HTTP request headers and response headers (GET and post)

Introduction to HTTP

The HTTP protocol is an abbreviation for the Hyper Text Transfer Protocol (Hypertext Transfer Protocol), which is used to transfer hypertext to the local browser from the World Wide Web (www:world Wide Web) server.
HTTP is a TCP/IP communication protocol that transmits data (HTML files, image files, query results, and so on).

How HTTP Works

HTTP three-point considerations:

• HTTP is no connection: the meaning of no connection is to limit the processing of only one request per connection. When the server finishes processing the customer's request and receives the customer's answer, the connection is disconnected. In this way, the transmission time can be saved.
• HTTP is media Independent: This means that any type of data can be sent over HTTP as long as the client and the server know what to do with the data content. The client and server specify that the appropriate Mime-type content type be used.
• HTTP is stateless: The HTTP protocol is a stateless protocol. Stateless means that the protocol has no memory capacity for transactional processing. A lack of state means that if the previous information is required for subsequent processing, it must be re-routed, which may cause the amount of data to be transferred per connection to increase. On the other hand, it responds faster when the server does not need the previous information.

HTTP message structure HTTP request message

An HTTP request message consists of a request line, a request header (header), a blank line, and 4 parts of the request data, giving the general format of the request message.

1. Request Line

The request line consists of 3 fields of the Request Method field, the URL field, and the HTTP protocol version field, separated by a space. For example, get/index.html http/1.1.

HTTP requests can use a variety of request methods, depending on the HTTP standard.
HTTP1.0 defines three methods of request: GET, POST, and head.
HTTP1.1 has five new request methods: Options, PUT, DELETE, TRACE, and CONNECT methods.

And there are several common ones:

1). GET

The most common kind of request, when the client to read the document from the server, when clicked on a link on the Web page or through the browser's address bar to enter a URL to browse the Web page, the use of the Get method. The Get method requires the server to place the URL-positioned resource in the data portion of the response message, which is sent back to the client. When using the Get method, the request parameter and the corresponding value are appended to the URL, using a question mark ("?" ) represents the end of the URL and the start of the request parameter, which is limited by the length of the pass parameter. For example,/index.jsp?id=100&op=bind, so that data passed by get is directly represented in the address, so we can send the result of the request as a link to the friend. To use Google search Domety as an example, the request format is as follows:

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Get/search? hl=zh-cn&source=hp&q=domety&aq=f&oq= http/1.1
Accept:image/gif, Image/x-xbitmap, Image/jpeg, Image/pjpeg, Application/vnd.ms-excel, Application/vnd.ms-powerpoint ,
Application/msword, Application/x-silverlight, Application/x-shockwave-flash, */*
Referer: <a href="http://www.google.cn/">http://www.google.cn/</a>
Accept-language:zh-cn
Accept-encoding:gzip, deflate
user-agent:mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1;. NET CLR 2.0.50727; TheWorld)
Host: <a href="http://www.google.cn">www.google.cn</a>
Connection:keep-alive
Cookie: pref=id=80a06da87be9ae3c:u=f7167333e2c3b714: nw=1: tm=1261551909   : lm=1261551917: s=ybycq2wpfefs4v9g;
Nid=31=ojj8d-iygaetsxlgajmqsjvhcspkvijrb6omjamnrsm8lzhky_ ymfo2m4qmrkch1g0iqv9u-2hfbw7bufwvh7pgarub0rnhcju37y-
Fxlrugatx63jlv7cwmd6ub_o_r

as you can see, requests for Get methods generally do not contain the "Request Content" section, where the request data is expressed in the form of an address in the request line. The address links are as follows:

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1. <a href="http://www.google.cn/search?hl=zh-CN&source=hp&q=domety&aq=f&oq=" >http://www.google.cn/search? hl=zh-cn&source=hp
2. &q=domety&aq=f&oq=</a>

Address "?" The next part is the request data sent through GET, we can see clearly in the address bar, each data is separated by the "&" symbol. Obviously, this is not a good way to transfer private data. Also, because different browser-to-address character restrictions are also different, generally only up to 1024 characters can be recognized, so if you need to transfer large amounts of data, it is not appropriate to use the Get method.

