Old snippet from back in the day.

echoserver.c

/*
  * @Author       tjhv
  * @Version      1.0.1
  * @year         2009
  **/

#include <arpa/inet.h>
#include <netinet/in.h>
#include <stdio.h>
#include <string.h>
#include <sys/param.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <unistd.h>
#include <stdarg.h>

struct ServerEngine
{
          int sockfd;
          struct sockaddr_in s;
          int port;
          int eid;
          int backlog;
          signed char isActive;
};

struct ClientEngine
{
          int sockfd;
          struct sockaddr_in s;
          int eid;
          size_t len;
          char *ip;
};

int create_sockfd(struct ServerEngine serverEngine)
{
          serverEngine.sockfd = socket(AF_INET, SOCK_STREAM, 0);
          return serverEngine.sockfd;
}

struct sockaddr_in create_struct(struct ServerEngine serverEngine)
{
          serverEngine.s.sin_family = AF_INET;
          serverEngine.s.sin_port = htons(serverEngine.port);
          serverEngine.s.sin_addr.s_addr = htonl(INADDR_ANY);
          return serverEngine.s;
}

int _bind(struct ServerEngine serverEngine)
{
          serverEngine.eid = bind(serverEngine.sockfd, (struct sockaddr *) &serverEngine.s, sizeof(serverEngine.s));
          return serverEngine.eid;
}

int _listen(struct ServerEngine serverEngine)
{
          serverEngine.eid = listen(serverEngine.sockfd, serverEngine.backlog);
          return serverEngine.eid;
}

int _send(struct ClientEngine clientEngine, char *buf, ...)
{
          char buff[1024];
          va_list ap;
          va_start(ap, buf);
          vsprintf(buf, buf, ap);
          va_end(ap);
          clientEngine.eid = send(clientEngine.sockfd, buff, strlen(buff), 0);
          return clientEngine.eid;
}

void _run(struct ServerEngine serverEngine)
{
          while (serverEngine.isActive)
                  {
                            struct ClientEngine clientEngine;
                            clientEngine.len = sizeof(clientEngine.s);
                            clientEngine.eid = accept(serverEngine.sockfd, (struct sockaddr *) &clientEngine.s, &clientEngine.len);
                            if (clientEngine.eid >= 0)
                                    {
                                              clientEngine.sockfd = clientEngine.eid;
                                              clientEngine.ip = inet_ntoa(clientEngine.s.sin_addr);
                                              _send(clientEngine, "Your IP Address is %s.\r\n", clientEngine.ip);
                                              /* Check if the IP is banned using CIDR. If so, close the connection. */
                                              /* Assign a slot for the client and pass it to the Engine. */
                                              close(clientEngine.sockfd);
                                            }
                          }
}

int main(void)
{
          /* Need to make a better method for this? Perhaps it shouldn't be in the main function.. */
          struct ServerEngine s;
          s.port = 40000;
          s.backlog = 3;
          s.isActive = 1;
          create_sockfd(s);
          create_struct(s);
          _bind(s);
          _listen(s);
          _run(s);
          return 0;
}