Http 简明教程

HTTP - Messages

HTTP基于客户端-服务器体系结构模型和无状态请求/响应协议，该协议通过在可靠的TCP/IP连接上交换消息来运行。

HTTP is based on the client-server architecture model and a stateless request/response protocol that operates by exchanging messages across a reliable TCP/IP connection.

HTTP“客户端”是一个程序（Web浏览器或任何其他客户端），用于建立与服务器的连接以发送一个或多个HTTP请求消息。HTTP“服务器”是一个程序（通常是类似Apache Web服务器或Internet信息服务IIS之类的Web服务器），通过发送HTTP响应消息来接受连接以响应HTTP请求。

An HTTP "client" is a program (Web browser or any other client) that establishes a connection to a server for the purpose of sending one or more HTTP request messages. An HTTP "server" is a program ( generally a web server like Apache Web Server or Internet Information Services IIS, etc. ) that accepts connections in order to serve HTTP requests by sending HTTP response messages.

HTTP 使用统一资源标识符 (URI) 来标识给定资源并建立连接。一旦建立了连接， HTTP messages 将会以类似于 Internet 邮件 [RFC5322] 和多用途 Internet 邮件扩展 (MIME) [RFC2045] 所使用的方式传递。这些消息包括从客户端到服务器的 requests 和从服务器到客户端的 responses ，它们将具有以下格式：

HTTP makes use of the Uniform Resource Identifier (URI) to identify a given resource and to establish a connection. Once the connection is established, HTTP messages are passed in a format similar to that used by the Internet mail [RFC5322] and the Multipurpose Internet Mail Extensions (MIME) [RFC2045]. These messages include requests from client to server and responses from server to client which will have the following format:

 HTTP-message   = <Request> | <Response> ; HTTP/1.1 messages

HTTP 请求和 HTTP 响应使用 RFC 822 的通用消息格式来传输所需的数据。此通用消息格式由以下四个项目组成。

HTTP requests and HTTP responses use a generic message format of RFC 822 for transferring the required data. This generic message format consists of the following four items.

A Start-line
Zero or more header fields followed by CRLF
An empty line (i.e., a line with nothing preceding the CRLF)
indicating the end of the header fields
Optionally a message-body

在以下章节中，我们将解释 HTTP 消息中使用的每个实体。

In the following sections, we will explain each of the entities used in an HTTP message.

Message Start-Line

起始行将具有以下通用语法：

A start-line will have the following generic syntax:

start-line = Request-Line | Status-Line

在讨论 HTTP 请求和 HTTP 响应消息时，我们将分别讨论请求行和状态行。现在，让我们看请求和响应情况下的起始行示例：

We will discuss Request-Line and Status-Line while discussing HTTP Request and HTTP Response messages respectively. For now, let’s see the examples of start line in case of request and response:

GET /hello.htm HTTP/1.1     (This is Request-Line sent by the client)

HTTP/1.1 200 OK             (This is Status-Line sent by the server)

Header Fields

HTTP 头字段提供关于请求或响应所需的信息，或关于在消息正文中发送的对象的信息。有四种类型的 HTTP 响应消息头：

HTTP header fields provide required information about the request or response, or about the object sent in the message body. There are four types of HTTP message headers:

  1. General-header: These header fields have general applicability for both request and response messages.

  2. Request-header: These header fields have applicability only for request messages.

  3. Response-header: These header fields have applicability only for response messages.

  4. Entity-header: These header fields define meta information about the entity-body or, if no body is present, about the resource identified by the request.

所有上述标头都遵循相同的通用格式，每个标头字段都包含一个名称，后跟冒号 ( : ) 和字段值，如下所示：

All the above mentioned headers follow the same generic format and each of the header field consists of a name followed by a colon (:) and the field value as follows:

message-header = field-name ":" [ field-value ]

以下是各種標頭欄位的範例：

Following are the examples of various header fields:

User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
Host: www.example.com
Accept-Language: en, mi
Date: Mon, 27 Jul 2009 12:28:53 GMT
Server: Apache
Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
ETag: "34aa387-d-1568eb00"
Accept-Ranges: bytes
Content-Length: 51
Vary: Accept-Encoding
Content-Type: text/plain

Message Body

HTTP 消息的消息主体部分是可选的，但如果有消息主体，则将其用于携带与请求或响应相关的主体。如果关联了主体，则通常 Content-Type 和 Content-Length 标头行指定关联主体的性质。

The message body part is optional for an HTTP message but if it is available, then it is used to carry the entity-body associated with the request or response. If entity body is associated, then usually Content-Type and Content-Length headers lines specify the nature of the body associated.

主体是实际承载 HTTP 请求数据（包括表单数据和上传的数据等）和来自服务器的 HTTP 响应数据（包括文件、图像等）的主体。下面显示了主体内容的示例：

A message body is the one which carries the actual HTTP request data (including form data and uploaded, etc.) and HTTP response data from the server ( including files, images, etc.). Shown below is the simple content of a message body:

<html>
   <body>

      <h1>Hello, World!</h1>

   </body>
</html>

接下来的两章将利用上述概念来准备 HTTP 请求和 HTTP 响应。

Next two chapters will make use of above explained concepts to prepare HTTP Requests and HTTP Responses.