echod.c

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

#define MSG "EchoD (v0.1): What you send me - I send you back!\n"

static int sock, conn;

int handle_reply(char *str)
{
   char response[64] = {0};

   send(conn, "You said: ", 10, 0);

   sprintf(response, str);
   send(conn, response, 64, 0);

   return 0;
}

int main(int argc, char * argv[])
{
   struct sockaddr_in my_addr, client_addr;
   int sockopt_on = 1;
   int optval;
   int sa_in_size = sizeof(struct sockaddr_in);
   char reply[2048];

   // Get a socket
   if((sock = socket(AF_INET, SOCK_STREAM,0)) == -1)
   {
      perror("socket");
      exit(1);
   }

   // First zero the struct
   memset((char *) &my_addr, 0, sa_in_size);

   // Now fill in the fields we need
   my_addr.sin_family = AF_INET;
   my_addr.sin_port = htons(atoi(argv[1]));
   my_addr.sin_addr.s_addr = htonl(INADDR_ANY);

   optval = 1;
   setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &optval, sizeof(optval));
   
   // Bind our socket to the port
   if(bind(sock,(struct sockaddr *)&my_addr, sa_in_size) == -1)
   {
      perror("bind");
      exit(1);
   }

   // Start listening for incoming connections
   if(listen(sock, 0) == -1)
   {
      perror("listen");
      exit(1);
   }

   while(1)
   {
      memset(reply, 0x00, 2048);

      // Grab connections
      conn = accept(sock, (struct sockaddr *)&client_addr, &sa_in_size);
      if(conn == -1)
      {
         perror("accept");
         exit(1);
      }

      // Send a greeting
      send(conn, MSG, strlen(MSG), 0);

      while(recv(conn, reply, 2048, 0))
      {
         handle_reply(reply);
      }

   }

   return 0;
}