2). POST

For cases where the Get method is not appropriate, consider using post, because using the Post method allows the client to provide more information to the server. The Post method encapsulates the request parameter in the HTTP request data, appears as a name/value, and can transmit a large amount of data so that the post does not have a limit on the size of the data being transmitted, and it is not displayed in the URL. Also take the above search Domety as an example, if you use the Post method, the format is as follows:

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Post/search http/1.1
Accept:image/gif, Image/x-xbitmap, Image/jpeg, Image/pjpeg, Application/vnd.ms-excel, Application/vnd.ms-powerpoint ,
Application/msword, Application/x-silverlight, Application/x-shockwave-flash, */*
Referer: <a href="http://www.google.cn/">http://www.google.cn/</a>
Accept-language:zh-cn
Accept-encoding:gzip, deflate
user-agent:mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1;. NET CLR 2.0.50727; TheWorld)
Host: <a href="http://www.google.cn">www.google.cn</a>
Connection:keep-alive
Cookie: pref=id=80a06da87be9ae3c:u=f7167333e2c3b714: nw=1: tm=1261551909   : lm=1261551917: s=ybycq2wpfefs4v9g;
Nid=31=ojj8d-iygaetsxlgajmqsjvhcspkvijrb6omjamnrsm8lzhky_ ymfo2m4qmrkch1g0iqv9u-2hfbw7bufwvh7pgarub0rnhcju37y-
Fxlrugatx63jlv7cwmd6ub_o_r
hl=zh-cn&source=hp&q=domety

As you can see, the POST request line does not contain a data string, which is stored in the Request Content section and is separated by the "&" symbol between the data. The Post method is mostly used for pages in forms. Because post can also do get function, so most people use the Post method when designing the form, in fact, this is a misunderstanding. Get mode also has its own characteristics and advantages, we should choose whether to use Get or post according to different circumstances.

3). HEAD

Head is like a get, except that the server receives a head request and returns only the response header, without sending the response content. When we only need to look at the state of a page, the use of head is very efficient, because the content of the page is omitted during transmission.

2. Request Header

The request header consists of a keyword/value pair, one pair per line, a keyword and a value separated by a colon ":". The request header notifies the server that there is information about the client request, and the typical request headers are:

• User-agent: The type of browser that generated the request.
• Accept: A list of content types that the client can identify.
• Host: The hostname of the request, which allows multiple domain names to be located in the same IP address as the virtual host.

3. Blank Line

The last request header is followed by a blank line that sends a carriage return and a newline character, notifying the server that the request header is no longer available.

4. Request data

The request data is not used in the Get method, but is used in the Post method. The Post method is useful for situations where a customer needs to fill out a form. The most commonly used request headers associated with request data are Content-type and content-length.

Instance

1). GET

Request First Line get/hello/index.jsp http/1.1 Request header information because the GET request has no body Host:localhost user-agent:mozilla/5.0 (Windows NT 5.1; rv:5.0) gecko/20100101 firefox/5.0 accept:text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 accept-language:zh-cn,zh;q=0.5 Accept-encoding:gzip, deflate accept-charset:gb2312,utf-8;q=0.7,*;q=0.7 Connection:keep-alive Cookie:jsessionid=369766fdf6220f7803433c0b2de36d98 Blank Line Because get has no body, the following is empty

2). POST

Request First Line post/hello/index.jsp http/1.1 Request header Information Host:localhost user-agent:mozilla/5.0 (Windows NT 5.1; rv:5.0) gecko/20100101 firefox/5.0 accept:text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 accept-language:zh-cn,zh;q=0.5 Accept-encoding:gzip, deflate accept-charset:gb2312,utf-8;q=0.7,*;q=0.7 Connection:keep-alive referer:http://localhost/hello/index.jsp Cookie:jsessionid=369766fdf6220f7803433c0b2de36d98 content-type:application/x-www-form-urlencoded Content-length:14 This is a blank line. Post has request body Username=hello

HTTP Response message

The HTTP response is also made up of three parts: the status line, the response header, the blank line, and the response body.
As you can see, the only real difference in response is that the first line uses state information instead of the request information. Status line describes the requested resource situation by providing a status code.

