#include "server.h"

int main (int argc, char ** argv)
{
	struct in_addr remote_addr,
				   local_addr;
	unsigned short remote_port,
				   local_port;
	int listen_fd;

	ParseArgs (argc, argv, &remote_addr, &remote_port, &local_addr, &local_port);

	Initialise ();

	// Create server socket before becoming a daemon so
	// there is still a chance to print an error message.
	listen_fd = CreateServerSocket (local_addr, local_port);
	if ( listen_fd < 0 )
		pbomb ("Unable to create server socket");

	//Daemonise ();

	MainLoop (listen_fd, remote_addr, remote_port); // never returns

	exit (EXIT_SUCCESS);
}

// ParseArgs()
// Parse the command line arguments to extract the remote
// and local adresses and port numbers, ra, rp, la & lp.
// Exit the program gracefully upon error.
void ParseArgs (int argc, char ** argv, struct in_addr * ra, unsigned short * rp, struct in_addr * la, unsigned short * lp)
{
	// argv[0] = program name
	// argv[1] = remote_addr
	// argv[2] = remote_port
	// argv[3] = local_addr (optional)
	// argv[4] = local_port (optional)

	char * p = strrchr (argv[0], '/');

	strncpy (g_program_name, (p == NULL) ? argv[0] : p + 1, sizeof (g_program_name) - 1);

	if ( (argc < 3) || (argc > 5) )
	{
		fprintf (stderr, "usage: %s remote_addr remote_port [local_addr] [local_port]\n", argv[0]);
		exit (EXIT_FAILURE);
	}

	if ( NameToAddr (argv[1], ra) )
		hbomb ("Unable to resolve \"%s\" to an ip address", argv[1]);

	if ( NameToPort (argv[2], rp, "tcp") )
		quit ("Unable to resolve \"%s\" to a port number", argv[2]);

	if ( argc < 4 )
		la->s_addr = htonl (INADDR_ANY);
	else
		if ( NameToAddr (argv[3], la) )
			hbomb ("Unable to resolve \"%s\" to an ip address", argv[3]);

	if ( argc < 5 )
		memcpy (lp, rp, sizeof (*lp));
	else
		if ( NameToPort (argv[4], lp, "tcp") )
			quit ("Unable to resolve \"%s\" to a port number", argv[4]);
}

// Initialise()
// Setup syslog, signal handlers, and other intialisation.
void Initialise (void)
{
	openlog (g_program_name, LOG_PID, LOG_USER);
	syslog (LOG_INFO, "%s started", g_program_name);

	chdir ("/"); // Change working directory to the root.

	umask (0); // Clear our file mode creation mask

	set_signal_handler (SIGCHLD, sig_child);

	signal (SIGPIPE, SIG_IGN);
}

// sig_child()
// Handles SIGCHLD from exiting child processes.
void sig_child (int signo)
{
	pid_t pid;

	(void) signo; // suppress compiler warning

	for ( ; ; )
	{
		write(1, "SIG\n", sizeof("SIG\n"));
		pid = waitpid (WAIT_ANY, NULL, WNOHANG);

		if ( pid > 0 )
			syslog (LOG_INFO, "Caught SIGCHLD from pid %d", pid);
		else
			break;
	}
	write(1, "SIG...\n", sizeof("SIG...\n"));

	if ( (pid < 0) && (errno != ECHILD) )
		syslog (LOG_ERR, "waitpid(): %m"), exit (EXIT_FAILURE);

	return;
}

// CreateServerSocket()
// Create a socket, bind it to the specified address
// and port, and set it to listen for client connections.
// Returns < 0 on failure to bind, bombs on error otherwise,
// returns the fd of the new socket on success.
int CreateServerSocket (struct in_addr addr, unsigned short port)
{
	int err,
		fd;
	const int on = 1;
	struct sockaddr_in sa;

	// Create a socket and get its descriptor.
	fd = socket (AF_INET, SOCK_STREAM, 0);
	if ( fd < 0 )
		syslog (LOG_ERR, "socket(): %m"), exit (EXIT_FAILURE);

