Python chat--cgi

CGI is an interface standard between an external application (CGI program) and a Web server, which is the process of passing information between a CGI program and a Web server. The CGI specification allows the Web server to execute external programs and send their output to a Web browser, CGI turning a simple set of static hypermedia documents from the Web into a complete new interactive media.

The vast majority of CGI programs are used to interpret the input information from the form, to generate the appropriate processing on the server, or to feed the corresponding feedback to the browser. CGI programs make Web pages interactive.

The HTTP header format is as follows:

HTTP 字段名: 字段内容例如Content-type: text/html\r\n\r\n

The following table describes the frequently used information in the HTTP header in CGI programs:

Head	Description
Content-type:	The MIME information for the request that corresponds to the entity. Example: content-type:text/html
Expires:date	Date and time when the response expires
Location:url	Used to redirect the receiver to the location of the non-request URL to complete the request or identify the new resource
Last-modified:date	Requested last modified time for resource
Content-length:n	The requested content length
Set-cookie:string	Set HTTP Cookies

CGI Environment variables

All CGI programs receive the following environment variables, which play an important role in CGI programs:

Variable name	Description
Content_Type	The value of this environment variable indicates the MIME type of the information being passed. Currently, the environment variable content_type is generally: application/x-www-form-urlencoded, who says the data comes from an HTML form.
Content_length	If the server and CGI program information is passed as post, this environment variable can be read from the standard input stdin bytes of valid data. This environment variable must be used when reading the input data.
Http_cookie	The COOKIE content within the client.
Http_user_agent	Provides customer browser information that contains a version number or other proprietary data.
Path_info	The value of this environment variable represents the other path information immediately following the CGI program name. It often appears as a parameter to a CGI program.
Query_string	If the server and CGI program information is passed in a get, the value of this environment variable even if the information is passed. This information is followed by the CGI program name, with a question mark '? ' in between. Separated.
Remote_addr	The value of this environment variable is the IP address of the client sending the request, such as 192.168.1.67 above. This value is always present. And it is a unique identifier that Web clients need to provide to the Web server, which can be used in a CGI program to differentiate between different Web clients.
Remote_host	The value of this environment variable contains the host name of the client that sent the CGI request. If you do not support the query, you do not need to define this environment variable.
Request_method	Provides the method that the script is called. For scripts that use the http/1.0 protocol, only get and POST make sense.
Script_filename	The full path of the CGI script
Script_name	The name of the CGI script
server_name	This is the host name, alias, or IP address of your WEB server.
Server_software	The value of this environment variable contains the name and version number of the HTTP server that called the CGI program. For example, the value above is apache/2.2.14 (Unix)

Get and Post methods

The browser client passes information to the server in two ways, both the GET method and the POST method.

Using cookies in CGI

In the HTTP protocol a big drawback is not to make the user's identity judgment, so that the programmer to bring great inconvenience,

The advent of the cookie function compensates for this shortcoming.

All cookies are written on the client's hard drive through the client's browser while the client accesses the script, and when the next client accesses the script, it retrieves the data information, which is used in the password judgment.

　

The syntax of a cookie

HTTP cookie is sent through the HTTP header to achieve, he was earlier than the file transfer, the head Set-cookie syntax as follows:

< Code class= "Python functions" >set - cookie: Name = name;expires = date;path = path;domain = domain; Secure

• Name=name: The value of the cookie needs to be set (name cannot use ";" and ","), with multiple name values separated by ";" For example: Name1=name1;name2=name2;name3=name3.

• Expires=date:cookie expiration date, format: expires= "wdy,dd-mon-yyyy HH:MM:SS"

• Path=path: Sets the path supported by the cookie, if path is a path, then the cookie takes effect for all files and subdirectories in this directory, for example: Path= "/cgi-bin/", if path is a file, the cookie means that the file is in effect, For example: Path= "/cgi-bin/cookie.cgi".

• Domain=domain: The domain name that is valid for the cookie, for example: domain= "www.chinalb.com"

• Secure: If this flag is given, it means that the cookie can only be passed through an HTTPS server on the SSL protocol.

The receipt of a cookie is implemented by setting the environment variable Http_cookie, which can be retrieved by the CGI program to obtain cookie information.

Retrieving cookie Information

The Cookie Information retrieval page is very simple and the cookie information is stored in the CGI environment variable Http_cookie, which is stored in the following format:

key1 = value1;key2 = value2;key3 = value3....

Python chat--cgi