#!/usr/bin/perl
##########################################################################
# Tentacle Server
# See http://www.openideas.info/wiki for protocol description.
# Tentacle have IANA assigned port tpc/41121 as official port.
##########################################################################
# Copyright (c) 2005-2009 Artica Soluciones Tecnologicas S.L
#
# This program is free software; you can redistribute it and/or
# modify it under the terms of the GNU General Public License
# as published by the Free Software Foundation; version 2
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
##########################################################################

package tentacle::server;

use strict;
use warnings;
use Getopt::Std;
use IO::Select;
use IO::Socket::INET;
use Thread::Semaphore;
use POSIX ":sys_wait_h";

# Program version
our $VERSION = '0.2.1';

# Address to listen on
my $t_address = '0.0.0.0';

# Block size for socket read/write operations in bytes
my $t_block_size = 1024;

# Client socket
my $t_client_socket;

# Run as daemon, 1 true, 0 false
my $t_daemon = 0;

# Storage directory
my $t_directory = '';

# Filters
my %t_filters;

# String containing quoted invalid file name characters
my $t_invalid_chars = '\?\[\]\/\\\=\+\<\>\:\;\'\,\*\~';

# Log messages, 1 enabled, 0 disabled
my $t_log = 0;

# Maximum number of simultaneous connections
my $t_max_conn = 10;

# Maximum file size allowed by the server in bytes
my $t_max_size = 2000000;

# File overwrite, 1 enabled, 0 disabled
my $t_overwrite = 0;

# Port to listen on
my $t_port = 41121;

# Server password
my $t_pwd = '';

# Do not output error messages, 1 enabled, 0 disabled
my $t_quiet = 0;

# Number of retries for socket read/write operations
my $t_retries = 3;

# Select handler
my $t_select;

# Semaphore
my $t_sem;

# Server socket
my $t_server_socket;

# Use SSL, 1 true, 0 false
my $t_ssl = 0;

# SSL ca certificate file
my $t_ssl_ca = '';

# SSL certificate file
my $t_ssl_cert = '';

# SSL private key file
my $t_ssl_key = '';

# SSL private key password
my $t_ssl_pwd = '';

# Timeout for socket read/write operations in seconds
my $t_timeout = 1;

################################################################################
## SUB print_help
## Print help screen.
################################################################################
sub print_help {

	print ("Usage: $0 -s <storage directory> [options]\n\n");
	print ("Tentacle server v$VERSION. See http://www.openideas.info/wiki for protocol description.\n\n");
	print ("Options:\n");
	print ("\t-a ip_address\tAddress to listen on (default $t_address).\n");
	print ("\t-c number\tMaximum number of simultaneous connections (default $t_max_conn).\n");
	print ("\t-d\t\tRun as daemon.\n");
	print ("\t-e cert\t\tOpenSSL certificate file. Enables SSL.\n");
	print ("\t-f ca_cert\tVerify that the peer certificate is signed by a ca.\n");
	print ("\t-h\t\tShow help.\n");
	print ("\t-i\t\tFilters.\n");
	print ("\t-k key\t\tOpenSSL private key file.\n");
	print ("\t-m size\t\tMaximum file size in bytes (default ${t_max_size}b).\n");
	print ("\t-o\t\tEnable file overwrite.\n");
	print ("\t-p port\t\tPort to listen on (default $t_port).\n");
	print ("\t-q\t\tQuiet. Do now print error messages.\n");
	print ("\t-r number\tNumber of retries for network opertions (default $t_retries).\n");
	print ("\t-t time\t\tTime-out for network operations in seconds (default ${t_timeout}s).\n");
	print ("\t-v\t\tBe verbose.\n");
	print ("\t-w\t\tPrompt for OpenSSL private key password.\n");
	print ("\t-x pwd\t\tServer password.\n\n");
}

