Sunday, April 26, 2020

Simple Web Client Program

We are going to attempt a simple web client program.  We request a webpage from "yahoo.com".  Get the IP Address using ping command.  It is "98.137.246.7".  Use it in the program.

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[root@svtap01end1 work]# ping yahoo.com
PING yahoo.com (98.137.246.7) 56(84) bytes of data.
64 bytes from media-router-fp1.prod1.media.vip.gq1.yahoo.com (98.137.246.7): icmp_seq=1 ttl=51 time=265 ms
64 bytes from media-router-fp1.prod1.media.vip.gq1.yahoo.com (98.137.246.7): icmp_seq=2 ttl=51 time=265 ms
64 bytes from media-router-fp1.prod1.media.vip.gq1.yahoo.com (98.137.246.7): icmp_seq=3 ttl=51 time=265 ms


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#include <stdio.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <string.h>

int main(int argc, char const *argv[])
{
 int sock;

 // Create a socket
 if ((sock = socket(AF_INET,SOCK_STREAM,0))<0) {
  printf("socket creation error\n");
  return -1;
 }

 
 struct sockaddr_in serv_addr;
 serv_addr.sin_family=AF_INET;
 serv_addr.sin_port=htons(80);
 
 // Convert IP Address in binary format
 if(inet_pton(AF_INET,"98.137.246.7",&serv_addr.sin_addr) <= 0) {
  printf("Address conversion to binary\n");
  return -1;
 }

 // Connect client socket to the web server
 if(connect(sock,(struct sockaddr *)&serv_addr,sizeof(serv_addr)) <0)
 {
  printf("Connection Error\n");
  return -1;
 }

 // Request for a web page by sending HTTP Get Packet
 if(write(sock, "GET / HTTP/1.1\r\n\r\n",strlen("GET / HTTP/1.1\r\n\r\n")) != strlen("GET / HTTP/1.1\r\n\r\n"))
 {
  printf("Error write\n");
  return -1;
 }

 char recvline[80];
 memset(recvline,0,80); //Fill all 80 characters to 0
 int i,readlen,linecounter=1;
 
 // Read the characters in batches of 80
 while ((readlen=read(sock,recvline,80)) >0)
 {
  printf("%d  -",linecounter);
  
  //Carriage Return and New Line Character has to be displayed as it is
  for (i=0; i<readlen; i++) { 
   if (recvline[i] == '\n') {
    printf("\\n");
   } else if (recvline[i] == '\r') {
     printf("\\r");
   } else {
    printf("%c",recvline[i]);
   }
  }
  linecounter++;
  printf("\n");
 }

 //Close the socket
 close(sock);
 printf("Successful creation");
 return 0;
}

Regular steps involved in creating a socket:

Line 11 - Creating a socket.  Stream Socket as HTTP involves TCP.
Line 22 - IP Address to be copied in the binary format
Line 28 - Connect to yahoo server with the port 80

Retrieving Data will be:

Line 35 - Send a HTTP Get packet to retrieve a web page
Line 46 - Loop to retrieve characters in the batches of 80
Line 52 - Carriage Return and New Line Characters has to be displayed as \r and \n

Close the connection:

Line 65 - Close the socket

When executed, Line Batch number and the Contents are displayed as


# gcc -o webclient webclient.c
# ./webclient
1  -HTTP/1.1 400 Host Header Required\r\nDate: Sun, 26 Apr 2020 16:48:32 GMT\r\nConnecti
2  -on: close\r\nServer: ATS\r\nCache-Control: no-store\r\nContent-Type: text/html\r\nConten
3  -t-Language: en\r\nX-Frame-Options: SAMEORIGIN\r\nContent-Length: 4383\r\n\r\n<!DOCTYPE h
4  -tml>\n<html lang="en-us">\n  <head>\n    <meta http-equiv="content-type" content="t
5  -ext/html; charset=UTF-8">\n    <meta charset="utf-8">\n    <title>Yahoo</title>\n
6  -  <meta name="viewport" content="width=device-width,initial-scale=1,minimal-ui">
7  -\n    <meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1">\n    <style>\n
8  -      html {\n          height: 100%;\n      }\n      body {\n          background:
9  -#fafafc url(https://s.yimg.com/nn/img/sad-panda-201402200631.png) 50% 50%;\n
10  -     background-size: cover;\n          height: 100%;\n          text-align: cente
11  -r;\n          font: 300 18px "helvetica neue", helvetica, verdana, tahoma, arial,
12  - sans-serif;\n          margin: 0;\n      }\n      table {\n          height: 100%;\n
13  -          width: 100%;\n          table-layout: fixed;\n          border-collapse:
14  - collapse;\n          border-spacing: 0;\n          border: none;\n      }\n      h1
15  - {\n          font-size: 42px;\n          font-weight: 400;\n          color: #4000
16  -90;\n      }\n      p {\n          color: #1A1A1A;\n      }\n      #message-1 {\n
17  -     font-weight: bold;\n          margin: 0;\n      }\n      #message-2 {\n
18  -  display: inline-block;\n          *display: inline;\n          zoom: 1;\n
19  -  max-width: 17em;\n          _width: 17em;\n      }\n      </style>\n      <script>
20  -\n      \n      </script>\n  </head>\n  <body>\n  <!-- status code : 400 -->\n  <!-- H
21  -ost Header Required -->\n  <!-- host machine: media-router-fp1001.prod.media.gq1.
22  -yahoo.com -->\n  <!-- timestamp: 1587919712.936 -->\n  <!-- url: http:///-->\n  <sc
23  -ript type="text/javascript">\n    function buildUrl(url, parameters){\n      var q
24  -s = [];\n      for(var key in parameters) {\n        var value = parameters[key];\n
25  -        qs.push(encodeURIComponent(key) + "=" + encodeURIComponent(value));\n
26  -  }\n      url = url + "?" + qs.join('&');\n      return url;\n    }\n\n    function
27  -generateBRBMarkup(site) {\n      params.source = 'brb';\n      generateBeaconMarku
28  -p(params);\n      var englishHeader = 'Will be right back...';\n      var englishM
29  -essage1 = 'Thank you for your patience.';\n      var englishMessage2 = 'Our engin
30  -eers are working quickly to resolve the issue.';\n      var defaultLogoStyle = ''
31  -;\n      var siteDataMap = {\n        'default': {\n          logo: 'https://s.yimg
32  -.com/rz/p/yahoo_frontpage_en-US_s_f_p_205x58_frontpage.png',\n          logoAlt:
33  -'Yahoo Logo',\n          logoStyle: defaultLogoStyle,\n          header: englishHe
34  -ader,\n          message1: englishMessage1,\n          message2: englishMessage2\n
35  -       }\n      };\n\n      var siteDetails = siteDataMap['default'];\n\n      docume
36  -nt.write('<table><tbody><tr><td>');\n      document.write('<div id="content">');\n
37  -      document.write('<img src="' + siteDetails['logo'] + '" alt="' + siteDetail
38  -s['logoAlt'] + '" style="' + siteDetails['logoStyle'] + '">');\n      document.wr
39  -ite('<h1 style="margin-top:20px;">' + siteDetails['header'] + '</h1>');\n      do
40  -cument.write('<p id="message-1">' + siteDetails['message1'] + '</p>');\n      doc
41  -ument.write('<p id="message-2">' + siteDetails['message2'] + '</p>');\n      docu
42  -ment.write('</div>');\n      document.write('</td></tr></tbody></table>');\n    }\n
43  -\n    function generateBeaconMarkup(params) {\n        document.write('<img src="'
44  - + buildUrl('//geo.yahoo.com/b', params) + '" style="display:none;" width="0px"
45  -height="0px"/>');\n        var beacon = new Image();\n        beacon.src = buildUr
46  -l('//bcn.fp.yahoo.com/p', params);\n    }\n\n    var hostname = window.location.hos
47  -tname;\n    var device = '-';\n    var ynet = ('-' === '1');\n    var time = new Da
48  -te().getTime();\n    var params = {\n        s: '1197757129',\n        t: time,\n
49  -     err_url: document.URL,\n        err: '400',\n        test: '-',\n        ats_h
50  -ost: 'media-router-fp1001.prod.media.gq1.yahoo.com',\n        rid: '-',\n        m
51  -essage: 'Host Header Required'\n    };\n\n    if(ynet) {\n        document.write('<d
52  -iv style="height: 5px; background-color: red;"></div>');\n    }\n    generateBRBMa
53  -rkup(hostname, params);\n\n  </script>\n  <noscript>\n  <table>\n    <tbody>\n      <t
54  -r>\n        <td>\n          <div id="englishContent">\n            <h1 style="margi
55  -n-top:20px;">Will be right back...</h1>\n            <p id="message-1">Thank you
56  -for your patience.</p>\n            <p id="message-2">Our engineers are working q
57  -uickly to resolve the issue.</p>\n          </div>\n        </td>\n      </tr>\n
58  -</tbody>\n  </table>\n  </noscript>\n  </body>\n</html>\n
Successful creation
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