	// Set SO_REUSEADDR socket option
	if ( setsockopt (fd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof (on)) < 0 )
		syslog (LOG_ERR, "setsockopt(fd%d, SO_REUSEADDR): %m", fd);

	// Load a sa structure with the specified address and port
	sa.sin_family = AF_INET;
	sa.sin_port = htons (port);
	sa.sin_addr = addr;
	memset (sa.sin_zero, 0, sizeof (sa.sin_zero));

	// Bind our socket to the address and port specified
	err = bind (fd, (struct sockaddr *) &sa, sizeof (sa));
	if ( err < 0 )
	{
		syslog (LOG_ERR, "bind(): %m");
		return err;
	}

	// Tell socket to listen and queue up to 5 incoming connections.
	if ( listen (fd, 5) < 0 )
		syslog (LOG_ERR, "listen(): %m"), exit (EXIT_FAILURE);

	return fd;
}

// Daemonise()
// Put the program in the background, set PPID=1, create a
// new session and process group, without a controlling tty.
void Daemonise (void)
{
	pid_t pid;

	// Close stdin, stdout & stderr
	// TODO:
	//		open /dev/null and dup the fd to stdin, stdout & stderr
	//		close(STDIN_FILENO);
	//		close(STDOUT_FILENO);
	//		close(STDERR_FILENO);

	syslog (LOG_INFO, "%s daemonising", g_program_name);

	// Fork the process to put it in the background.

	pid = fork ();
	if ( pid == -1 )
		syslog (LOG_ERR, "fork(): %m"), exit (EXIT_FAILURE);

	// parent terminates here, so shell thinks the command is done.
	if ( pid )
		exit (0);

	syslog (LOG_INFO, "%s in background", g_program_name);

	// 1st child continues to run in the background with PPID=1

	// Become leader of a new session and a new process group,
	// with no controlling tty.
	setsid ();

	// Fork again to guarantee the process will
	// not be able to aquire a controlling tty.

	// signal (SIGHUP, SIG_IGN);
	// required according to Stevens' UNP2 p333

	pid = fork ();
	if (pid == -1)
		syslog (LOG_ERR, "fork(): %m"), exit (EXIT_FAILURE);

	if ( pid ) // 1st child terminates
		exit (0);

	// 2nd child continues, no longer a session or group leader

	syslog (LOG_INFO, "%s daemonised", g_program_name);
}

// MainLoop()
// Classic concurrent server model.
// Wait for a client to connect, fork a child process
// to do the business with the client, parent process
// continues to wait for the next connection.
// This function does not return.
void MainLoop (int listen_fd, struct in_addr rem_addr, unsigned short rem_port)
{
	int server_fd,
		client_fd;
	pid_t child_pid;

	for ( ; ; )
	{
		client_fd = AcceptClientConnection (listen_fd);

		child_pid = fork ();
		if ( child_pid == -1 )
			syslog (LOG_ERR, "fork(): %m"), exit (EXIT_FAILURE);

		if ( child_pid ) // parent
		{
			close (client_fd);

			syslog (LOG_INFO, "Forked child pid %d to deal with client", child_pid);

			continue;
		}
		else // child
		{
			close (listen_fd);

			server_fd = ConnectToServer (rem_addr, rem_port);

			Proxy (server_fd, client_fd);

			syslog (LOG_INFO, "exiting");
			_exit (0);
		}
	}
}

// Proxy()
// Copies data between server_fd and client_fd in both directions
// until one or other peer closes their connection.
void Proxy (int server_fd, int client_fd)
{
	pid_t helper_pid;

	syslog (LOG_INFO, "Proxy(fd%d, fd%d)", server_fd, client_fd);

	signal (SIGCHLD, SIG_IGN);

	helper_pid = fork ();
	if ( helper_pid == -1 )
		syslog (LOG_ERR, "fork(): %m"), exit (EXIT_FAILURE);

	if ( helper_pid ) // parent
	{
		syslog (LOG_INFO, "Forked child pid %d to help with proxying", helper_pid);

