tcp_client.c

/*
 * tcpclient.c - A simple TCP client
 * usage: tcpclient <host> <port>
 */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>

#define BUFSIZE 1024

/*
 * error - wrapper for perror
 */
void error(char *msg) {
    perror(msg);
    exit(0);
}

int main(int argc, char **argv) {
    int sockfd, portno, n;
    struct sockaddr_in serveraddr;
    struct hostent *server;
    char *hostname;
    char buf[BUFSIZE];

    /* check command line arguments */
    if (argc != 3) {
       fprintf(stderr,"usage: %s <hostname> <port>\n", argv[0]);
       exit(0);
    }

    hostname = argv[1];
    portno = atoi(argv[2]);

    /* socket: create the socket */
    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd < 0)
        error("ERROR opening socket");

    /* gethostbyname: get the server's DNS entry */
    server = gethostbyname(hostname);
    if (server == NULL) {
        fprintf(stderr,"ERROR, no such host as %s\n", hostname);
        exit(0);
    }

    /* build the server's Internet address */
    bzero((char *) &serveraddr, sizeof(serveraddr));
    serveraddr.sin_family = AF_INET;
    bcopy((char *)server->h_addr,
	  (char *)&serveraddr.sin_addr.s_addr, server->h_length);
    serveraddr.sin_port = htons(portno);

    /* connect: create a connection with the server */
    if (connect(sockfd, (struct sockaddr *) &serveraddr, sizeof(serveraddr)) < 0)
      error("ERROR connecting");


    for (int i = 0; i < 10; i++) {
        /* send the message line to the server */
        buf[0] = 'A' + i;
        buf[1] = 'A' + i;
        buf[2] = 'A' + i;
        buf[3] = 'A' + i;
        buf[4] = '\0';

        printf("sending: '%.*s'\n", (int) strlen(buf), buf);

        n = write(sockfd, buf, strlen(buf));
        if (n < 0)
          error("ERROR writing to socket");

        sleep(1);
    }

    close(sockfd);
    return 0;
}