当浏览者访问一个网页时，浏览者的浏览器会向网页所在服务器发出请求。当浏览器接收并显示网页前，此网页所在的服务器会返回一个包含HTTP状态码的信息头（server header）用以响应浏览器的请求。
英文版
When a visitor visits a webpage, the browser of the visitor makes a request to the server where the webpage is located. When the browser receives and displays the web page, the server on which the web page resides returns a server header containing the HTTP status code to respond to the browser's request.
http常见的HTTP状态码：
200 - 请求成功
301 - 资源（网页等）被永久转移到其它URL
404 - 请求的资源（网页等）不存在
500 - 内部服务器错误
英文版
http common HTTP status code:
200 - The request was successful
301 - Resources (web pages, etc.) are permanently transferred to other URLs
404 - The requested resource (webpage, etc.) does not exist
500 - Internal server error
http状态码的分类
http状态码由三个十进制数字组成，第一个十进制数字定义了状态码的类型，后两个数字没有分类的作用。HTTP状态码共分为5种类型：分类描述
1**：信息，服务器收到请求，需要请求者继续执行操作
2**：成功，操作被成功接收并处理
3**：重定向，需要进一步的操作以完成请求
4**：客户端错误，请求包含语法错误或无法完成请求
5**：服务器错误，服务器在处理请求的过程中发生了错误
英文版
http status code classification
The http status code consists of three decimal digits. The first decimal digit defines the type of status code. The last two digits have no classification. HTTP status code is divided into 5 types: classification description
1 **: information, the server receives the request, the requester need to continue to operate
2 **: On success, the operation was successfully received and processed
3 **: Redirect, requires further action to complete the request
4 **: client error, request contains a syntax error or can not complete the request
5 **: server error, the server has encountered an error while processing the request
HTTP状态码表
100：继续。客户端应继续其请求
101：切换协议。服务器根据客户端的请求切换协议。只能切换到更高级的协议，例如，切换到HTTP的新版本协议
2开头的状态码
200：请求成功。一般用于GET与POST请求
201：已创建。成功请求并创建了新的资源
202：已接受。已经接受请求，但未处理完成
203：非授权信息。请求成功。但返回的meta信息不在原始的服务器，而是一个副本
204：无内容。服务器成功处理，但未返回内容。在未更新网页的情况下，可确保浏览器继续显示当前文档
205：重置内容。服务器处理成功，用户终端（例如：浏览器）应重置文档视图。可通过此返回码清除浏览器的表单域
206：部分内容。服务器成功处理了部分GET请求
3开头的状态码
300：多种选择。请求的资源可包括多个位置，相应可返回一个资源特征与地址的列表用于用户终端（例如：浏览器）选择
301：永久移动。请求的资源已被永久的移动到新URI，返回信息会包括新的URI，浏览器会自动定向到新URI。今后任何新的请求都应使用新的URI代替
302：临时移动。与301类似。但资源只是临时被移动。客户端应继续使用原有URI
303：查看其它地址。与301类似。使用GET和POST请求查看
304：未修改。所请求的资源未修改，服务器返回此状态码时，不会返回任何资源。客户端通常会缓存访问过的资源，通过提供一个头信息指出客户端希望只返回在指定日期之后修改的资源
305：使用代理。所请求的资源必须通过代理访问
306：已经被废弃的HTTP状态码
307：临时重定向。与302类似。使用GET请求重定向
4开头的状态码
400：客户端请求的语法错误，服务器无法理解
401：请求要求用户的身份认证
402：保留，将来使用
403：服务器理解请求客户端的请求，但是拒绝执行此请求
404：服务器无法根据客户端的请求找到资源（网页）。通过此代码，网站设计人员可设置"您所请求的资源无法找到"的个性页面
405：客户端请求中的方法被禁止
406：服务器无法根据客户端请求的内容特性完成请求
407：请求要求代理的身份认证，与401类似，但请求者应当使用代理进行授权
408：服务器等待客户端发送的请求时间过长，超时
409：服务器完成客户端的PUT请求是可能返回此代码，服务器处理请求时发生了冲突
410：客户端请求的资源已经不存在。410不同于404，如果资源以前有现在被永久删除了可使用410代码，网站设计人员可通过301代码指定资源的新位置
411：服务器无法处理客户端发送的不带Content-Length的请求信息
412：客户端请求信息的先决条件错误
413：由于请求的实体过大，服务器无法处理，因此拒绝请求。为防止客户端的连续请求，服务器可能会关闭连接。如果只是服务器暂时无法处理，则会包含一个Retry-After的响应信息
414：请求的URI过长（URI通常为网址），服务器无法处理
415：服务器无法处理请求附带的媒体格式
416：客户端请求的范围无效
417：服务器无法满足Expect的请求头信息
5开头的状态码
500；服务器内部错误，无法完成请求
501：服务器不支持请求的功能，无法完成请求
502：充当网关或代理的服务器，从远端服务器接收到了一个无效的请求
503：由于超载或系统维护，服务器暂时的无法处理客户端的请求。延时的长度可包含在服务器的Retry-After头信息中
504：充当网关或代理的服务器，未及时从远端服务器获取请求
505：务器不支持请求的HTTP协议的版本，无法完成处理
506：由《透明内容协商协议》（RFC 2295）扩展，代表服务器存在内部配置错误：被请求的协商变元资源被配置为在透明内容协商中使用自己，因此在一个协商处理中不是一个合适的重点。
507：服务器无法存储完成请求所必须的内容。这个状况被认为是临时的。WebDAV (RFC 4918)
509：服务器达到带宽限制。这不是一个官方的状态码，但是仍被广泛使用。
510：获取资源所需要的策略并没有没满足。（RFC 2774）
英文版
HTTP Status Code Table (Version 1)
100: continue. Clients should continue their request
101: Switch the protocol. The server switches the protocol according to the client's request. You can only switch to more advanced protocols, for example, to switch to the new version of HTTP
2 The beginning of the status code
200: The request was successful. Generally used for GET and POST requests
201: Created. Successfully requested and created new resource
202: Accepted. Already accepted the request but did not process it
203: unauthorized information. The request is successful. But the meta-information returned is not a copy of the original server, but a copy
204: No content. The server processed successfully but did not return content. Without updating the page, make sure that the browser continues to display the current document
205: Reset content. If the server is successfully processed, the user terminal (for example, browser) should reset the document view. This return code can be used to clear the browser's form fields
206: part of the content. The server successfully processed part of the GET request