################################################################################
## SUB daemonize
## Turn the current process into a daemon.
################################################################################
sub daemonize {
	my $pid;

	require POSIX;

	chdir ('/') || error ("Cannot chdir to /: $!.");
	umask 0;

	open (STDIN, '/dev/null') || error ("Cannot read /dev/null: $!.");

	# Do not be verbose when running as a daemon
	open (STDOUT, '>/dev/null') || error ("Cannot write to /dev/null: $!.");
	open (STDERR, '>/dev/null') || error ("Cannot write to /dev/null: $!.");

	# Fork
	$pid = fork ();
	if (! defined ($pid)) {
		error ("Cannot fork: $!.");
	}

	# Parent
	if ($pid != 0) {
		exit;
	}

	# Child
	POSIX::setsid () || error ("Cannot start a new session: $!.");
}

################################################################################
## SUB start_win_service
## Turn the current process into a Windows service.
################################################################################
#sub start_win_service {
#	require Win32::Daemon;
#
#	# Tell the OS to start the service
#	Win32::Daemon::StartService ();
#
#	# Wait until the service manager is ready
#	while (SERVICE_START_PENDING != Win32::Daemon::State()) {
#		sleep (1);
#	}
#
#	# Tell the service manager we are running
#	Win32::Daemon::State (SERVICE_RUNNING);
#
#	# Call Win32::Daemon::StopService() when done
#}

################################################################################
## SUB parse_options
## Parse command line options and initialize global variables.
################################################################################
sub parse_options {
	my %opts;
	my $tmp;

	# Get options
	if (getopts ('a:c:de:f:hi:k:m:op:qr:s:t:vwx:', \%opts) == 0 || defined ($opts{'h'})) {
		print_help ();
		exit 1;
	}

	# Address
	if (defined ($opts{'a'})) {
		$t_address = $opts{'a'};
		if ($t_address !~ /^[a-zA-Z\.]+$/ && ($t_address  !~ /^(\d+)\.(\d+)\.(\d+)\.(\d+)$/
			|| $1 < 0 || $1 > 255 || $2 < 0 || $2 > 255
			|| $3 < 0 || $3 > 255 || $4 < 0 || $4 > 255)) {
			error ("Address $t_address is not valid.");
		}
	}
	
	# Maximum simultaneous connections
	if (defined ($opts{'c'})) {
		$t_max_conn = $opts{'c'};
		if ($t_max_conn !~ /^\d+$/ || $t_max_conn < 1) {
			error ("Invalid number of maximum simultaneous connections.");
		}
	}

	# Run as daemon
	if (defined ($opts{'d'})) {
		if ($^ eq 'MSWin32') {
			error ("-d flag not available for this OS.");
		}

		$t_daemon = 1;
	}

	# Enable SSL
	if (defined ($opts{'e'})) {

		require IO::Socket::SSL;

		$t_ssl_cert = $opts{'e'};
		if (! -f $t_ssl_cert) {
			error ("File $t_ssl_cert does not exist.");
		}

		$t_ssl = 1;
	}

	# Verify peer certificate
	if (defined ($opts{'f'})) {
		$t_ssl_ca = $opts{'f'};
		if (! -f $t_ssl_ca) {
			error ("File $t_ssl_ca does not exist.");
		}
	}

	# Filters (regexp:dir;regexp:dir...)
	if (defined ($opts{'i'})) {
		my @filters = split (';', $opts{'i'});
		foreach my $filter (@filters) {
			my ($regexp, $dir) = split (':', $filter);
			next unless defined ($regexp) && defined ($dir);

			# Remove any trailing /
			my $char = chop ($dir);
			$dir .= $char if ($char) ne '/';

			$t_filters{$regexp} = $dir;
		}
	}

	# SSL private key file
	if (defined ($opts{'k'})) {
		$t_ssl_key = $opts{'k'};
		if (! -f $t_ssl_key) {
			error ("File $t_ssl_key does not exist.");
		}
	}

