Here is a small C program using the Berkeley Sockets API to communicate
with a web server via TCP/IP. It connects to a given server, sends a very
simple http request and retrieves the resulting response for displaying
it to the user. Control characters in the web server output are shown in
the form $xx (for example $d for ASCII 13, which is CR).

Not quite fancy or well-written, but at least a starter for libsocket use.


shell/iX> cat webreq.c

/*
  simple socket client. lars appel 15.nov.98
  connects to web server and requests data.

  usage: webreq ip-addr port "HEAD /urlpart"
         webreq ip-addr port "GET /urlpart"

  example: webreq 127.0.0.1 80 "HEAD /"
*/

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

main(int argc, char *argv[]) 
{
  int sd;
  struct sockaddr_in sa;
  int ret;

  char buf[4096];
  int len;
  int k;

  int port;

  if (argc < 2)
    { printf ("missing target ip\n"); exit (5); }
  else
    printf ("using target ip %s\n", argv[1]);

  if (argc < 3)
    { printf ("missing target port\n"); exit (6); }
  else {
    port = atoi (argv[2]);
    printf ("using target port %i\n", port);
  }

  if (argc < 4)
    { printf ("missing request string\n"); exit (7); }
  else
    printf ("using request string %s\n", argv[3]);

  sd = socket (AF_INET, SOCK_STREAM, IPPROTO_TCP);
  if (sd == -1) exit (1);

  sa.sin_family = AF_INET;
  sa.sin_addr.s_addr = inet_addr(argv[1]);
  sa.sin_port = port;

  ret = connect (sd, &sa, sizeof(sa));
  if (ret != 0) exit (2);

  strcpy (buf, argv[3]); 
  strcat (buf, " HTTP/1.0\r\n\r\n");

  printf ("actual request sent is %s", buf);

  len = send (sd, buf, strlen(buf), 0);
  if (len == -1) exit (3);

  len = recv (sd, buf, sizeof(buf), 0);
  if (len == -1) exit (4);

  close (sd);

  for (k = 0; k < len; k++) {
    if (buf[k] >= 32 && buf[k] < 127)
      printf ("%c",buf[k]);
    else if (buf[k] == '\n')
      printf ("\n");
    else
      printf (" $%x ",buf[k]);
  }
}


Here we compile with c89 and libsocket.a -- GNU gcc should also work.

shell/iX> c89 -D_POSIX_SOURCE -D_SOCKET_SOURCE webreq.c -lsocket -o webreq
 
shell/iX> ls -l

total 255
-rwxrwx---   1 LARS.APPEL        APPEL     126720 Apr 30 18:45 webreq
-rw-r-----   1 LARS.APPEL        APPEL       1510 Apr 30 18:42 webreq.c
-rw-rw----   1 LARS.APPEL        APPEL       2048 Apr 30 18:45 webreq.o


And now let's see two examples for using this little program, the first one
gets a positive response, the second one gets a negative response from the
web server (because the specified web page was not found)...

shell/iX> webreq 12.34.56.78 8008 "HEAD /index.html"

using target ip 12.34.56.78
using target port 8008
using request string HEAD /index.html
actual request sent is HEAD /index.html HTTP/1.0

HTTP/1.1 200 OK $d 
Date: Sun, 30 Apr 2000 16:49:15 GMT $d 
Server: Apache/1.3.9 (MPE/iX) ApacheJServ/1.1 $d 
Last-Modified: Sat, 25 Mar 2000 15:48:08 GMT $d 
ETag: "4788-3a2-38dcdfb8" $d 
Accept-Ranges: bytes $d 
Content-Length: 930 $d 
Connection: close $d 
Content-Type: text/html $d 
 $d 

shell/iX> webreq 12.34.56.78 8008 "HEAD /nonsense.txt"

using target ip 12.34.56.78
using target port 8008
using request string HEAD /nonsense.txt
actual request sent is HEAD /nonsense.txt HTTP/1.0

HTTP/1.1 404 Not Found $d 
Date: Sun, 30 Apr 2000 16:49:45 GMT $d 
Server: Apache/1.3.9 (MPE/iX) ApacheJServ/1.1 $d 
Connection: close $d 
Content-Type: text/html $d 
 $d 

shell/iX> exit