摘要：HTTP status codes reference
HTTP status codes are extensible. HTTP applications are not required to understand the meaning of all registered status codes, though such understanding is obviously desirable. However, applications MUST understand the class of any status code, as indicated by the first digit, and treat any unrecognized response as being equivalent to the x00 status code of that class, with the exception that an unrecognized response MUST NOT be cached. For example, if an unrecognized status code of 431 is received by the client, it can safely assume that there was something wrong with its request and treat the response as if it had received a 400 status code. In such cases, user agents SHOULD present to the user the entity returned with the response, since that entity is likely to include human readable information which will explain the unusual status.
HTTP status codes are returned by web servers to indicate the status of a request. Codes 200 and 304 are used to tell the browser the page can be viewed. All other codes register hits and traffic that is unseen by the visitor. For example, a return code 301 or 302 will tell the browser to ask another page.
The following table outlines all status codes defined for the HTTP/1.1 draft specification outlined in IETF rfc 2068. They are 3-digit codes where the first digit identifies the class of the status code and the final digits correspond to the specific condition within the response class.
1xx class - Informational
Informational status codes are provisional responses from the web server; they give the client a heads-up on what the server is doing. Informational codes do not indicate an error condition.
100 Continue
The continue status code tells the browser to continue sending a request to the server.
101 Switching Protocols
The server sends this response when the client asks to switch from HTTP/1.0 to HTTP/1.1
2xx class - Successful
This class of status code indicates that the client's request was received, understood, and successful.
200 Successful
201 Created
202 Accepted
203 Non-Authorative Information
204 No Content
205 Reset Content
206 Partial Content
The partial content success code is issued when the server fulfills a partial GET request. This happens when the client is downloading a multi-part document or part of a larger file.
3xx class - Redirection
This code tells the client that the browser should be redirected to another URL in order to complete the request. This is not an error condition.
300 Multiple Choices
301 Moved Permanently
302 Moved Temporarily
303 See Other
304 Not Modified
305 Use Proxy
4xx class - Client Error
This status code indicates that the client has sent bad data or a malformed request to the server. Client errors are generally issued by the webserver when a client tries to gain access to a protected area using a bad username and password.
400 Bad Request
401 Unauthorized
402 Payment Required
403 Forbidden
404 Not Found
405 Method Not Allowed
406 Not Acceptable
407 Proxy Authentication Required
408 Request Timeout
409 Conflict
410 Gone
411 Length Required
412 Precondition Failed
413 Request Entity Too Long
414 Request-URI Too Long
415 Unsupported Media Type
5xx class - Server Error
This status code indicates that the client's request couldn't be succesfully processed due to some internal error in the web server. These error codes may indicate something is seriously wrong with the web server.
500 Internal Server Error
An internal server error has caused the server to abort your request. This is an error condition that may also indicate a misconfiguration with the web server. However, the most common reason for 500 server errors is when you try to execute a script that has syntax errors.
501 Not Implemented
This code is generated by a webserver when the client requests a service that is not implemented on the server. Typically, not implemented codes are returned when a client attempts to POST data to a non-CGI (ie, the form action tag refers to a non-executable file).
502 Bad Gateway
The server, when acting as a proxy, issues this response when it receives a bad response from an upstream or support server.
503 Service Unavailable
The web server is too busy processing current requests to listen to a new client. This error represents a serious problem with the webserver (normally solved with a reboot).
504 Gateway Timeout
Gateway timeouts are normally issued by proxy servers when an upstream or support server doesn't respond to a request in a timely fashion.
505 HTTP Version Not Supported
The server issues this status code when a client tries to talk using an HTTP protocol that the server doesn't support or is configured to ignore.
related reference:http://www.seoconsultants.com/w3c/status-codes/reason-phrases.asp
