//-------------------------------------------------------------------
//	tcpserver4.cpp
//
//	This program revises the 'signal-handler' that we introduced 
//	into our 'tcpserver3.cpp' example, to avoid a race-condition
//	whereby some child-processes may become 'zombies' if client-
//	connections are broken too rapidly for the signal-handler to
//	properly 'wait' for each child to exit in turn individually.      
//	
//	       to compile:  $ g++ tcpserver4.cpp -o tcpserver4
//	       to execute:  $ ./tcpserver4
//
//	programmer: ALLAN CRUSE
//	written on: 10 MAR 2009
//-------------------------------------------------------------------

#include <stdio.h>	// for printf(), perror() 
#include <stdlib.h>	// for exit() 
#include <unistd.h>	// for read(), write(), close() 
#include <netinet/in.h>	// for socket(), bind(), listen(),  
#include <signal.h>	// for signal()
#include <wait.h>	// for wait()

#define DEMO_PORT	54321

void sigchld_action( int signo )
{
	while ( waitpid( -1, NULL, WNOHANG ) > 0 );
	
	signal( SIGCHLD, sigchld_action );	

	printf( "data was received, processed, and returned\n" );
	printf( "\nserver is listening on port %u \n", DEMO_PORT );
}



int main( int argc, char **argv )
{
	signal( SIGCHLD, sigchld_action );	

	//--------------------------------------------------
	// create a socket-address structure for our socket 
	//-------------------------------------------------- 
	struct sockaddr_in	haddr = { 0 };
	socklen_t		halen = sizeof( haddr );
	haddr.sin_family	= AF_INET;
	haddr.sin_port		= htons( DEMO_PORT );
	haddr.sin_addr.s_addr	= htonl( INADDR_ANY );

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

	//-----------------------------------------------------
	// bind this listening socket to our fixed port-number
	//----------------------------------------------------- 
	if ( bind( sock, (sockaddr*)&haddr, halen ) < 0 )
		{ perror( "bind" ); exit(1); }

	//-----------------------------------------------------
	// create a connection queue for this listening socket 
	//-----------------------------------------------------
	if ( listen( sock, 5 ) < 0 ) 
		{ perror( "listen" ); exit(1); }
	printf( "\nserver is listening on port %u \n", DEMO_PORT );

	//------------------------------------------------
	// enter the main look to process client requests
	//------------------------------------------------ 
	do	{
		//--------------------------------------------------
		// accept the next connection-request from a client
		//--------------------------------------------------
		struct sockaddr_in	paddr = { 0 };
		socklen_t		palen = sizeof( paddr );
		int	conn = accept( sock, (sockaddr*)&paddr, &palen );
		if ( conn < 0 ) { perror( "accept" ); exit(1); }

		//----------------------------------------------------
		// fork a child-process to handle this new connection
		//----------------------------------------------------
		int	pid = fork();
		if ( pid < 0 ) { perror( "fork" ); exit(1); }
		if ( pid > 0 )	
			{
			// parent closes the connection-socket
			close( conn );
			continue;
			}
		//-----------------------------------------------------
		// child can now receive characters sent by the client 
		//-----------------------------------------------------
		char	buf[ 3000 ] = {0};
		int	len = sizeof( buf );
		int	rx = 0;
		while ( rx < len )
			{
			int	inch = 0;
			int	i = read( conn, &inch, 1 );
			if ( i < 0 ) { perror( "read" ); exit(1); }
			if ( i == 0 ) break;
			buf[ rx ] = inch;
			++rx;
			}

		//-----------------------------------------------
		// convert all the received letters to uppercase		
		//-----------------------------------------------
		for (int i = 0; i < rx; i++)
			if (( buf[i] >= 'a' )&&( buf[i] <= 'z' )) 
				buf[i] += 'A' - 'a';

		//----------------------------------------------	
		// send the modified message back to the client
		//----------------------------------------------	
		int	tx = write( conn, buf, rx );
		if ( tx < 0 ) { perror( "write" ); exit(1); }

		//----------------------------------------------------
		// flush the output buffers and close this connection
		//----------------------------------------------------
		fflush( fdopen( conn, "rw" ) );
		close( conn );
		exit( 0 );
		}
	while( 1 );
}