socket.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <arpa/inet.h>

#define BACKLOG 5
#define BUF_SIZE 256

void error(char *msg)
{
    perror(msg);
    exit(EXIT_FAILURE);
}

int server_setup(void)
{
    int server_fd;
    struct sockaddr_in server;
    struct in_addr address;
    int size = sizeof(server);
    int opt = 1;

    if ((server_fd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
        error("Couldn't create socket");
    }

    if (setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt)) == -1) {
        error("Couldn't set socket options");
    }

    address.s_addr = INADDR_ANY;

    server.sin_family = AF_INET;
    server.sin_port   = htons(1234);
    server.sin_addr   = address;

    if (bind(server_fd, (struct sockaddr *) &server, (socklen_t) size) == -1) {
        error("Couldn't bind socket");
    }

    if (listen(server_fd, BACKLOG) == -1) {
        error("Couldn't listen");
    }

    return server_fd;
}

int accept_client(int server_fd)
{
    int client_fd;
    struct sockaddr_in client;
    int size = sizeof(client);

    if ((client_fd = accept(server_fd, (struct sockaddr *) &client, (socklen_t *) &size)) == -1) {
        error("Couldn't accept client");
    }

    fprintf(stderr, "A client has arrived from %s port %d\n", inet_ntoa(client.sin_addr), ntohs(client.sin_port));

    return client_fd;
}

void handle_client(client_fd)
{
    char buffer[BUF_SIZE];
    int count;
    char prefix[]  = "You said: ";
    char goodbye[] = "Goodbye!\r\n";

    while (1) {
        count = read(client_fd, buffer, BUF_SIZE);

        if (count == -1) {
            perror("Bad read from client");
            return;
        }
        else if (count == 0) {
            /* client closed the connection */
            close(client_fd);
        }

        buffer[count] = '\0';

        if (!strcmp(buffer, "quit\r\n")) {
            write(client_fd, goodbye, strlen(goodbye));
            close(client_fd);
            return;
        }

        write(client_fd, prefix, strlen(prefix));
        write(client_fd, buffer, count);
    }
}

int main()
{
    int server_fd, client_fd;

    server_fd = server_setup();

    while (1) {
        client_fd = accept_client(server_fd);
        handle_client(client_fd);
    }

    close(server_fd);

    printf("Exiting...\n");

    return 0;
}