Jose Solares

Note:This code expects to be using sockets blocking I/O request, to use non blocking I/O we should use libevent or a similar solution (like threads), this is outside of the scope of this code. It also assumes that we already have the server listening on a port and that we have already accepted a client connection `cliente_socket`. RCVBUFFER is 256.

char buffer[RCVBUFFER + 2];
buffer[RCVBUFFER] = 0;
char response[] = {2,6,1,0,7,1,0,2,1,6,0x81};
int  message_size,i,j;
char counter = 0;

if (( message_size = recv(client_socket, buffer,
        RCVBUFFER, 0)) < 0 )
   err_handler ("recv() failed");

if ( message_size == 17 ) {
   if ( send(client_socket, response, 11, 0) != 11 )
      err_handler ("send() failed");
} else {
   printf ( "- %d - \n", message_size );
   err_handler ("Protocol Error");
}

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

for (;;) {
   if (( message_size = recv(client_socket, buffer,
         RCVBUFFER, 0)) < 0 )
      err_handler ("recv() failed");

   if (message_size > 5 &amp;&amp; bufer[0] == -128)
      counter = buffer[3];
   i = (buffer[0] == -128)? 5 : 0;
   buffer[message_size + 1] = '\0';
   buffer[message_size] = '\n';

   //printf ("Capturing %d bytes\n",message_size);
   fprintf (stderr, "%s",&amp;buffer[i]);
   //printf ("Current Counter : %d\n",counter);

   if (message_size == 1) {
       if (buffer[0] == 0x50) {
          char respond[] = {0x51};
          if ( send (client_socket, respond, 1, 0) != 1)
          err_handler("send() failed");
      }
   } else {
      i = message_size - 1;
      if (buffer[i-2] == 0x20 &amp;&amp; buffer[i-1] == 0x0d &amp;&amp; 
          buffer[i] == 0x0a) {
         char respond[] = {0x40, 0x05, 0x01, ++counter, 0x81};
         if ( send (client_socket, respond, 5, 0) != 5 )
            err_handler("send() failed");
      }
   }
/* Do Something with the Data we received */
}