3 at the beginning of the status code
300: a variety of options. The requested resource can include multiple locations, and a list of resource features and addresses can be returned accordingly for the user terminal (eg, browser) to select
301: move permanently. The requested resource has been permanently moved to the new URI, the returned information will include the new URI, and the browser will automatically redirect to the new URI. Any new requests in the future should use the new URI instead
302: temporary move. Similar to 301. But resources are only temporarily moved. The client should continue to use the original URI
303: View other addresses. Similar to 301. View using GET and POST requests
304: unmodified. The requested resource is unmodified, and the server does not return any resources when it returns this status code. Clients typically cache accessed resources by providing a header that states that the client wants to return only those resources that were modified after the specified date
305: Use a proxy. The requested resource must be accessed through a proxy
306: HTTP status code that has been discarded
307: temporary redirect. Similar to 302. Use GET request redirection
4 The beginning of the status code
400: Client request syntax error, the server can not understand
401: The request asks the user for authentication
402: Reserved for future use
403: The server understands the request for the client, but refuses to execute the request
404: The server could not find the resource (web page) based on the client's request. With this code, a website designer can set a personalized page that says "The resource you requested can not be found."
405: The method in the client request is disabled
406: The server can not complete the request based on the content characteristics requested by the client
407: The request asks for the identity of the proxy, similar to 401, but the requester should use the proxy for authorization
408: The server waits for the client to send the request for too long, timeout
409: The server may complete the client's PUT request is likely to return this code, the server encountered a request conflict
410: The client requested resource no longer exists. 410 is different from 404, if the resource has been permanently deleted for the 410 code, the site designer can specify the new location of the resource with the 301 code
411: The server was unable to process the request message sent by the client without Content-Length
412: Client request information is a prerequisite error
413: The request is denied because the requested entity is too large for the server to process. To prevent continuous client requests, the server may close the connection. If only the server temporarily unable to deal with, it will contain a Retry-After response
414: Request URI is too long (URI is usually the URL), the server can not handle
415: The server was unable to process the media format attached to the request
416: Invalid client request range
417: The server can not satisfy Expect's request header information
5 The beginning of the status code
500; internal server error, unable to complete the request
501: The server does not support the requested functionality and can not complete the request
502: A server acting as a gateway or proxy receives an invalid request from a remote server
503: The server is temporarily unable to process the client's request due to overloading or system maintenance. The length of the delay can be included in the server's Retry-After header
504: act as a gateway or proxy server, did not get requests from the remote server in time
505: The server does not support the requested version of the HTTP protocol and can not complete the process
506: Expanded by Transparent Content Negotiation Protocol (RFC 2295), representing an internal configuration error on behalf of the server: The requested Negotiation Argument resource is configured to use itself in transparent content negotiation and is therefore not suitable in a negotiation process Focus.
507: The server can not store the content necessary to complete the request. This situation is considered temporary. WebDAV (RFC 4918)
509: The server reached the bandwidth limit. This is not an official status code, but is still widely used.
510: The strategy needed to get the resource is not missing. (RFC 2774)
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