	# Maximum file size
	if (defined ($opts{'m'})) {
		$t_max_size = $opts{'m'};
		if ($t_max_size !~ /^\d+$/ || $t_max_size < 1) {
			error ("Invalid maximum file size.");
		}
	}

	# File overwrite
	if (defined ($opts{'o'})) {
		$t_overwrite = 1;
	}

	# Port
	if (defined ($opts{'p'})) {
		$t_port = $opts{'p'};
		if ($t_port !~ /^\d+$/ || $t_port < 1 || $t_port > 65535) {
			error ("Port $t_port is not valid.");
		}
	}

	# Quiet mode
	if (defined ($opts{'q'})) {
		$t_quiet = 1;
	}

	# Retries
	if (defined ($opts{'r'})) {
		$t_retries = $opts{'r'};
		if ($t_retries !~ /^\d+$/ || $t_retries < 1) {
			error ("Invalid number of retries for network operations.");
		}
	}

	# Storage directory
	if (defined ($opts{'s'})) {

		$t_directory = $opts{'s'};
		
		# Check that directory exists
		if (! -d $t_directory) {
			error ("Directory $t_directory does not exist.");
		}

		# Check directory permissions
		if (! -w $t_directory) {
			error ("Cannot write to directory $t_directory.");
		}

		# Remove the trailing / if present
		$tmp = chop ($t_directory);
		if ($tmp ne '/') {
			$t_directory .= $tmp;
		}
	}
	else {
		print_help ();
		exit 1;
	}

	# Timeout
	if (defined ($opts{'t'})) {
		$t_timeout = $opts{'t'};
		if ($t_timeout !~ /^\d+$/ || $t_timeout < 1) {
			error ("Invalid timeout for network operations.");
		}
	}

	# Be verbose
	if (defined ($opts{'v'})) {
		$t_log = 1;
	}

	# SSL private key password
	if (defined ($opts{'w'})) {
		$t_ssl_pwd = ask_passwd ("Enter private key file password: ", "Enter private key file password again for confirmation: ");
	}

	# Server password
	if (defined ($opts{'x'})) {
		$t_pwd = $opts{'x'};
	}
}

################################################################################
## SUB sigchld_handler
## Handle child process termination.
################################################################################
sub sigchld_handler {

	while (waitpid(-1, &WNOHANG) > 0) {
		$t_sem->up ();
	}

	$SIG{CHLD} = \&sigchld_handler;
}

################################################################################
## SUB start_server
## Open the server socket.
################################################################################
sub start_server {

	$t_server_socket = IO::Socket::INET->new (
		Listen    => $t_max_conn,
		LocalAddr => $t_address,
		LocalPort => $t_port,
		Proto     => 'tcp',
		ReuseAddr     => 1,
	);

        if (! defined ($t_server_socket)) {
		error ("Cannot open socket for address $t_address on port $t_port: $!.");
	}

	print_log ("Server listening on $t_address port $t_port (press <ctr-c> to stop)");
}

################################################################################
## SUB stop_server
## Close the server socket.
################################################################################
sub stop_server {
	
	$t_server_socket->close ();
	print_log ("Server going down");
	
	exit 0;
}

################################################################################
## SUB start_ssl
## Convert the client socket to an IO::Socket::SSL socket.
################################################################################
sub start_ssl {
	my $err;

	if ($t_ssl_ca eq '') {
		IO::Socket::SSL->start_SSL (
			$t_client_socket,
			SSL_cert_file => $t_ssl_cert,
			SSL_key_file => $t_ssl_key,
			SSL_passwd_cb => sub {return $t_ssl_pwd},
			SSL_server => 1,
			# Verify peer
			SSL_verify_mode => 0x01,
		);
	}
	else {
		IO::Socket::SSL->start_SSL (
			$t_client_socket,
			SSL_ca_file => $t_ssl_ca,
			SSL_cert_file => $t_ssl_cert,
			SSL_key_file => $t_ssl_key,
			SSL_passwd_cb => sub {return $t_ssl_pwd},
			SSL_server => 1,
			# Fail verification if no peer certificate exists
			SSL_verify_mode => 0x03,
		);
	}

