//==================================================== file = rawServer.c =====
//=  A message "server" program to demonstrate raw sockets programming        =
//=============================================================================
//=  Notes:                                                                   =
//=    1) This program compiles only for Winsock                              =
//=    2) This program serves a message to program rawClient running on       =
//=       another host.                                                       =
//=    3) For Windows 7 needs to run in an elevated command window (cmd)      =
//=---------------------------------------------------------------------------=
//=  Example execution: (rawServer and rawClient running on host 127.0.0.1)   =
//=   Waiting for recvfrom() to complete...                                   =
//=   IP address of client = 127.0.0.1                                        =
//=   Received from client: 4500003755ae000080ff00007f0000017f000001 | Test   =
//=   message from CLIENT to SERVER                                           =
//=---------------------------------------------------------------------------=
//=  Build: bcc32 rawClient.c ws2_32.lib or cl rawClient.c ws2_32.lib         =
//=---------------------------------------------------------------------------=
//=  Execute: rawServer                                                       =
//=---------------------------------------------------------------------------=
//=  Author: Ken Christensen                                                  =
//=          University of South Florida                                      =
//=          WWW: http://www.csee.usf.edu/~christen                           =
//=          Email: christen@csee.usf.edu                                     =
//=---------------------------------------------------------------------------=
//=  History:  KJC (03/26/17) - Genesis (from udpServer.c and rawsend.c)      =
//=============================================================================
//----- Include files ---------------------------------------------------------
#include <stdio.h>          // Needed for printf()
#include <string.h>         // Needed for memcpy() and strcpy()
#include <stdlib.h>         // Needed for exit()
#include <windows.h>        // Needed for all Winsock stuff

//===== Main program ==========================================================
int main()
{
  WORD wVersionRequested = MAKEWORD(1,1);       // Stuff for WSA functions
  WSADATA wsaData;                              // Stuff for WSA functions
  int                  server_s;        // Server socket descriptor
  struct sockaddr_in   server_addr;     // Server Internet address
  struct sockaddr_in   client_addr;     // Client Internet address
  struct in_addr       client_ip_addr;  // Client IP address
  int                  addr_len;        // Internet address length
  unsigned char        out_buf[4096];   // Output buffer for data
  unsigned char        in_buf[4096];    // Input buffer for data
  int                  retcode;         // Return code
  int                  i;               // Loop index

  // This stuff initializes winsock
  WSAStartup(wVersionRequested, &wsaData);

  // Create a raw socket
  server_s = socket(AF_INET, SOCK_RAW, IPPROTO_RAW);
  if (server_s < 0)
  {
    printf("*** ERROR - socket() failed \n");
    exit(-1);
  }

  // Fill-in my socket's address information
  server_addr.sin_family = AF_INET;                 // Address family to use
  server_addr.sin_addr.s_addr = htonl(INADDR_ANY);  // Listen on any IP address
  retcode = bind(server_s, (struct sockaddr *)&server_addr,
    sizeof(server_addr));
  if (retcode < 0)
  {
    printf("*** ERROR - bind() failed \n");
    exit(-1);
  }

  // Wait to receive a message from client
  printf("Waiting for recvfrom() to complete... \n");
  addr_len = sizeof(client_addr);
  retcode = recvfrom(server_s, in_buf, sizeof(in_buf), 0,
    (struct sockaddr *)&client_addr, &addr_len);
  if (retcode < 0)
  {
    printf("*** ERROR - recvfrom() failed \n");
    exit(-1);
  }

  // Copy the four-byte client IP address into an IP address structure
  memcpy(&client_ip_addr, &client_addr.sin_addr.s_addr, 4);

  // Print an informational message of IP address of the client
  printf("IP address of client = %s \n", inet_ntoa(client_ip_addr));

  // Output the received message (IP header and then payload)
  printf("Received from client: ");
  for (i=0; i<20; i++)
    printf("%02x", in_buf[i]);
  printf(" | ");
  for(i=20; i<retcode; i++)
    printf("%c", in_buf[i]);
  printf("\n");

  // Send to the client using the server socket
  strcpy(out_buf, "This is a reply message from SERVER to CLIENT");
  retcode = sendto(server_s, out_buf, (strlen(out_buf) + 1), 0,
    (struct sockaddr *)&client_addr, sizeof(client_addr));
  if (retcode < 0)
  {
    printf("*** ERROR - sendto() failed \n");
    exit(-1);
  }

  // Close all open sockets
  retcode = closesocket(server_s);
  if (retcode < 0)
  {
    printf("*** ERROR - closesocket() failed \n");
    exit(-1);
  }

  // This stuff cleans-up winsock
  WSACleanup();

  // Return zero and terminate
  return(0);
}