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Introduction and simple application of CGI

2022-07-22 03:06:00 【Amos_ zh】

What is? CGI?

CGI Is a common gateway interface (Common Gateway Interface); yes HTTP The server communicates with other programs “ conversation ” Tools for , adopt CGI Interface can run other programs on the server .CGI Is any standard input 、 Output 、 Executable file written and generated by the language of environment variables .

CGI Processing steps

Send the user request to the server through the browser
The server receives the user request and delivers it CGI process
CGI The program transmits the processing results to the server
The server sends the results back to the browser

CGI Programming

CGI The program is entered through standard (stdin)、 standard output (stdout) Realization and web Information transmission between servers
The environment variable is Web The server and CGI Agreed between interfaces , Used to direct to CGI The program passes some important parameters

CGI Transmit to Web The information of the server can be in various formats , Usually with HTML Text or XML The form of text

 （1） transmission HTML, The output of the first line of text must be "content-type:text/html\n\n"
 （2） transmission XML, The output of the first line of text must be ”content-type:text/xml\n\n”
 （3） There are other formats ：JIF(image/gif)、JPEG(image/jpeg)、AVI(video/avi)

Two important CGI environment variable :

QUERY_STRING： On the browser side, click GET Method input data , The content of the data is url Content after question mark

// Data can be read directly 
char *data = getenv("QUERY_STRING");//data-->"10+20"

CONTENT_LENGTH： On the browser side, click POST The number of bytes of data entered by the method , The content of the data is obtained through standard input

//1、 First, the length of the data 
char *len = getenv("CONTENT_LENGTH");
//2、 According to the length   From standard input device   Get content 
char data[128]="";
fgets(data,atoi(len)+1, stdin);//"10+20"

Case study ：cgi Implement calculator （GET Asynchronously ）

demo1.html

<html>
    <head>
        <title></title>
        <meta charset="utf-8"> 
        <script type="text/javascript" src="./js01.js"></script> 
    </head>
    <body>
        data1: <input type="text"  id="data1">
        <br>
        data2: <input type="text"  id="data2">
        <br>
        result: <label id="label"></label>
        <br>
        <input type="button" value="add" onclick="my_calc(0);">
        &nbsp;&nbsp;&nbsp;&nbsp;
        <input type="button" value="sub" onclick="my_calc(1);">
    </body>
</html>

js01.js

function getXMLHttpRequest()
{
    
    var xmlhttp = null;
    if (window.XMLHttpRequest)// Automatically detect the version of the current browser , If it is IE5.0 More than the higher version of the browser 
    {
    // code for IE7+, Firefox, Chrome, Opera, Safari
        xmlhttp=new XMLHttpRequest();// Create request object 
    }
    else If the browser is the bottom version 
    {
    // code for IE6, IE5
        xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");// Create request object 
    }
    return xmlhttp;// Return the request object 
}
function my_calc(arg)
{
    
   
    var data1 = document.getElementById("data1").value;
    var data2 = document.getElementById("data2").value;
    if(data1.length == 0 || data2.length == 0)
    {
    
        alert("data1  or  data2 Can't be empty ");
        return;
    }
    if(isNaN(data1) || isNaN(data2))
    {
    
        alert(" Please enter a valid number ");
        document.getElementById("data1").value = "";
        document.getElementById("data2").value = "";
        return;
    }
    var url = "";
    url += "cgi-bin/cgi_calc?"
    url += data1;
    if(arg == 0)
    {
    
        url += "+";
    }    
    else if(arg == 1)
    {
    
        url += "-";
    }
    url += data2;
    
    // obtain xmlhttprequest object 
    var xmlhttp = getXMLHttpRequest();

    // Set the callback function of the server asynchronous response 
    xmlhttp.onreadystatechange = function(){
    
        document.getElementById("label").innerHTML = xmlhttp.responseText;
    }

    //  Create server request 
    xmlhttp.open("get", url, true);

    //  Send server request 
    xmlhttp.send();
}

cgi_calc.c

#include <stdio.h>
#include <stdlib.h>

int main()
{
    
    // transmission HTML  The output of the first line of text must be "content-type:text/html\n\n"
    printf("content-type:text/html\n\n");

    // Get server data  GET The way  QUERY_STRING
    char *data = getenv("QUERY_STRING");//data = "10+20"
    int data1=0,data2=0;
    char ch = 0;
    sscanf(data, "%d%c%d", &data1, &ch, &data2);
    if(ch == '+')
    {
    
        printf("%d\n", data1+data2);
    }
    else if(ch == '-')
    {
    
        printf("%d\n", data1-data2);
    }
    
    return 0;
}