	$err = IO::Socket::SSL::errstr ();
	if ($err ne '') {
		error ($err);
	}

	print_log ("SSL started for " . $t_client_socket->sockhost ());
}

################################################################################
## SUB accept_connection
## Accept an incoming connection and fork.
################################################################################
sub accept_connection {
	my $pid;

	while (1) {

		# Accept connection
		$t_client_socket = $t_server_socket->accept ();

		if (! defined ($t_client_socket)) {

			# EINTR
			if ($! ne '') {
				next;
			}

			error ("accept: $!.");
		}

		last;
	}

	print_log ("Client connected from " . $t_client_socket->sockhost ());

	# Fork and serve the client
	$pid = fork ();
	if (! defined ($pid)) {
		error ("Cannot fork: $!.");
	}
	
	# Child
	if ($pid == 0) {

		# We do not need the server socket
		$t_server_socket->close ();
		
		# Add client socket to select queue
		$t_select = IO::Select->new ();
		$t_select->add ($t_client_socket);
		
		# Start SSL
		if ($t_ssl == 1) {
			start_ssl ();
		}

		# Authenticate client
		if ($t_pwd ne '') {
			auth_pwd ();
		}

		serve_connection ();

		$t_client_socket->close ();

		# Must exit now
		exit;
	}

	# Parent
	$t_client_socket->close ();
}

################################################################################
## SUB serve_connection
## Read and process commands from the client.
################################################################################
sub serve_connection {
	my $command;

	# Read commands
	while ($command = recv_command ($t_block_size)) {
		
		# Client wants to send a file
		if ($command =~ /^SEND <(.*)> SIZE (\d+)$/) {
			print_log ("Request to send file '$1' size ${2}b from " . $t_client_socket->sockhost ());
			recv_file ($1, $2);
		}
		# Client wants to receive a file
		elsif ($command =~ /^RECV <(.*)>$/) {
			print_log ("Request to receive file '$1' from " . $t_client_socket->sockhost ());
			send_file ($1);
		}
		# Quit
		elsif ($command =~ /^QUIT$/) {
			print_log ("Connection closed from " . $t_client_socket->sockhost ());
			last;
		}
		# Unknown command
		else {
			print_log ("Unknown command '$command' from " . $t_client_socket->sockhost ());
			last;
		}
	}
}

################################################################################
## SUB auth_pwd
## Authenticate client with server password.
################################################################################
sub auth_pwd {
	my $client_digest;
	my $command;
	my $pwd_digest;

	require Digest::MD5;
	
	# Wait for password
	$command = recv_command ($t_block_size);
	if ($command !~ /^PASS (.*)$/) {
		error ("Client " . $t_client_socket->sockhost () . " did not authenticate.");
	}
	
	$client_digest = $1;
	$pwd_digest = Digest::MD5::md5 ($t_pwd);
	$pwd_digest = Digest::MD5::md5_hex ($pwd_digest);

	if ($client_digest ne $pwd_digest) {
		error ("Invalid password from " . $t_client_socket->sockhost () . ".");
	}

	print_log ("Client " . $t_client_socket->sockhost () . " authenticated");
	send_data ("PASS OK\n");
}

################################################################################
## SUB recv_file
## Receive a file of size $_[1] and save it in $t_directory as $_[0].
################################################################################
sub recv_file {
	my $base_name = $_[0];
	my $data = '';
	my $file;
	my $size = $_[1];

	# Check file name
	if ($base_name =~ /[$t_invalid_chars]/) {
		print_log ("File '$base_name' size ${size}b from " . $t_client_socket->sockhost () . " has an invalid file name");
		send_data ("SEND ERR\n");
		return;
	}

	# Check file size, empty files are not allowed
	if ($size < 1 || $size > $t_max_size) {
		print_log ("File '$base_name' size ${size}b from " . $t_client_socket->sockhost () . " is too big");
		send_data ("SEND ERR\n");
		return;
	}
	
