# -*- Mode: Python; tab-width: 4 -*-

#	Author: Sam Rushing <rushing@nightmare.com>
#	Copyright 1996-2000 by Sam Rushing
#						 All Rights Reserved.
#

# An extensible, configurable, asynchronous FTP server.
# 
# All socket I/O is non-blocking, however file I/O is currently
# blocking.  Eventually file I/O may be made non-blocking, too, if it
# seems necessary.  Currently the only CPU-intensive operation is
# getting and formatting a directory listing.  [this could be moved
# into another process/directory server, or another thread?]
#
# Only a subset of RFC 959 is implemented, but much of that RFC is
# vestigial anyway.  I've attempted to include the most commonly-used
# commands, using the feature set of wu-ftpd as a guide.

import asyncore
import asynchat

import os
import regsub
import socket
import stat
import string
import sys
import time

# TODO: implement a directory listing cache.  On very-high-load
# servers this could save a lot of disk abuse, and possibly the
# work of computing emulated unix ls output.

# Potential security problem with the FTP protocol?  I don't think
# there's any verification of the origin of a data connection.  Not
# really a problem for the server (since it doesn't send the port
# command, except when in PASV mode) But I think a data connection
# could be spoofed by a program with access to a sniffer - it could
# watch for a PORT command to go over a command channel, and then
# connect to that port before the server does.

# Unix user id's:
# In order to support assuming the id of a particular user,
# it seems there are two options:
# 1) fork, and seteuid in the child
# 2) carefully control the effective uid around filesystem accessing
#    methods, using try/finally. [this seems to work]

VERSION = '1.1'

from counter import counter
import producers
import status_handler
import logger
import string

class ftp_channel (asynchat.async_chat):

	# defaults for a reliable __repr__
	addr = ('unknown','0')

	# unset this in a derived class in order
	# to enable the commands in 'self.write_commands'
	read_only = 1
	write_commands = ['appe','dele','mkd','rmd','rnfr','rnto','stor','stou']

	restart_position = 0

	# comply with (possibly troublesome) RFC959 requirements
	# This is necessary to correctly run an active data connection
	# through a firewall that triggers on the source port (expected
	# to be 'L-1', or 20 in the normal case).
	bind_local_minus_one = 0

	def __init__ (self, server, conn, addr):
		self.server = server
		self.current_mode = 'a'
		self.addr = addr
		asynchat.async_chat.__init__ (self, conn)
		self.set_terminator ('\r\n')

		# client data port.  Defaults to 'the same as the control connection'.
		self.client_addr = (addr[0], 21)

		self.client_dc = None
		self.in_buffer = ''
		self.closing = 0
		self.passive_acceptor = None
		self.passive_connection = None
		self.filesystem = None
		self.authorized = 0
		# send the greeting
		self.respond (
			'220 %s FTP server (Medusa Async V%s [experimental]) ready.' % (
				self.server.hostname,
				VERSION
				)
			)

#	def __del__ (self):
#		print 'ftp_channel.__del__()'

	# --------------------------------------------------
	# async-library methods
	# --------------------------------------------------

	def handle_expt (self):
		# this is handled below.  not sure what I could
		# do here to make that code less kludgish.
		pass

	def collect_incoming_data (self, data):
		self.in_buffer = self.in_buffer + data
		if len(self.in_buffer) > 4096:
			# silently truncate really long lines
			# (possible denial-of-service attack)
			self.in_buffer = ''

	def found_terminator (self):

		line = self.in_buffer

		if not len(line):
			return

		sp = string.find (line, ' ')
		if sp != -1:
			line = [line[:sp], line[sp+1:]]
		else:
			line = [line]

