HTTP协议相关介绍

时间：2010-09-08 来源：near

　　HTTP is the protocol that allows web servers and browsers to send and receive data over the Internet. It is a request and response protocol. The client requests a file and the server responds to the request. HTTP uses reliable TCP connections—by default on TCP port 80.

1。 HTTP Requests

　　An HTTP request consists of three components:

Method—Uniform Resource Identifier (URI)—Protocol/Version
Request headers
Entity body

　　for example：

POST /examples/default.jsp HTTP/1.1
Accept: text/plain; text/html 
Accept-Language: en-gb Connection: 
Keep-Alive Host: localhost 
User-Agent: Mozilla/4.0 (compatible; MSIE 4.01; Windows 98) 
Content-Length: 33 
Content-Type: application/x-www-form-urlencoded 
Accept-Encoding: gzip, deflate 

lastName=Franks&firstName=Michael

　　The method—URI—protocol version appears as the first line of the request.

POST /examples/default.jsp HTTP/1.1

　　where POST is the request method, /examples/default.jsp represents the URI and HTTP/1.1 the Protocol/Version section.

　　Each HTTP request can use one of the many request methods as specified in the HTTP standards. The HTTP 1.1 supports seven types of request: GET, POST, HEAD, OPTIONS, PUT, DELETE, and TRACE. GET and POST are the most commonly used in Internet applications.

　　The URI specifies an Internet resource completely. A URI is usually interpreted as being relative to the server's root directory. Thus, it should always begin with a forward slash /. A Uniform Resource Locator (URL) is actually a type of URI (see http://www.ietf.org/rfc/rfc2396.txt). The protocol version represents the version of the HTTP protocol being used.

　　The request header contains useful information about the client environment and the entity body of the request. For example, it could contain the language the browser is set for, the length of the entity body, and so on. Each header is separated by a carriage return/linefeed (CRLF) sequence.

　　Between the headers and the entity body, there is a blank line (CRLF) that is important to the HTTP request format. The CRLF tells the HTTP server where the entity body begins. In some Internet programming books, this CRLF is considered the fourth component of an HTTP request.

　　In the previous HTTP request, the entity body is simply the following line:

lastName=Franks&firstName=Michael

The entity body can easily become much longer in a typical HTTP request.

2。HTTP Responses

　　Similar to an HTTP request, an HTTP response also consists of three parts:

Protocol—Status code—Description
Response headers
Entity body

for example：

HTTP/1.1 200 OK 
Server: Microsoft-IIS/4.0 
Date: Mon, 5 Jan 2004 13:13:33 GMT 
Content-Type: text/html 
Last-Modified: Mon, 5 Jan 2004 13:13:12 GMT 
Content-Length: 112 

<html>
　　<head>
　　　　<title>HTTP Response Example</title>
　　</head>
　　<body>
　　　　Welcome to Brainy Software
　　</body>
</html>

　　The first line of the response header is similar to the first line of the request header. The first line tells you that the protocol used is HTTP version 1.1, the request succeeded (200 = success), and that everything went okay.

　　The response headers contain useful information similar to the headers in the request. The entity body of the response is the HTML content of the response itself. The headers and the entity body are separated by a sequence of CRLFs.