	# Apply filters
	$file = "$t_directory/" . apply_filters ($base_name) . $base_name;

	# Check if file exists
	if (-f $file && $t_overwrite == 0) {
		print_log ("File '$base_name' size ${size}b from " . $t_client_socket->sockhost () . " already exists");
		send_data ("SEND ERR\n");
		return;
	}

	send_data ("SEND OK\n");

	# Receive file
	$data = recv_data_block ($size);

	# Write it to disk
	open (FILE, "> $file") || error ("Cannot open file '$file' for writing.");
	binmode (FILE);
	print (FILE $data);
	close (FILE);

	send_data ("SEND OK\n");
	print_log ("Received file '$base_name' size ${size}b from " . $t_client_socket->sockhost ());
}

################################################################################
## SUB send_file
## Send a file to the client
################################################################################
sub send_file {
	my $base_name = $_[0];
	my $data = '';
	my $file;
	my $response;
	my $size;

	# Check file name
	if ($base_name =~ /[$t_invalid_chars]/) {
		print_log ("Requested file '$base_name' from " . $t_client_socket->sockhost () . " has an invalid file name");
		send_data ("RECV ERR\n");
		return;
	}
	
	# Apply filters
	$file = "$t_directory/" . apply_filters ($base_name) . $base_name;

	# Check if file exists
	if (! -f $file) {
		print_log ("Requested file '$file' from " . $t_client_socket->sockhost () . " does not exist");
		send_data ("RECV ERR\n");
		return;
	}

	$size = -s $file;
	send_data ("RECV SIZE $size\n");
	
	# Wait for client response
	$response = recv_command ($t_block_size);
	if ($response ne "RECV OK") {
		print_log ("Requested file '$file' from " . $t_client_socket->sockhost () . " not sent");
		return;
	}

	# Send the file
	open (FILE, $file) || error ("Cannot open file '$file' for reading.");
	binmode (FILE);

	while ($data = <FILE>) {
		send_data ($data);
	}

	close (FILE);

	print_log ("Requested file '$file' from " . $t_client_socket->sockhost () . " sent");
}

################################################################################
# Common functions
################################################################################

################################################################################
## SUB print_log
## Print log messages.
################################################################################
sub print_log {

	if ($t_log == 1) {
		print (STDOUT "[log] $_[0]\n");
	}
}

################################################################################
## SUB error
## Print an error and exit the program.
################################################################################
sub error {

	if ($t_quiet == 0) {
		print (STDERR "[err] $_[0]\n");
	}

	exit 1;
}

################################################################################
## SUB recv_data
## Read data from the client socket. Returns the number of bytes read and the
## string of bytes as a two element array.
################################################################################
sub recv_data {
	my $data;
	my $read;
	my $retries = 0;
	my $size = $_[0];

	while (1) {

		# Try to read data from the socket
		if ($t_select->can_read ($t_timeout)) {
			
			# Read at most $size bytes
			$read = sysread ($t_client_socket, $data, $size);

			# Read error
			if (! defined ($read)) {
				error ("Read error from " . $t_client_socket->sockhost () . ": $!.");
			}
	
			# EOF
			if ($read == 0) {
				error ("Connection from " . $t_client_socket->sockhost () . " unexpectedly closed.");
			}
	
			return ($read, $data);
		}

		# Retry
		$retries++;

		# But check for error conditions first
		if ($retries > $t_retries) {
			error ("Connection from " . $t_client_socket->sockhost () . " timed out.");
		}
	}
}

################################################################################
## SUB send_data
## Write data to the client socket.
################################################################################
sub send_data {
	my $data = $_[0];
	my $retries = 0;
	my $size;
	my $total = 0;
	my $written;

	$size = length ($data);

	while (1) {

		# Try to write data to the socket
		if ($t_select->can_write ($t_timeout)) {

			$written = syswrite ($t_client_socket, $data, $size - $total, $total);

