CLIENT.C

/*
                                 Code Sample 25_1
*/

    /* client.c - code for example client program that uses TCP */

#ifndef unix
#define WIN32
#include <windows.h>
#include <winsock.h>
#else
#define closesocket close
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#endif

#include <stdio.h>
#include <string.h>

#define PROTOPORT       5193            /* default protocol port number */

    extern  int             errno;
    char    localhost[] =   "localhost";    /* default host name            */
    /*------------------------------------------------------------------------
     * Program:   client
     *
     * Purpose:   allocate a socket, connect to a server, and print all output
     *
     * Syntax:    client [ host [port] ]
     *
     *               host  - name of a computer on which server is executing
     *               port  - protocol port number server is using
     *
     * Note:      Both arguments are optional.  If no host name is specified,
     *            the client uses "localhost"; if no protocol port is
     *            specified, the client uses the default given by PROTOPORT.
     *
     *------------------------------------------------------------------------
     */
    main(argc, argv)
    int     argc;
    char    *argv[];
    {
            struct  hostent  *ptrh;  /* pointer to a host table entry       */
            struct  protoent *ptrp;  /* pointer to a protocol table entry   */
            struct  sockaddr_in sad; /* structure to hold an IP address     */
            int     sd;              /* socket descriptor                   */
            int     port;            /* protocol port number                */
            char    *host;           /* pointer to host name                */
            int     n;               /* number of characters read           */
            char    buf[1000];       /* buffer for data from the server     */
#ifdef WIN32
            WSADATA wsaData;
            WSAStartup(0x0101, &wsaData);
#endif
            memset((char *)&sad,0,sizeof(sad)); /* clear sockaddr structure */
            sad.sin_family = AF_INET;         /* set family to Internet     */

            /* Check command-line argument for protocol port and extract    */
            /* port number if one is specified.  Otherwise, use the default */
            /* port value given by constant PROTOPORT                       */

            if (argc > 2) {                 /* if protocol port specified   */
                    port = atoi(argv[2]);   /* convert to binary            */
            } else {
                    port = PROTOPORT;       /* use default port number      */
            }
            if (port > 0)                   /* test for legal value         */
                    sad.sin_port = htons((u_short)port);
            else {                          /* print error message and exit */
                    fprintf(stderr,"bad port number %s\n",argv[2]);
                    exit(1);
            }

            /* Check host argument and assign host name. */

            if (argc > 1) {
                    host = argv[1];         /* if host argument specified   */
            } else {
                    host = localhost;
            }

            /* Convert host name to equivalent IP address and copy to sad. */

            ptrh = gethostbyname(host);
            if ( ((char *)ptrh) == NULL ) {
                    fprintf(stderr,"invalid host: %s\n", host);
                    exit(1);
            }
            memcpy(&sad.sin_addr, ptrh->h_addr, ptrh->h_length);

            /* Map TCP transport protocol name to protocol number. */

            if ( ((int)(ptrp = getprotobyname("tcp"))) == 0) {
                    fprintf(stderr, "cannot map \"tcp\" to protocol number");
                    exit(1);
            }

            /* Create a socket. */

            sd = socket(PF_INET, SOCK_STREAM, ptrp->p_proto);
            if (sd < 0) {
                    fprintf(stderr, "socket creation failed\n");
                    exit(1);
            }

            /* Connect the socket to the specified server. */

            if (connect(sd, (struct sockaddr *)&sad, sizeof(sad)) < 0) {
                    fprintf(stderr,"connect failed\n");
                    exit(1);
            }

            /* Repeatedly read data from socket and write to user's screen. */

            n = recv(sd, buf, sizeof(buf), 0);
            while (n > 0) {
                    write(1,buf,n);
                    n = recv(sd, buf, sizeof(buf), 0);
            }

            /* Close the socket. */

            closesocket(sd);

            /* Terminate the client program gracefully. */

            exit(0);
    }