Examples of connection-oriented client/server communications

The following two program examples illustrate how a streams connection in the Internet domain is initialized by the client and accepted by the server: 

Example 1: Initialization of a streams connection by the client

#include <sys.types.h>
#include <sys.socket.h>
#include <netinet.in.h>
#include <netdb.h> 
#include <stdio.h>
#include <stdlib.h>
#define DATA "Half a league, half a league . . ."
  
/*
 * This program creates a socket and initializes a connection with the 
 * Internet address passed in the command line.
 * A message is sent via the connection.
 * The socket is then closed and the connection shut down. 
 * The client program expects the entry of a host name and 
 * port number. It is the host on which the server program runs and 
 * the port number of the list socket of the server program (in the example 
 * the port number 2222). 
 */
  
main(argc, argv)
      int argc;
      char *argv[];
{
      int sock;
      struct sockaddr_in server;
      struct hostent *hp; 
      /* Create a socket */
      sock = socket(AF_INET, SOCK_STREAM, 0);
      if (sock < 0) {
              perror("opening stream socket");
              exit(1);
      }
  
      /* Connection setup using the name specified in the 
       * command line. 
       */
      server.sin_family = AF_INET;
      hp = gethostbyname(argv[1]);
      if (hp == 0) {
              fprintf(stderr, "%s: unknown host\n", argv[1]);
              exit(2);
      }
      memcpy((char *)&server.sin_addr, (char *)hp->h_addr,
        hp->h_length);
      server.sin_port = htons(atoi(argv[2]));
      if (connect(sock, (struct sockaddr*)&server, sizeof server) < 0) {
              perror("connecting stream socket");
              exit(1);
      }
      if (send(sock, DATA, sizeof DATA, 0) < 0)
              perror("writing on stream socket");
      soc_close(sock);
      exit(0);
}

Example 2: Acceptance of the streams connection by the server

#include <sys.types.h>
#include <sys.socket.h>
#include <netinet.in.h>
#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#define TRUE 1
#define TESTPORT 2222
/*
 * This program creates a socket and then goes into an endless loop. 
 * With each loop run, it accepts a connection and sends messages. 
 * If the connection is interrupted or a termination message is passed,
 * the program accepts a new connection.
 */

main()
{
      int sock, length;
      struct sockaddr_in server, client;
      int msgsock;
      char buf[1024];
      int rval;
      /* Create socket. */
      sock = socket(AF_INET, SOCK_STREAM, 0);
      if (sock < 0) {
              perror("opening stream socket");
              exit(1);
      }
/* The socket is assigned a name using wildcards. */
      server.sin_family = AF_INET;
      server.sin_addr.s_addr = htonl(INADDR_ANY);
      server.sin_port = htons(TESTPORT);
      if (bind(sock, (struct sockaddr*)&server, sizeof server ) < 0) {
              perror("binding stream socket");
              exit(1);
      }
      /* Start acceptance of connection requests. */
      listen(sock, 5);
      do {
              length = sizeof client;
              msgsock = accept(sock, (struct sockaddr*)&client, &length);
              if (msgsock == -1)
                      perror("accept");
              else do {
                      memset(buf, 0, sizeof buf );
                      if ((rval = recv(msgsock, buf, 1024, 0)) < 0)
                              perror("reading stream message");
                 else if (rval == 0)
                              printf("Ending connection\n");
                      else
                              printf("-->%s\n", buf); } 
              while (rval > 0);
              soc_close(msgsock);
      } while (TRUE);

      /*
       * As this program runs in an endless loop, the socket "sock" is 
       * never explicitly closed. 
       * However, all sockets are closed automatically if a task is
       * terminated or reaches its normal conclusion.
       */

       exit(0);
}