			# Write error
			if (! defined ($written)) {
				error ("Connection error from " . $t_client_socket->sockhost () . ": $!.");
			}
			
			# EOF
			if ($written == 0) {
				error ("Connection from " . $t_client_socket->sockhost () . " unexpectedly closed.");
			}
	
		}

		$total += $written;

		# Check if all data was written
		if ($total == $size) {
			return;
		}

		# Retry
		$retries++;

		# But check for error conditions first
		if ($retries > $t_retries) {
			error ("Connection from " . $t_client_socket->sockhost () . " timed out.");
		}
	}
}

################################################################################
## SUB recv_command
## Read a command from the client, ended by a new line character.
################################################################################
sub recv_command {
	my $buffer;
	my $char;
	my $command = '';
	my $read;
	my $total = 0;

	while (1) {
		
		($read, $buffer) = recv_data ($t_block_size);
		$command .= $buffer;
		$total += $read;

		# Check if the command is complete
		$char = chop ($command);
		if ($char eq "\n") {
			return $command;
		}
	
		$command .= $char;

		# Avoid overflow
		if ($total > $t_block_size) {
			error ("Received too much data from " . $t_client_socket->sockhost () . ".");
		}
	}
}

################################################################################
## SUB recv_data_block
## Read $_[0] bytes of data from the client.
################################################################################
sub recv_data_block {
	my $buffer = '';
	my $data = '';
	my $read;
	my $size = $_[0];
	my $total = 0;

	while (1) {

		($read, $buffer) = recv_data ($size - $total);
		$data .= $buffer;
		$total += $read;

		# Check if all data has been read
		if ($total == $size) {
			return $data;
		}
	}
}

################################################################################
## SUB ask_passwd
## Asks the user for a password.
################################################################################
sub ask_passwd {
	my $msg1 = $_[0];
	my $msg2 = $_[1];
	my $pwd1;
	my $pwd2;

	require Term::ReadKey;

	# Disable keyboard echo
	Term::ReadKey::ReadMode('noecho');
	
	# Promt for password
	print ($msg1);
	$pwd1 = Term::ReadKey::ReadLine(0);
	print ("\n$msg2");
	$pwd2 = Term::ReadKey::ReadLine(0);
	print ("\n");

	# Restore original settings
	Term::ReadKey::ReadMode('restore');

	if ($pwd1 ne $pwd2) {
		print ("Error: passwords do not match.\n");
		exit 1;
	}

	# Remove the trailing new line character
	chop $pwd1;

	return $pwd1;
}

################################################################################
## SUB apply_filters
## Applies filters to the given file.
################################################################################
sub apply_filters ($) {
	my ($file_name) = @_;

	while (my ($regexp, $dir) = each (%t_filters)) {
		if ($file_name =~ /$regexp/) {
			print_log ("File '$file_name' matches filter '$regexp' (changing to directory '$dir')");
			return $dir . '/';
		}
	}

	return '';
}

################################################################################
# Main
################################################################################

# Never run as root
if ($> == 0 && $^O ne 'MSWin32') {
	print ("Error: for safety reasons $0 cannot be run with root privileges.\n");
	exit 1;
}

# Parse command line options
parse_options ();

# Check command line arguments
if ($#ARGV != -1) {
	print_help ();
	exit 1;
}

# Run as daemon?
if ($t_daemon == 1 && $^O ne 'MSWin32') {
	daemonize ();
}

# Handle ctr-c
if ($^O eq 'MSWin32') {
	$SIG{INT2} = \&stop_server;
}
else {
	$SIG{INT} = \&stop_server;
}

# Handle SIGCHLD
$SIG{CHLD} = \&sigchld_handler;

start_server ();

# Initialize semaphore
$t_sem = Thread::Semaphore->new ($t_max_conn);

# Accept connections
while (1) {
	$t_sem->down ();
	accept_connection ();
}