		command = string.lower (line[0])
		# watch especially for 'urgent' abort commands.
		if string.find (command, 'abor') != -1:
			# strip off telnet sync chars and the like...
			while command and command[0] not in string.letters:
				command = command[1:]
		fun_name = 'cmd_%s' % command
		if command != 'pass':
			self.log ('<== %s' % repr(self.in_buffer)[1:-1])
		else:
			self.log ('<== %s' % line[0]+' <password>')
		self.in_buffer = ''
		if not hasattr (self, fun_name):
			self.command_not_understood (line[0])
			return
		fun = getattr (self, fun_name)
		if (not self.authorized) and (command not in ('user', 'pass', 'help', 'quit')):
			self.respond ('530 Please log in with USER and PASS')
		elif (not self.check_command_authorization (command)):
			self.command_not_authorized (command)
		else:
			try:
				result = apply (fun, (line,))
			except:
				self.server.total_exceptions.increment()
				(file, fun, line), t,v, tbinfo = asyncore.compact_traceback()
				if self.client_dc:
					try:
						self.client_dc.close()
					except:
						pass
				self.respond (
					'451 Server Error: %s, %s: file: %s line: %s' % (
						t,v,file,line,
						)
					)

	closed = 0
	def close (self):
		if not self.closed:
			self.closed = 1
			if self.passive_acceptor:
				self.passive_acceptor.close()
			if self.client_dc:
				self.client_dc.close()
			self.server.closed_sessions.increment()
			asynchat.async_chat.close (self)

	# --------------------------------------------------
	# filesystem interface functions.
	# override these to provide access control or perform
	# other functions.
	# --------------------------------------------------

	def cwd (self, line):
		return self.filesystem.cwd (line[1])

	def cdup (self, line):
		return self.filesystem.cdup()

	def open (self, path, mode):
		return self.filesystem.open (path, mode)

	# returns a producer
	def listdir (self, path, long=0):
		return self.filesystem.listdir (path, long)

	def get_dir_list (self, line, long=0):
		# we need to scan the command line for arguments to '/bin/ls'...
		args = line[1:]
		path_args = []
		for arg in args:
			if arg[0] != '-':
				path_args.append (arg)
			else:
				# ignore arguments
				pass
		if len(path_args) < 1:
			dir = '.'
		else:
			dir = path_args[0]
		return self.listdir (dir, long)

	# --------------------------------------------------
	# authorization methods
	# --------------------------------------------------

	def check_command_authorization (self, command):
		if command in self.write_commands and self.read_only:
			return 0
		else:
			return 1

	# --------------------------------------------------
	# utility methods
	# --------------------------------------------------

	def log (self, message):
		self.server.logger.log (
			self.addr[0],
			'%d %s' % (
				self.addr[1], message
				)
			)

	def respond (self, resp):
		self.log ('==> %s' % resp)
		self.push (resp + '\r\n')

	def command_not_understood (self, command):
		self.respond ("500 '%s': command not understood." % command)

	def command_not_authorized (self, command):
		self.respond (
			"530 You are not authorized to perform the '%s' command" % (
				command
				)
			)

	def make_xmit_channel (self):
		# In PASV mode, the connection may or may _not_ have been made
		# yet.  [although in most cases it is... FTP Explorer being
		# the only exception I've yet seen].  This gets somewhat confusing
		# because things may happen in any order...
		pa = self.passive_acceptor
		if pa:
			if pa.ready:
				# a connection has already been made.
				conn, addr = self.passive_acceptor.ready
				cdc = xmit_channel (self, addr)
				cdc.set_socket (conn)
				cdc.connected = 1
				self.passive_acceptor.close()
				self.passive_acceptor = None				
			else:
				# we're still waiting for a connect to the PASV port.
				cdc = xmit_channel (self)
		else:
			# not in PASV mode.
			ip, port = self.client_addr
			cdc = xmit_channel (self, self.client_addr)
			cdc.create_socket (socket.AF_INET, socket.SOCK_STREAM)
			if self.bind_local_minus_one:
				cdc.bind (('', self.server.port - 1))
			try:
				cdc.connect ((ip, port))
			except socket.error, why:
				self.respond ("425 Can't build data connection")
		self.client_dc = cdc

