HTTP 狀態碼表明一個 HTTP 要求是否已經被完成。回應分為五種：
- 資訊回應 (Informational responses,
- 成功回應 (Successful responses,
- 重定向 (Redirects,
- 用戶端錯誤 (Client errors,
- 伺服器端錯誤 (Server errors,
- 請求成功。成功的意義依照 HTTP 方法而定：
POST：已傳送訊息主體中的 resource describing the result of the action。
- 請求成功且新的資源成功被創建，通常用於 POST 或一些 PUT 請求後的回應。
- 此請求已經被接受但尚未處理。此狀態為非承諾性，代表 HTTP 無法在之後傳送一個非同步的回應告知請求的處理結果。最初目的為外部程序或其他伺服器處理請求的情況，或用於批次處理中。
203 Non-Authoritative Information
- 此回應碼表示回傳的中介資料集與並非與原始伺服器上的有效確定集合完全相同，而是來自本地或第三方的副本。除此情況外，200 OK 回應碼應該被優先使用。
204 No Content
- There is no content to send for this request, but the headers may be useful. The user-agent may update its cached headers for this resource with the new ones.
205 Reset Content
- This response code is sent after accomplishing request to tell user agent reset document view which sent this request.
206 Partial Content
- This response code is used because of range header sent by the client to separate download into multiple streams.
- A Multi-Status response conveys information about multiple resources in situations where multiple status codes might be appropriate.
- Used inside a DAV: propstat response element to avoid enumerating the internal members of multiple bindings to the same collection repeatedly.
226 IM Used(HTTP Delta encoding)
- 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.
300 Multiple Choice
301 Moved Permanently
- 此回應碼的意思是，請求資源的 URI 已被改變。有時候，會在回應內給予新的 URI。
- This response code means that URI of requested resource has been changed temporarily. New changes in the URI might be made in the future. Therefore, this same URI should be used by the client in future requests.
303 See Other
- Server sent this response to directing client to get requested resource to another URI with an GET request.
304 Not Modified
- This is used for caching purposes. It is telling to client that response has not been modified. So, client can continue to use same cached version of response.
305 Use Proxy
- 在舊版本的 HTTP 規範中，表示請求資源必須透過代理存取。基於對代理的頻內設置 (in-band configuration) 相關的安全考量，該狀態碼已棄用。
- 該狀態碼已不再被使用，僅被保留。該狀態碼曾在先前得的 HTTP 1.1 規範中被使用。
307 Temporary Redirect
- 伺服器發送此回應來使客戶端保持請求方法不變向新的地址發出請求。 與
308 Permanent Redirect
- This means that the resource is now permanently located at another URI, specified by the
Location:HTTP Response header. This has the same semantics as the
301 Moved PermanentlyHTTP response code, with the exception that the user agent must not change the HTTP method used: if a
POSTwas used in the first request, a
POSTmust be used in the second request.
400 Bad Request
- 需要授權以回應請求。它有點像 403，但這裡的授權，是有可能辦到的。
402 Payment Required
- 用戶端並無訪問權限，例如未被授權，所以伺服器拒絕給予應有的回應。不同於 401，伺服端知道用戶端的身份。
404 Not Found
405 Method Not Allowed
406 Not Acceptable
- This response is sent when the web server, after performing server-driven content negotiation, doesn't find any content following the criteria given by the user agent.
407 Proxy Authentication Required
- This is similar to 401 but authentication is needed to be done by a proxy.
408 Request Timeout
- This response is sent on an idle connection by some servers, even without any previous request by the client. It means that the server would like to shut down this unused connection. This response is used much more since some browsers, like Chrome, Firefox 27+, or IE9, use HTTP pre-connection mechanisms to speed up surfing. Also note that some servers merely shut down the connection without sending this message.
- This response would be sent when requested content has been deleted from server.
411 Length Required
412 Precondition Failed
- The client has indicated preconditions in its headers which the server does not meet.
413 Payload Too Large
414 URI Too Long
- 客戶端的 URI 請求超過伺服器願意解析的長度。
415 Unsupported Media Type
416 Requested Range Not Satisfiable
- The range specified by the
Rangeheader field in the request can't be fulfilled; it's possible that the range is outside the size of the target URI's data.
417 Expectation Failed
- This response code means the expectation indicated by the
Expectrequest header field can't be met by the server.
418 I'm a teapot
- The server refuses the attempt to brew coffee with a teapot.
421 Misdirected Request
- The request was directed at a server that is not able to produce a response. This can be sent by a server that is not configured to produce responses for the combination of scheme and authority that are included in the request URI.
422 Unprocessable Entity(WebDAV)
- The request was well-formed but was unable to be followed due to semantic errors.
424 Failed Dependency(WebDAV)
426 Upgrade Required
- The server refuses to perform the request using the current protocol but might be willing to do so after the client upgrades to a different protocol. The server sends an
Upgradeheader in a 426 response to indicate the required protocol(s).
428 Precondition Required
- 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.
429 Too Many Requests
- 用戶在給定的時間內 ("rate limiting") 發送了過多的請求。
431 Request Header Fields Too Large
451 Unavailable For Legal Reasons
500 Internal Server Error
501 Not Implemented
- The request method is not supported by the server and cannot be handled. The only methods that servers are required to support (and therefore that must not return this code) are
502 Bad Gateway
- This error response means that the server, while working as a gateway to get a response needed to handle the request, got an invalid response.
503 Service Unavailable
- The server is not ready to handle the request. Common causes are a server that is down for maintenance or that is overloaded. Note that together with this response, a user-friendly page explaining the problem should be sent. This responses should be used for temporary conditions and the
Retry-After:HTTP header should, if possible, contain the estimated time before the recovery of the service. The webmaster must also take care about the caching-related headers that are sent along with this response, as these temporary condition responses should usually not be cached.
504 Gateway Timeout
- This error response is given when the server is acting as a gateway and cannot get a response in time.
505 HTTP Version Not Supported
- 請求使用的 HTTP 版本不被伺服器支援。
506 Variant Also Negotiates
- The server has an internal configuration error: transparent content negotiation for the request results in a circular reference.
507 Insufficient Storage
- 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 end point in the negotiation process.
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
- The 511 status code indicates that the client needs to authenticate to gain network access.
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