The status line format is as follows:

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1. Http-version Status-code reason-phrase CRLF

Where http-version represents the version of the server HTTP protocol;
Status-code indicates the response status code sent back by the server;
Reason-phrase represents a textual description of the status code.

HTTP status Code

When a viewer accesses a webpage, the browser of the viewer makes a request to the server where the page is located. When a Web page is received and displayed by the browser, the server on which the page resides returns a message header (server header) that contains the HTTP status code to respond to the browser's request.
HTTP status code in English is HTTP status code. The status code consists of three digits, the first number defines the category of the response, and there are five possible values.

• 1XX: Indicates that the request has been received and continues processing.
• 2XX: Success-Indicates that the request has been successfully received, understood, accepted.
• 3XX: Redirect--further action is required to complete the request.
• 4XX: Client Error--the request has a syntax error or the request is not implemented.
• 5XX: Server-side error-the server failed to implement a legitimate request.

A description of the common status code and status is described below.

• OK: Client request succeeded.
• Bad Request: Client requests have syntax errors and cannot be understood by the server.
• 401 Unauthorized: Request is not authorized, this status code must be used with the Www-authenticate header domain.
• 403 Forbidden: The server receives the request but refuses to provide the service.
• 404 Not Found: The request resource does not exist, for example: The wrong URL was entered.
• Internal Server error: Unexpected errors occurred on the server.
• 503 Server Unavailable: The server is currently unable to process client requests and may return to normal after a period of time, for example: http/1.1 OK (CRLF).

HTTP response Header

HTTP Content-type

Content-type, content type, generally refers to the presence of Content-type in a Web page, which defines the type of network file and the encoding of the Web page, and determines in what form and in what encoding the browser will read the file. This is the reason why you often see the results of a click on an ASP page that is downloaded to a file or a picture.

HTTP Content-type Table

About the difference between get and post for HTTP requests

1.GET submission, the requested data will be appended to the URL (that is, the data placed in the HTTP protocol header), in order to split the URL and transfer data, multiple parameters with & connection; for example: LOGIN.ACTION?NAME=HYDDD &password=idontknow&verify=%e4%bd%a0%E5%A5%BD. If the data is an English letter/number, sent as is, if it is a space, converted to +, if it is Chinese/other characters, the string is directly encrypted with BASE64, such as:%E4%BD%A0%E5%A5%BD, where the xx in%xx is the symbol in 16 binary notation ASCII.

Post submission: Place the submitted data in the packageof the HTTP packet. In the example above, the red font indicates the actual transfer data

As a result, the data submitted by get is displayed in the Address bar, while the post is submitted, the address bar does not change

2. The size of the transmitted data:

First, the HTTP protocol does not limit the size of the transmitted data, nor does the HTTP protocol specification limit the URL length. The main limitations in the actual development are:

GET: Specific browsers and servers have restrictions on URL length, such as IE's limit on URL length is 2083 bytes (2k+35). For other browsers, such as Netscape, Firefox, etc., there is theoretically no length limit, and its limitations depend on the support of the operating system.

Therefore, for a get commit, the transmitted data is limited by the URL length.

POST: The theoretical data is not limited because it is not transmitted via a URL. However, the actual Web server will be required to limit the size of the post submission data, Apache, IIS6 have their own configuration.

3. Security:

The security of post is higher than the security of get. Note: The security described here is not the same concept as the "security" mentioned in get above. The meaning of "security" above is simply not to make data changes, and the meaning of security here is the meaning of true security, such as: submit data through get, user name and password will appear in plaintext on the URL, because (1) the login page may be cached by the browser, (2) Other people to view the browser's history, Then someone else can get your account number and password,

HTTP request headers and response headers (GET and post)