Um simples client TCP

client.c

#include <signal.h>
#include <string.h>
#include <stdio.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netdb.h>
#include <stdlib.h>
#include <unistd.h>

#define MAX_LINE 1024

int open_clientfd(char *hostname, char *port) {
    int clientfd, rc;
    struct addrinfo hints, *listp, *p;

    memset(&hints, 0, sizeof(struct addrinfo));
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_flags = AI_NUMERICSERV;
    hints.ai_flags |= AI_ADDRCONFIG;
    if ((rc = getaddrinfo(hostname, port, &hints, &listp)) != 0) {
        fprintf(stderr, "Error connecting to server: %s\n", gai_strerror(rc));
        exit(1);
    }

    for (p = listp; p; p = p->ai_next) {
        if ((clientfd = socket(p->ai_family, p->ai_socktype, p->ai_protocol)) < 0) {
            continue;
        }

        if (connect(clientfd, p->ai_addr, p->ai_addrlen) != -1) {
            break; // The connection was successful, and we break
        }

        close(clientfd);
    }

    freeaddrinfo(listp);

    if (!p) { // None of the connections was successful
        return -1;
    } else {
        return clientfd;
    }
}

int main(int argc, char **argv) {
    if (argc < 3) {
        printf("Usage: %s <host> <port>", argv[0]);
    }

    int clientfd = open_clientfd(argv[1], argv[2]);
    if (clientfd == -1) {
        puts("Unable to connect to server");
        exit(1);
    }

    char res[MAX_LINE];
    char input[MAX_LINE] = "oi";
    pid_t pid;
    int input_pos = 0;

    if ((pid = fork()) == 0) { // child process
        while(1) {
            if (read(clientfd, res, MAX_LINE) <= 0 ) {
                puts("Server disconnected");
                kill(-pid, SIGINT);
            };
            printf("\n");
            printf("guest> %s", res);
            memset(res, 0, MAX_LINE);
        }
    } else {
        while(1) {
            fgets(input, MAX_LINE, stdin);
            printf("\033[A\r\033[K"); // clears the input so we can print the message below
            printf("you> %s", input);
            write(clientfd, input, strlen(input));
        }
    }
}