Detailed introduction to restful http

HTTP (HyperText Transfer Protocol) is a set of rules for computers to communicate through the network. Computer experts designed HTTP to enable HTTP clients (such as Web browsers) to request information and services from HTTP servers (Web servers). The current version of the HTTP protocol is 1.1. HTTP is a stateless protocol, and stateless refers to the Web There is no need to establish a persistent connection between the browser and the Web server. This means that when a client makes a request to the server and the Web server returns a response, the connection is closed and no information about the connection is retained on the server. Information.HTTP follows the request/response model. The web browser sends a request to the web server, and the web server processes the request and returns an appropriate response. All HTTP connections are structured as a set of requests and responses.

HTTP uses content types, which means that the files returned by the web server to the web browser have related types. All of these types are modeled on the MIME Internet Mail Protocol, which means that the web server tells the web browser what kind of file it is, whether it is an HTML document, a GIF image, a sound file, or a standalone application. Most Web browsers have a set of configurable helper applications that tell the browser how to handle various content types sent by the Web server.

The HTTP communication mechanism is that during a complete HTTP communication process, the following 7 steps will be completed between the web browser and the web server:

(1) Establish a TCP connection

Before HTTP work begins, the web browser must first establish a connection with the web server through the network. The connection is completed through TCP. This protocol and the IP protocol jointly build the Internet, the famous TCP/IP protocol family, so the Internet Also known as TCP/IP network. HTTP is a higher-level application layer protocol than TCP. According to the rules, only after the lower-layer protocol is established, the higher-layer protocol can be connected. Therefore, a TCP connection must be established first. Generally, the port number of the TCP connection is 80

(2) The web browser sends a request command to the web server

Once the TCP connection is established, the web browser will send a request command to the web server

For example: GET/sample/hello .jsp HTTP/1.1

(3) The Web browser sends the request header information

After the browser sends its request command, it also sends some other information to the Web server in the form of header information. , and then the browser sends a blank line to notify the server that it has finished sending the header information.

(4) Web server response

After the client sends a request to the server, the server will send a response back to the client,

HTTP/1.1 200 OK

The first part of the response is the protocol version number and response status code

(5) The Web server sends response header information

Just as the client will send information about itself along with the request, the server will also Along with the response, the user is sent data about itself and the requested document.

(6) The Web server sends data to the browser

After the Web server sends the header information to the browser, it will send a blank line to indicate that the sending of the header information ends here, and then , it sends the actual data requested by the user in the format described by the Content-Type response header information

(7) The Web server closes the TCP connection

Under normal circumstances, once the Web server sends a request to the browser After the server sends the request data, it will close the TCP connection, and then if the browser or server adds this line of code to its header information

Connection:keep-alive

After the TCP connection is sent will remain open so the browser can continue sending requests over the same connection. Keeping connections saves the time required to establish a new connection for each request and also saves network bandwidth.

　　

HTTP request format

When the browser makes a request to the Web server, it passes a data block to the server, which is the request information. The HTTP request information consists of 3 Part composition:

l Request method URI protocol/version

l Request header (Request Header)

l Request body

The following is an HTTP request Example:

GET/sample.jspHTTP/1.1

Accept:image/gif.image/jpeg,*/*

Accept-Language:zh-cn

Connection:Keep-Alive

Host:localhost

User-Agent:Mozila/4.0(compatible;MSIE5.01;Window NT5.0)

Accept- Encoding:gzip,deflate

username=jinqiao&password=1234

(1) Request method URI protocol/version

request The first line is "Method URL proposal/version": GET/sample.jsp HTTP/1.1

In the above code, "GET" represents the request method, "/sample.jsp" represents the URI, "HTTP/1.1

Represents the protocol and protocol version.

According to the HTTP standard, HTTP requests can use multiple request methods. For example: HTTP1.1 supports 7 request methods: GET, POST, HEAD, OPTIONS, PUT, DELETE and TARCE. In Internet applications, the most commonly used methods are GET and POST.

The URL completely specifies the network resource to be accessed, usually just giving a relative directory relative to the root directory of the server, so it always starts with "/", and finally, the protocol version declares the communication process version using HTTP.

(2) Request Header

The request header contains a lot of useful information about the client environment and the request body. For example, the request header can declare the language used by the browser, the length of the request body, etc.

Accept:image/gif.image/jpeg.*/*

Accept-Language:zh-cn

Connection:Keep-Alive

Host :localhost

User-Agent:Mozila/4.0(compatible:MSIE5.01:Windows NT5.0)

Accept-Encoding:gzip,deflate.

（3） Request body

There is a blank line between the request header and the request body. This line is very important. It indicates that the request header has ended, and what follows is the request body. The request body can contain the query string information submitted by the customer:

username=jinqiao&password=1234

In the above example of the HTTP request, the request body has only one line of content. Of course, in actual applications, the HTTP request body can contain more content.

HTTP request method I will only discuss the GET method and POST method here

l GET method

The GET method is the default HTTP request method. We use the GET method to submit forms every day. Data, however, the form data submitted using the GET method is only briefly encoded, and it will be sent to the Web server as part of the URL. Therefore, if you use the GET method to submit the form data, there are security risks. For example

Http://127.0.0.1/login.jsp?Name=zhangshi&Age=30&Submit=%cc%E+%BD%BB

From the above URL request, it is easy to Recognize the content of form submissions. (What follows?) In addition, since the data submitted by the GET method is part of the URL request, the amount of data submitted cannot be too large

l   POST method

The POST method is an alternative to the GET method Method, it mainly submits form data to the Web server, especially large batches of data. The POST method overcomes some of the shortcomings of the GET method. When submitting form data through the POST method, the data is not transmitted to the Web server as part of the URL request but as standard data. This overcomes the shortcomings of the GET method in which the information cannot be kept confidential and the data volume is too small. Therefore, for security reasons and respect for user privacy, the POST method is usually used when submitting forms.

From a programming perspective, if the user submits data through the GET method, the data is stored in the QUERY_STRING environment variable, while the data submitted by the POST method can be obtained from the standard input stream.

HTTP response is similar to HTTP request. HTTP response also consists of 3 parts, namely:

l Protocol status version code description

l Response header (Response Header)

l Response text

The following is an example of an HTTP response:

HTTP/1.1 200 OK
Server:Apache Tomcat/5.0.12
Date:Mon,6Oct2003 13:23:42 GMT
Content-Length:112