//-------------------------------------------------------------------
//	peekdemo.cpp
//
//	This is a TCP client-application for use with our 'slowecho' 
//	server.  It transmits a message, then waits for that message
//	to be returned in its entirety, but uses the 'recv()' socket
//	function with the MSG_PEEK flag to watch characters arriving
//	one-by-one in the TCP socket's input-queue before it finally
//	dequeues them with 'read()' and shuts the socket connection.   
//	Our purpose here is to examine, in slow motion, the exchange 
//	of TCP packets using our 'nicwatch' packet-sniffing utility.  
//
//	     to compile:  $ g++ peekdemo.cpp -o peekdemo
//	     to execute:  $ ./peekdemo <hostname>
//
//	NOTE: For this demo a privileged user would need to turn off
//	the 'tcp_window_scaling' option so that outgoing TCP packets
//	will express the 'window-size' in bytes (without 'scaling').
//	For Linux kernel version 2.6.26, this can be done using: 
//
//	    root# echo 0 > /proc/sys/net/ipv4/tcp_window_scaling
//
//	programmer: ALLAN CRUSE
//	written on: 27 FEB 2009
//-------------------------------------------------------------------


#include <netdb.h>	// for gethostbyname(), socket()
#include <stdio.h>	// for printf(), perror() 
#include <stdlib.h>	// for exit() 
#include <unistd.h>	// for read(), write(), close() 
#include <string.h>	// for strncpy()


#define DEMO_PORT	54321


int main( int argc, char **argv )
{
	//-------------------------------------------------
	// get the server's hostname from the command-line
	//------------------------------------------------- 	
	if ( argc == 1 )
		{
		fprintf( stderr, "must specify server\n" );
		exit(1);
		}
	char	peername[ 64 ] = { 0 };
	strncpy( peername, argv[ 1 ], 63 );

	//--------------------------------------
	// obtain the IP-address for the server
	//-------------------------------------- 
	struct hostent	*pp = gethostbyname( peername );
	if ( !pp ) { herror( "gethostbyname" ); exit(1); }

	//--------------------------------------------
	// construct a socket-address for this server
	//-------------------------------------------- 
	struct sockaddr_in	paddr = { 0 };
	socklen_t		palen = sizeof( paddr );
	paddr.sin_family	= AF_INET;
	paddr.sin_port		= htons( DEMO_PORT );
	paddr.sin_addr.s_addr	= *(int32_t*)pp->h_addr;

	//---------------------------------------------------------------
	// prompt the user for the input-message and accept the response
	//--------------------------------------------------------------- 
	printf( "\nPlease type a short sentence on the line below: \n" );
	char	msg[ 80 ] = { 0 };
	int	n = read( STDIN_FILENO, msg, sizeof( msg ) );

	//---------------------------------------------------
	// create a socket for communication with the server
	//--------------------------------------------------- 
	int	sock = socket( AF_INET, SOCK_STREAM, IPPROTO_TCP );
	if ( sock < 0 ) { perror( "socket" ); exit(1); }

	//-------------------------------------------------
	// shrink the size of this socket's receive-buffer
	//------------------------------------------------- 
	int		oval = 256;
	socklen_t	olen = sizeof( oval );
	if ( setsockopt( sock, SOL_SOCKET, SO_RCVBUF, &oval, olen ) < 0 )
		{ perror( "setsockopt" ); exit(1); }

	//---------------------------------------------------
	// obtain the modified buffer-size for display later
	//---------------------------------------------------
	if ( getsockopt( sock, SOL_SOCKET, SO_RCVBUF, &oval, &olen ) < 0 )
		{ perror( "getsockopt" ); exit(1); }

	//----------------------------------------
	// establish a connection with the server 
	//---------------------------------------- 
	if ( connect( sock, (sockaddr*)&paddr, palen ) < 0 )
		{ perror( "connect" ); exit(1); }

	//-------------------------------------------------------
	// write the message-characters to the socket one-by-one
	//-------------------------------------------------------
	for (int i = 0; i < n; i++)
		if ( write( sock, msg+i, 1 ) < 0 )
			{ perror( "write" ); break; }
	
	//----------------------------------------------
	// shut down the writing end of this connection
	//----------------------------------------------- 	
	fflush( fdopen( sock, "rw" ) );
	if ( shutdown( sock, SHUT_WR ) < 0 ) perror( "shutdown" ); 

	//-----------------------------------------
	// receive all the replies from the server
	//----------------------------------------- 		
	char	buf[ 1500 ] = { 0 };
	int	len = sizeof( buf );

	int	m = 0;
	while( 1 ) 
		{
		int	px = recv( sock, buf, len, MSG_PEEK );
		if ( px < 0 ) { perror( "recv PEEK" ); exit(1); }
		if ( px == n ) break; 
		if ( px == m ) continue; 
		printf( "\r%s", buf );
		fflush( stdout );
		++m;
		}
	printf( "\n\nsize of socket's receive-buffer:" );
	printf( " 0x%04X (=%d bytes) \n\n", oval, oval );

	//--------------------------------------------------
	// close the socket and release its file descriptor 
	//--------------------------------------------------
	int	rx = read( sock, buf, len );
	if ( rx < 0 ) { perror( "read" ); exit(1); }
	if ( close( sock ) < 0 ) perror( "close" );
}