	# pretty much the same as xmit, but only right on the verge of
	# being worth a merge.
	def make_recv_channel (self, fd):
		pa = self.passive_acceptor
		if pa:
			if pa.ready:
				# a connection has already been made.
				conn, addr = pa.ready
				cdc = recv_channel (self, addr, fd)
				cdc.set_socket (conn)
				cdc.connected = 1
				self.passive_acceptor.close()
				self.passive_acceptor = None				
			else:
				# we're still waiting for a connect to the PASV port.
				cdc = recv_channel (self, None, fd)
		else:
			# not in PASV mode.
			ip, port = self.client_addr
			cdc = recv_channel (self, self.client_addr, fd)
			cdc.create_socket (socket.AF_INET, socket.SOCK_STREAM)
			try:
				cdc.connect ((ip, port))
			except socket.error, why:
				self.respond ("425 Can't build data connection")
		self.client_dc = cdc

	type_map = {
		'a':'ASCII',
		'i':'Binary',
		'e':'EBCDIC',
		'l':'Binary'
		}

	type_mode_map = {
		'a':'t',
		'i':'b',
		'e':'b',
		'l':'b'
		}

	# --------------------------------------------------
	# command methods
	# --------------------------------------------------

	def cmd_type (self, line):
		'specify data transfer type'
		# ascii, ebcdic, image, local <byte size>
		t = string.lower (line[1])
		# no support for EBCDIC
		# if t not in ['a','e','i','l']:
		if t not in ['a','i','l']:
			self.command_not_understood (string.join (line))
		elif t == 'l' and (len(line) > 2 and line[2] != '8'):
			self.respond ('504 Byte size must be 8')
		else:
			self.current_mode = t
			self.respond ('200 Type set to %s.' % self.type_map[t])


	def cmd_quit (self, line):
		'terminate session'
		self.respond ('221 Goodbye.')
		self.close_when_done()

	def cmd_port (self, line):
		'specify data connection port'
		info = string.split (line[1], ',')
		ip = string.join (info[:4], '.')
		port = string.atoi(info[4])*256 + string.atoi(info[5])
		# how many data connections at a time?
		# I'm assuming one for now...
		# TODO: we should (optionally) verify that the
		# ip number belongs to the client.  [wu-ftpd does this?]
		self.client_addr = (ip, port)
		self.respond ('200 PORT command successful.')

	def new_passive_acceptor (self):
		# ensure that only one of these exists at a time.
		if self.passive_acceptor is not None:
			self.passive_acceptor.close()
			self.passive_acceptor = None
		self.passive_acceptor = passive_acceptor (self)
		return self.passive_acceptor

	def cmd_pasv (self, line):
		'prepare for server-to-server transfer'
		pc = self.new_passive_acceptor()
		port = pc.addr[1]
		ip_addr = pc.control_channel.getsockname()[0]
		self.respond (
			'227 Entering Passive Mode (%s,%d,%d)' % (
				string.join (string.split (ip_addr, '.'), ','),
				port/256,
				port%256
				)
			)
		self.client_dc = None

	def cmd_nlst (self, line):
		'give name list of files in directory'
		# ncftp adds the -FC argument for the user-visible 'nlist'
		# command.  We could try to emulate ls flags, but not just yet.
		if '-FC' in line:
			line.remove ('-FC')
		try:
			dir_list_producer = self.get_dir_list (line, 0)
		except os.error, why:
			self.respond ('550 Could not list directory: %s' % repr(why))
			return
		self.respond (
			'150 Opening %s mode data connection for file list' % (
				self.type_map[self.current_mode]
				)
			)
		self.make_xmit_channel()
		self.client_dc.push_with_producer (dir_list_producer)
		self.client_dc.close_when_done()

	def cmd_list (self, line):
		'give list files in a directory'
		try:
			dir_list_producer = self.get_dir_list (line, 1)
		except os.error, why:
			self.respond ('550 Could not list directory: %s' % repr(why))
			return
		self.respond (
			'150 Opening %s mode data connection for file list' % (
				self.type_map[self.current_mode]
				)
			)
		self.make_xmit_channel()
		self.client_dc.push_with_producer (dir_list_producer)
		self.client_dc.close_when_done()

	def cmd_cwd (self, line):
		'change working directory'
		if self.cwd (line):
			self.respond ('250 CWD command successful.')
		else:
			self.respond ('550 No such directory.')			

