Network-Programming-in-C/examples/tcp_client.c

/*
* client.c -- a stream socket client demo
*/

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

#include <arpa/inet.h>

#define PORT "3490"    // the port client will be connecting to

#define MAXDATASIZE 100  // max number of bytes we can get at once

//get sockaddr, IPv4 or IPv6:
void *get_in_addr(struct sockaddr *sa){
    
    if(sa->sa_family == AF_INET){
        return &(((struct sockaddr_in*)sa)->sin_addr);
    }

    return &(((struct sockaddr_in6*)sa)->sin6_addr);
}

int main(int argc, char *argv[]){
    int sockfd, numbytes;
    char buf[MAXDATASIZE];
    struct addrinfo hints, *servinfo, *p;
    int rv;
    char s[INET6_ADDRSTRLEN];

    if(argc != 2){
        fprintf(stderr, "usage: client hostname\n");
        exit(1);
    }


    memset(&hints, 0, sizeof hints);
    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = SOCK_STREAM;

    if((rv = getaddrinfo(argv[1], PORT, &hints, &servinfo)) != 0){
        fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
        return 1;
    }

    // loop through all the results and connect to the first we can
    for( p = servinfo; p != NULL ; p = p->ai_next){
        if((sockfd = socket(p->ai_family, p->ai_socktype,
                        p->ai_protocol)) == -1){
            perror("client: socket");
            continue;
        }

        if(connect(sockfd, p->ai_addr, p->ai_addlen) == -1){
            close(sockfd);
            perror("client: connect");
            continue;
        }

        break;
    }

    if( p == NULL ){
        fprintf(stderr, "client: failed to connect\n");
        return 2;
    }


    inet_ntop(p->ai_family, get_in_addr((struct sockaddr *)p->ai_addr),
                s, sizeof s);

    printf("client: connecting to %s\n", s);

    freeaddrinfo(servinfo); // all done with this structure

    if((numbytes = recv(sockfd, buf, MAXDATASIZE-1, 0)) == -1){
        perror("recv");
        exit(1);
    }

    buf[numbytes] = '\0';

    printf("client: received '%s' \n", buf);

    close(sockfd);

    return 0;
}