068 specify that the client is not allowed to change the method on the redirected request. The status codes 303 and 307 have been added for servers that wish to make unambiguously clear which kind of reaction is expected of the client.
303 (See Other)
A 303 response indicates that a controller resource has finished its work, but instead of sending a potentially unwanted response body, it sends the client the URI of a response resource. The response can be the URI of the temporary status message, or the URI to some already existing, more permanent, resource.
Generally speaking, the 303 status code allows a REST API to send a reference to a resource without forcing the client to download its state. Instead, the client may send a GET request to the value of the Location header.
The 303 response MUST NOT be cached, but the response to the second (redirected) request might be cacheable.
304 (Not Modified)
This status code is similar to 204 (“No Content”) in that the response body must be empty. The critical distinction is that 204 is used when there is nothing to send in the body, whereas 304 is used when the resource has not been modified since the version specified by the request headers If-Modified-Since or If-None-Match.
In such a case, there is no need to retransmit the resource since the client still has a previously-downloaded copy.
Using this saves bandwidth and reprocessing on both the server and client, as only the header data must be sent and received in comparison to the entirety of the page being re-processed by the server, then sent again using more bandwidth of the server and client.
307 (Temporary Redirect)
A 307 response indicates that the REST API is not going to process the client’s request. Instead, the client should resubmit the request to the URI specified by the response message’s Location header. However, future requests should still use the original URI.
A REST API can use this status code to assign a temporary URI to the client’s requested resource. For example, a 307 response can be used to shift a client request over to another host.
The temporary URI SHOULD be given by the Location field in the response. Unless the request method was HEAD, the entity of the response SHOULD contain a short hypertext note with a hyperlink to the new URI(s). If the 307 status code is received in response to a request other than GET
or HEAD
, the user agent MUST NOT automatically redirect the request unless it can be confirmed by the user, since this might change the conditions under which the request was issued.
400 (Bad Request)
400 is the generic client-side error status, used when no other 4xx error code is appropriate. Errors can be like malformed request syntax, invalid request message parameters, or deceptive request routing etc.
The client SHOULD NOT repeat the request without modifications.
401 (Unauthorized)
A 401 error response indicates that the client tried to operate on a protected resource without providing the proper authorization. It may have provided the wrong credentials or none at all. The response must include a WWW-Authenticate header field containing a challenge applicable to the requested resource.
The client MAY repeat the request with a suitable Authorization header field. If the request already included Authorization credentials, then the 401 response indicates that authorization has been refused for those credentials. If the 401 response contains the same challenge as the prior response, and the user agent has already attempted authentication at least once, then the user SHOULD be presented the entity that was given in the response, since that entity might include relevant diagnostic information.
403 (Forbidden)
A 403 error response indicates that the client’s request is formed correctly, but the REST API refuses to honor it, i.e., the user does not have the necessary permissions for the resource. A 403 response is not a case of insufficient client credentials; that would be 401 (“Unauthorized”).
Authentication will not help, and the request SHOULD NOT be repeated. Unlike a 401 Unauthorized response, authenticating will make no difference.
404 (Not Found)
The 404 error status code indicates that the REST API can’t map the client’s URI to a resource but may be available in the future. Subsequent requests by the client are permissible.
No indication is given of whether the condition is temporary or permanent. The 410 (Gone) status code SHOULD be used if the server knows, through some internally configurable mechanism, that an old resource is permanently unavailable and has no forwarding address. This status code is commonly used when the server does not wish to reveal exactly why the request has been refused, or when no other response is applicable.
405 (Method Not Allowed)
The API responds with a 405 error to indicate that the client tried to use an HTTP method that the resource does not allow. For instance, a read-only resource could support only GET and HEAD, while a controller resource might allow GET and POST, but not PUT or DELETE.
A 405 response must include the Allow header, which lists the HTTP methods that the resource supports. For example:
Allow: GET, POST
406 (Not Acceptable)
The 406 error response indicates that the API is not able to generate any of the client’s preferred media types, as indicated by the Accept request header. For example, a client request for data formatted as application/xml
will receive a 406 response if the API is only willing to format data as application/json
.
If the response could be unacceptable, a user agent SHOULD temporarily stop receipt of more data and query the user for a decision on further actions.
412 (Precondition Failed)
The 412 error response indicates that the client specified one or more preconditions in its request headers, effectively telling the REST API to carry out its request only if certain conditions were met. A 412 response indicates that those conditions were not met, so instead of carrying out the request, the API sends this status code.
415 (Unsupported Media Type)
The 415 error response indicates that the API is not able to process the client’s supplied media type, as indicated by the Content-Type request header. For example, a client request including data formatted as application/xml
will receive a 415 response if the API is only willing to process data formatted as application/json
.
For example, the client uploads an image as image/svg+xml, but the server requires that images use a different format.
500 (Internal Server Error)
500 is the generic REST API error response. Most web frameworks automatically respond with this response status code whenever they execute some request handler code that raises an exception.
A 500 error is never the client’s fault, and therefore, it is reasonable for the client to retry the same request that triggered this response and hope to get a different response.
The API response is the generic error message, given when an unexpected condition was encountered and no more specific message is suitable.
501 (Not Implemented)
The server either does not recognize the request method, or it cannot fulfill the request. Usually, this implies future availability (e.g., a new feature of a web-service API).
References :
https://www.iana.org/assignments/http-status-codes/http-status-codes.xhtml
5xx — Server Error
This group of HTTP status codes indicates that the server is aware that it is on error or is incapable of performing the request. The server response usually includes an explanation of the error situation and if it is a temporary or permanent condition. These response codes in this group are applicable to any request method.
500 — Internal Server Error
The web server responds with this status code when it has encountered an unexpected condition, which prevented it from fulfilling the request by the client.
501 — Not Implemented
The web server responds with this status code when it does not support the functionality required to process the request. This is the appropriate response when the server does not recognize the request method and is not capable of supporting it for any resource.
502 — Bad Gateway
The server responds with this status code when, while acting as a gateway or proxy, it received an invalid response from the upstream server it accessed in attempting to process the request.
503 — Service Unavailable
The web server responds with this status code when it is currently unable to handle the request due to a temporary overloading or maintenance of the server. The implication is that this is a temporary condition, which will be alleviated after some delay. If known, the length of the delay may be indicated in a Retry-After header. If no Retry-After is given, the client should handle the response as it would for a 500 response.
504 — Gateway Timeout
The server, while acting as a gateway or proxy, did not receive a timely response from the upstream server specified by the request URL (e.g. HTTP, FTP, LDAP) or some other auxiliary server (e.g. DNS) it needed to access in attempting to complete the request.
505 — HTTP Version Not Supported
The web server responds with this status code when it does not support, or refuses to support, the HTTP protocol version that was used in the request message. The server is indicating that it is unable or unwilling to complete the request using the same major version as the client. The response should contain an entity describing why that version is not supported and what other protocols that server supports.
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