	def cmd_cdup (self, line):
		'change to parent of current working directory'
		if self.cdup(line):
			self.respond ('250 CDUP command successful.')
		else:
			self.respond ('550 No such directory.')
		
	def cmd_pwd (self, line):
		'print the current working directory'
		self.respond (
			'257 "%s" is the current directory.' % (
				self.filesystem.current_directory()
				)
			)

	# modification time
	# example output:
	# 213 19960301204320
	def cmd_mdtm (self, line):
		'show last modification time of file'
		filename = line[1]
		if not self.filesystem.isfile (filename):
			self.respond ('550 "%s" is not a file' % filename)
		else:
			mtime = time.gmtime(self.filesystem.stat(filename)[stat.ST_MTIME])
			self.respond (
				'213 %4d%02d%02d%02d%02d%02d' % (
					mtime[0],
					mtime[1],
					mtime[2],
					mtime[3],
					mtime[4],
					mtime[5]
					)
				)

	def cmd_noop (self, line):
		'do nothing'
		self.respond ('200 NOOP command successful.')

	def cmd_size (self, line):
		'return size of file'
		filename = line[1]
		if not self.filesystem.isfile (filename):
			self.respond ('550 "%s" is not a file' % filename)
		else:
			self.respond (
				'213 %d' % (self.filesystem.stat(filename)[stat.ST_SIZE])
				)

	def cmd_retr (self, line):
		'retrieve a file'
		if len(line) < 2:
			self.command_not_understood (string.join (line))
		else:
			file = line[1]
			if not self.filesystem.isfile (file):
				self.log_info ('checking %s' % file)
				self.respond ('550 No such file')
			else:
				try:
					# FIXME: for some reason, 'rt' isn't working on win95
					mode = 'r'+self.type_mode_map[self.current_mode]
					fd = self.open (file, mode)
				except IOError, why:
					self.respond ('553 could not open file for reading: %s' % (repr(why)))
					return
				self.respond (
					"150 Opening %s mode data connection for file '%s'" % (
						self.type_map[self.current_mode],
						file
						)
					)
				self.make_xmit_channel()

				if self.restart_position:
					# try to position the file as requested, but
					# give up silently on failure (the 'file object'
					# may not support seek())
					try:
						fd.seek (self.restart_position)
					except:
						pass
					self.restart_position = 0

				self.client_dc.push_with_producer (
					file_producer (self, self.client_dc, fd)
					)
				self.client_dc.close_when_done()

	def cmd_stor (self, line, mode='wb'):
		'store a file'
		if len (line) < 2:
			self.command_not_understood (string.join (line))
		else:
			if self.restart_position:
				restart_position = 0
				self.respond ('553 restart on STOR not yet supported')
				return
			file = line[1]
			# todo: handle that type flag
			try:
				fd = self.open (file, mode)
			except IOError, why:
				self.respond ('553 could not open file for writing: %s' % (repr(why)))
				return
			self.respond (
				'150 Opening %s connection for %s' % (
					self.type_map[self.current_mode],
					file
					)
				)
			self.make_recv_channel (fd)

	def cmd_abor (self, line):
		'abort operation'
		if self.client_dc:
			self.client_dc.close()
		self.respond ('226 ABOR command successful.')