		Cat (server_fd, client_fd);

		shutdown (client_fd, 1);
		close (server_fd);
		close (client_fd);

		wait (0); // wait for helper to exit
	}
	else // child (helper)
	{
		Cat (client_fd, server_fd);

		shutdown (server_fd, 1);

		syslog (LOG_INFO, "exiting");
		exit (0); // helper exits here
	}
}

// AcceptClientConnection()
// waits for a tcp connect to the socket listen_fd, which
// must already be bound and set to listen on a local port.
// Bombs on error, returns the fd of the new socket on success.
int AcceptClientConnection (int listen_fd)
{
	int newfd;
	struct sockaddr_in sa;
	socklen_t socklen;

	syslog (LOG_INFO, "AcceptClientConnection(fd%d)", listen_fd);

	// Accept the connection and create a new socket for it.
	socklen = sizeof (sa);
	memset (&sa, 0, socklen);
	do
	{
		newfd = accept (listen_fd, (struct sockaddr *) &sa, &socklen);
	}
	while ( (newfd < 0) && (errno == EINTR) );

	syslog (LOG_INFO, "Accepted client connection on new socket fd%d", newfd);

	if ( newfd < 0 )
		syslog (LOG_ERR, "accept(): %m"), exit (EXIT_FAILURE);

	if ( socklen != sizeof (sa) )
		syslog (LOG_ERR, "accept() screwed up!"), exit (EXIT_FAILURE);

	return (newfd);
}

// ConnectToServer()
// attempts a tcp connect to the server specified
// by addr and port.  Bombs on failure to connect,
// returns the fd of the new socket on success.
int ConnectToServer (struct in_addr addr, unsigned short port)
{
	// TODO: have a timeout for connect() - see Unix socket FAQ 6.2

	int fd, err;
	struct sockaddr_in sa;

	// Create a socket and get its descriptor.
	fd = socket (AF_INET, SOCK_STREAM, 0);

	if ( fd < 0 )
		syslog (LOG_ERR, "socket(): %m"), exit (EXIT_FAILURE);

	sa.sin_family = AF_INET;
	sa.sin_port = htons (port);
	sa.sin_addr = addr;
	memset (sa.sin_zero, 0, sizeof (sa.sin_zero));

	err = connect (fd, (struct sockaddr *) &sa, sizeof (sa));
	if (err < 0)
	{
		syslog (LOG_ERR, "Unable to connect socket fd%d to server: %m", fd);
		exit (EXIT_FAILURE);
	}

	syslog (LOG_INFO, "Connected socket fd%d to server", fd);

	return fd;
}

// Cat()
// read data from in_fd and write it to out_fd until
// the connection is closed by one of the peers.
// Data is copied using a dynamically allocated buffer.
void Cat (int in_fd, int out_fd)
{
	unsigned char * const buf = (char *) malloc (sizeof(char) * BUF_SIZE);
	int bytes_rcvd,
		bytes_sent = (int) NULL,
		i;

	syslog (LOG_INFO, "Cat(fd%d, fd%d)", in_fd, out_fd);

	if ( buf == NULL )
		syslog (LOG_ERR, "malloc(): %m"), exit (EXIT_FAILURE);

	do
	{
		write(1, "DO\n", sizeof("DO\n"));
		bzero(buf, BUF_SIZE);
		bytes_rcvd = recv (in_fd, buf, BUF_SIZE, 0);

		for ( i = 0; i < bytes_rcvd; i += bytes_sent )
		{
			bytes_sent = send (out_fd, buf + i, bytes_rcvd - i, 0);

			if ( bytes_sent < 0 )
				break;
		}
		write(1, "WHILE\n", sizeof("WHILE\n"));
	}
	while ( (bytes_rcvd > 0) && (bytes_sent > 0) );
	
	write(1, "...\n", sizeof("...\n"));

	if ( (bytes_rcvd < 0) && (errno != ECONNRESET) )
		syslog (LOG_ERR, "recv(): %m"), exit (EXIT_FAILURE);

	if ( (bytes_sent < 0) && (errno != EPIPE) )
		syslog (LOG_ERR, "send(): %m"), exit (EXIT_FAILURE);

	free (buf);
}

// NameToAddress()
// Convert name to an ip address.
// Returns 0 on success, -1 on failure.
int NameToAddr (const char * name, struct in_addr * p_inaddr)
{
	struct hostent * he;

