TCP socket simple sample.

tcp_server.c

//
//  main.c
//  os_base_socket
//
//  Created by xiangshouding on 14-7-13.
//  Copyright (c) 2014 xiangshouding. All rights reserved.
//

#include <stdio.h>
#include <stdlib.h>
/**
 * define `strerror`
 */
#include <string.h>
/**
 * define `ap_start` and `ap_end`
 */
#include <stdarg.h>
#include <unistd.h>
#include <errno.h>
/**
 * define `socket` `bind`
 */
#include <sys/socket.h>
/**
 * define `sockaddr`
 */
#include <netinet/in.h>

/**
 * define `htons` and `htonl`
 */
#include <arpa/inet.h>


/**
 * define `gethostbyaddr`
 */
#include <netdb.h>

void catch_error(int exit_code, const char *format, ...) {
    char *buf;
    va_list ap;
    va_start(ap, format);
    vasprintf(&buf, format, ap);
    fprintf(stderr, "%s errno: %d errmsg: %s\n", buf, errno, strerror(errno));
    va_end(ap);
    exit(exit_code);
}

int main(int argc, const char * argv[])
{
    int socket_fd;
    socklen_t len;
    struct in_addr in_addr;
    struct sockaddr_in server_addr;
    
    
    struct sockaddr_in client_addr;
    struct hostent *client_hostent;
    int client_len;
    int conn_fd;
   
    //init
    bzero((char *) & server_addr, sizeof(server_addr));
    
    in_addr.s_addr = htonl(INADDR_ANY); //listen any address. like is `0.0.0.0`
    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(4000); //port
    server_addr.sin_addr = in_addr;
    
    len = sizeof(server_addr);
    
    /**
     * AF_INET AF = address family, INET -> ip4
     * SOCK_STREAM -> TCP
     */
    socket_fd = socket(AF_INET, SOCK_STREAM, 0);
    
    if (-1 == socket_fd) {
        catch_error(1, "create socket fail: %d", socket_fd);
    }
    
    if (-1 == (bind(socket_fd, (const struct sockaddr *)&server_addr, len))) {
        close(socket_fd);
        catch_error(1, "bind address fail.");
    }
    
    if (-1 == (listen(socket_fd, 128))) {
        close(socket_fd);
        catch_error(1, "listen fail.");
    }
    
    for(;;) {
        client_len = sizeof(client_addr);
        if (-1 == (conn_fd = accept(socket_fd, (struct sockaddr *) &client_addr, (socklen_t *)&client_len))) {
            close(socket_fd);
            catch_error(1, "accpet fail");
        }
        
        client_hostent = gethostbyaddr((const char *)&client_addr.sin_addr.s_addr, sizeof(client_addr.sin_addr.s_addr), AF_INET);
        
        printf("conn %s %s\n", inet_ntoa(client_addr.sin_addr), client_hostent->h_name);
        
        write(conn_fd, "test\n", 6);
        
        close(conn_fd);
    }
    
    close(socket_fd);
    return -1;
}