#include <sys\types.h>
#include <sys\socket.h>
#include <netinet\in.h>
#include <iostream.h>
#include <string.h>

void main(int argc, char *argv[])
{
  int s,       // our socket
      rc,      // return code
      c,       // client socket
      len;     // length of structure
  struct sockaddr_in server, client;

  s = socket(AF_INET, SOCK_STREAM, 0);  // create a socket
  if (s < 0){
    cerr << "Error! Cannot create socket." << endl;
    return;
    }

  len = sizeof(struct sockaddr_in);

  bzero(server, len);  // clear the data
  server.sin_family = AF_INET;
  server.sin_port = htons(7777);
  server.sin_addr = INADDR_ANY;
  rc = bind(s, (struct sockaddr *) &server, len);
  if (rc < 0) {
    cerr << "Error! Bind failed." << endl;
    return;
    }

  rc = listen(s, SOMAXCONN);  // change to passive socket
  if (rc < 0) {
    cerr << "Error! Listen failed." << endl;
    return;
    }

  for( ; ; ) {  // forever
    bzero(&client, len);
    c = accept(s, (struct sockaddr *)&client, &len);
    if (c < 0) {
      cerr << "Error! Accept failed." << endl;
      return;
      }

    // do some work with new socket c to client
    TalkToClient(c);
    }
}

// ----------------------------------------------------------------

void TalkToClient(int iSocket)
{
  int iRc,
      bNotDone;
  char szBuf[256],
       szOk[] = "OK",
       szErr[] = "ERR";
  bNotDone = TRUE;

  while (bNotDone == TRUE) {
    iRc = RecvLine(iSocket, szBuf, 256);
    if (iRc < 0) {
      cerr << "Error! RecvLine failed." << endl;
      bNotDone = FALSE;
      }
    if (strcmp(szBuf, "HELLO") == 0) {
      iRc = send(iSocket, szOk, strlen(szOk), 0);
      if (iRc < 0) {
        cerr << "Error! Send failed." << endl;
        bNotDone = FALSE
        }
      }
    else if (strcmp(szBuf, "GOODBYE") == 0) {
      iRc = send(iSocket, szOk, strlen(szOk), 0);
      if (iRc < 0) {
        cerr << "Error! Send failed." << endl;
        bNotDone = FALSE
        }
      bNotDone = FALSE;  // close connection on GOODBYE
      }
    else { // unknown message
      send(iSocket, szErr, strlen(szErr), 0);
      bNotDone = FALSE;
      }
    }

    close(iSocket);
}

// ----------------------------------------------------------------
// Receive a command line terminated by a telnet eol sequence

int RecvLine(int iSocket, char *szBuf, int iLen)
{
  int iBytesRead,
      iIdx,
      bNotDone;

  iBytesRead = recv(iSocket, &szBuf[0], 1, 0);
  iIdx = 1;
  bNotDone = TRUE;

  while (bNotDone == TRUE) {
    iBytesRead = recv(iSocket, &szBuf[iIdx], 1, 0);
    if (iBytesRead < 0) {
      return ( -1 );  // error receiving
      }

    iIdx++;
    if ( (szBuf[iIdx - 2] == '\r') &&
         (szBuf[iIdx – 1] == '\n')  ) {
      bNotDone = FALSE;  // got telnet eol
      }
    if (iIdx == iLen) {
      return ( -1 ); // error, buffer too small
      }
    }

   szBuf[iIdx - 2] = NULL;  // append null termination
   return ( TRUE );
}