	def cmd_appe (self, line):
		'append to a file'
		return self.cmd_stor (line, 'ab')

	def cmd_dele (self, line):
		if len (line) != 2:
			self.command_not_understood (string.join (line))
		else:
			file = line[1]
			if self.filesystem.isfile (file):
				try:
					self.filesystem.unlink (file)
					self.respond ('250 DELE command successful.')
				except:
					self.respond ('550 error deleting file.')
			else:
				self.respond ('550 %s: No such file.' % file)

	def cmd_mkd (self, line):
		if len (line) != 2:
			self.command.not_understood (string.join (line))
		else:
			path = line[1]
			try:
				self.filesystem.mkdir (path)
				self.respond ('257 MKD command successful.')
			except:
				self.respond ('550 error creating directory.')

	def cmd_rmd (self, line):
		if len (line) != 2:
			self.command.not_understood (string.join (line))
		else:
			path = line[1]
			try:
				self.filesystem.rmdir (path)
				self.respond ('250 RMD command successful.')
			except:
				self.respond ('550 error removing directory.')

	def cmd_user (self, line):
		'specify user name'
		if len(line) > 1:
			self.user = line[1]
			self.respond ('331 Password required.')
		else:
			self.command_not_understood (string.join (line))

	def cmd_pass (self, line):
		'specify password'
		if len(line) < 2:
			pw = ''
		else:
			pw = line[1]
		result, message, fs = self.server.authorizer.authorize (self, self.user, pw)
		if result:
			self.respond ('230 %s' % message)
			self.filesystem = fs
			self.authorized = 1
			self.log_info('Successful login: Filesystem=%s' % repr(fs))
		else:
			self.respond ('530 %s' % message)

	def cmd_rest (self, line):
		'restart incomplete transfer'
		try:
			pos = string.atoi (line[1])
		except ValueError:
			self.command_not_understood (string.join (line))
		self.restart_position = pos
		self.respond (
			'350 Restarting at %d. Send STORE or RETRIEVE to initiate transfer.' % pos
			)

	def cmd_stru (self, line):
		'obsolete - set file transfer structure'
		if line[1] in 'fF':
			# f == 'file'
			self.respond ('200 STRU F Ok')
		else:
			self.respond ('504 Unimplemented STRU type')

	def cmd_mode (self, line):
		'obsolete - set file transfer mode'
		if line[1] in 'sS':
			# f == 'file'
			self.respond ('200 MODE S Ok')
		else:
			self.respond ('502 Unimplemented MODE type')

# The stat command has two personalities.  Normally it returns status
# information about the current connection.  But if given an argument,
# it is equivalent to the LIST command, with the data sent over the
# control connection.  Strange.  But wuftpd, ftpd, and nt's ftp server
# all support it.
#
##	def cmd_stat (self, line):
##		'return status of server'
##		pass

	def cmd_syst (self, line):
		'show operating system type of server system'
		# Replying to this command is of questionable utility, because
		# this server does not behave in a predictable way w.r.t. the
		# output of the LIST command.  We emulate Unix ls output, but
		# on win32 the pathname can contain drive information at the front
		# Currently, the combination of ensuring that os.sep == '/'
		# and removing the leading slash when necessary seems to work.
		# [cd'ing to another drive also works]
		#
		# This is how wuftpd responds, and is probably
		# the most expected.  The main purpose of this reply is so that
		# the client knows to expect Unix ls-style LIST output.
		self.respond ('215 UNIX Type: L8')
		# one disadvantage to this is that some client programs
		# assume they can pass args to /bin/ls.
		# a few typical responses:
		# 215 UNIX Type: L8 (wuftpd)
		# 215 Windows_NT version 3.51
		# 215 VMS MultiNet V3.3
		# 500 'SYST': command not understood. (SVR4)

	def cmd_help (self, line):
		'give help information'
		# find all the methods that match 'cmd_xxxx',
		# use their docstrings for the help response.
		attrs = dir(self.__class__)
		help_lines = []
		for attr in attrs:
			if attr[:4] == 'cmd_':
				x = getattr (self, attr)
				if type(x) == type(self.cmd_help):
					if x.__doc__:
						help_lines.append ('\t%s\t%s' % (attr[4:], x.__doc__))
		if help_lines:
			self.push ('214-The following commands are recognized\r\n')
			self.push_with_producer (producers.lines_producer (help_lines))
			self.push ('214\r\n')
		else:
			self.push ('214-\r\n\tHelp Unavailable\r\n214\r\n')

class ftp_server (asyncore.dispatcher):
	# override this to spawn a different FTP channel class.
	ftp_channel_class = ftp_channel

