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

#define BUFFER_SIZE 1024

char *msg = "ack";

int main()
{
  char buffer[ BUFFER_SIZE ];

  int sock, newsock, len, fromlen, n, pid;

  /* socket structures from /usr/include/sys/socket.h */
  struct sockaddr_in server;
  struct sockaddr_in client;

  unsigned short port = 8127;

  /* Create the listener socket as TCP socket */
  /*   (use SOCK_DGRAM for UDP)               */
  sock = socket( PF_INET, SOCK_STREAM, 0 );

  if ( sock < 0 ) {
    perror( "socket()" );
    exit( 1 );
  }

  server.sin_family = PF_INET;
  server.sin_addr.s_addr = INADDR_ANY;

  /* htons() is host-to-network-short for marshalling */
  /* Internet is "big endian"; Intel is "little endian" */
  server.sin_port = htons( port );
  len = sizeof( server );

  if ( bind( sock, (struct sockaddr *)&server, len ) < 0 ) {
    perror( "bind()" );
    exit( 1 );
  }

  fromlen = sizeof( client );
  listen( sock, 5 );  /* 5 is number of backlogged waiting clients */
  printf( "Listener socket created and bound to port %d\n", port );

  while ( 1 ) {
    printf( "Blocked on accept()\n" );
    newsock = accept( sock, (struct sockaddr *)&client, &fromlen );
    printf( "Accepted client connection\n" );
fflush( NULL );

    /* handle socket in child process */
    pid = fork();
    if ( pid == 0 ) {
      /* can also use read() and write() */
      n = recv( newsock, buffer, BUFFER_SIZE - 1, 0 );
      if ( n < 1 ) {
        perror( "recv()" );
      }
      else {
        buffer[n] = '\0';
        printf( "Received message from %s: %s\n",
                inet_ntoa( (struct in_addr)client.sin_addr ),
                buffer );
      }
      n = send( newsock, msg, strlen( msg ), 0 );
      if ( n < strlen( msg ) ) {
        perror( "Write()" );
      }
      close( newsock );
      exit( 0 );
      /* child process becomes a zombie... */
    }

    /* parent simply closes the socket */
    close( newsock );
  }

  return 0; /* we never get here */
}