	// First, attempt to convert from string ip format
	// TODO: use inet_aton() instead
	p_inaddr->s_addr = inet_addr (name);
	if ( p_inaddr->s_addr != -1U ) // Success
		return 0;

	// Next, attempt to read from /etc/hosts or do a DNS lookup
	he = gethostbyname (name);
	if ( he != NULL ) // Success
	{
		memcpy (p_inaddr, he->h_addr, sizeof (struct in_addr));
		return 0;
	}

	return -1; // Failed to resolve name to an ip address
}

// NameToPort()
// Convert name to a port number. Name can either be a port name
// (in which case proto must also be set to either "tcp" or "udp")
// or name can be the ascii representation of the port number.
// Returns 0 on success, -1 on failure.
int NameToPort (const char * name, unsigned short * port, const char * proto)
{
	unsigned long lport;
	char * errpos;
	struct servent * se;

	// First, attempt to convert string to integer
	lport = strtoul (name, &errpos, 0);
	if ( (*errpos == 0) && (lport <= 65535) ) // Success
	{
		*port = lport;
		return 0;
	}

	// Next, attempt to read the string from /etc/services
	se = getservbyname (name, proto);
	if ( se != NULL) // Success
	{
		*port = ntohs (se->s_port);
		return 0;
	}

	return -1; // Failed to resolve port name to a number
}

// quit()
// Print an error message to stderr
// and syslog, then exit the program.
void quit (const char * fmt, ...) // quit with msg
{
	va_list ap;

	fflush (stdout);

	fprintf (stderr, "%s: ", g_program_name);

	va_start (ap, fmt);
	vfprintf (stderr, fmt, ap);
	va_end (ap);

	fputc ('\n', stderr);

	syslog (LOG_ERR, "I quit!");

	exit (EXIT_FAILURE);
}

// pbomb()
// Print an error message to stderr
// and syslog, then exit the program.
// pbomb() additionally include the
// string representation of errno.
void pbomb (const char * fmt, ...) // bomb with perror
{
	va_list ap;
	int errno_save = errno;
	char buf[100];

	fflush (stdout);

	fprintf (stderr, "%s: ", g_program_name);

	va_start (ap, fmt);
	vsnprintf (buf, sizeof (buf), fmt, ap);
	va_end (ap);

	errno = errno_save;
	perror (buf);

	syslog (LOG_ERR, "Bang!: %s: %m", buf);

	exit (EXIT_FAILURE);
}

// hbomb()
// Print an error message to stderr
// and syslog, then exit the program.
// hbomb() additionally include the
// string representation of h_errno.
void hbomb (const char * fmt, ...) // bomb with herror
{
	va_list ap;
	int h_errno_save = h_errno;
	char buf[100];

	fflush (stdout);

	fprintf (stderr, "%s: ", g_program_name);

	va_start (ap, fmt);
	vsnprintf (buf, sizeof (buf), fmt, ap);
	va_end (ap);

	h_errno = h_errno_save;
	herror (buf);

	syslog (LOG_ERR, "Bang!: %s: %s", buf, hstrerror (h_errno));

	exit (EXIT_FAILURE);
}

// set_signal_handler()
// Sets a signal handler function.
// Similar to signal() but this method
// is more portable between platforms.
void set_signal_handler (int signum, signal_handler_t sa_handler_func)
{
	struct sigaction act;

	act.sa_handler = sa_handler_func;
	sigemptyset (&(act.sa_mask));
	act.sa_flags = 0;

	if ( sigaction (signum, &act, NULL) < 0 )
	{
		syslog (LOG_ERR, "Error setting handler for signal %d: %m", signum);
		exit (EXIT_FAILURE);
	}
}