	SERVER_IDENT = 'FTP Server (V%s)' % VERSION

	def __init__ (
		self,
		authorizer,
		hostname	=None,
		ip			='',
		port		=21,
		resolver	=None,
		logger_object=logger.file_logger (sys.stdout)
		):
		self.ip = ip
		self.port = port
		self.authorizer = authorizer

		if hostname is None:
			self.hostname = socket.gethostname()
		else:
			self.hostname = hostname

		# statistics
		self.total_sessions = counter()
		self.closed_sessions = counter()
		self.total_files_out = counter()
		self.total_files_in = counter()
		self.total_bytes_out = counter()
		self.total_bytes_in = counter()
		self.total_exceptions = counter()
		#
		asyncore.dispatcher.__init__ (self)
		self.create_socket (socket.AF_INET, socket.SOCK_STREAM)

		self.set_reuse_addr()
		self.bind ((self.ip, self.port))
		self.listen (5)

		if not logger_object:
			logger_object = sys.stdout

		if resolver:
			self.logger = logger.resolving_logger (resolver, logger_object)
		else:
			self.logger = logger.unresolving_logger (logger_object)

		self.log_info('FTP server started at %s\n\tAuthorizer:%s\n\tHostname: %s\n\tPort: %d' % (
			time.ctime(time.time()),
			repr (self.authorizer),
			self.hostname,
			self.port)
			)

	def writable (self):
		return 0

	def handle_read (self):
		pass

	def handle_connect (self):
		pass

	def handle_accept (self):
		conn, addr = self.accept()
		self.total_sessions.increment()
		self.log_info('Incoming connection from %s:%d' % (addr[0], addr[1]))
		self.ftp_channel_class (self, conn, addr)

	# return a producer describing the state of the server
	def status (self):

		def nice_bytes (n):
			return string.join (status_handler.english_bytes (n))

		return producers.lines_producer (
			['<h2>%s</h2>'				% self.SERVER_IDENT,
			 '<br>Listening on <b>Host:</b> %s' % self.hostname,
			 '<b>Port:</b> %d'			% self.port,
			 '<br>Sessions',
			 '<b>Total:</b> %s'			% self.total_sessions,
			 '<b>Current:</b> %d'		% (self.total_sessions.as_long() - self.closed_sessions.as_long()),
			 '<br>Files',
			 '<b>Sent:</b> %s'			% self.total_files_out,
			 '<b>Received:</b> %s'		% self.total_files_in,
			 '<br>Bytes',
			 '<b>Sent:</b> %s'			% nice_bytes (self.total_bytes_out.as_long()),
			 '<b>Received:</b> %s'		% nice_bytes (self.total_bytes_in.as_long()),
			 '<br>Exceptions: %s'		% self.total_exceptions,
			 ]
			)

# ======================================================================
#						 Data Channel Classes
# ======================================================================

# This socket accepts a data connection, used when the server has been
# placed in passive mode.  Although the RFC implies that we ought to
# be able to use the same acceptor over and over again, this presents
# a problem: how do we shut it off, so that we are accepting
# connections only when we expect them?  [we can't]
#
# wuftpd, and probably all the other servers, solve this by allowing
# only one connection to hit this acceptor.  They then close it.  Any
# subsequent data-connection command will then try for the default
# port on the client side [which is of course never there].  So the
# 'always-send-PORT/PASV' behavior seems required.
#
# Another note: wuftpd will also be listening on the channel as soon
# as the PASV command is sent.  It does not wait for a data command
# first.

# --- we need to queue up a particular behavior:
#  1) xmit : queue up producer[s]
#  2) recv : the file object
#
# It would be nice if we could make both channels the same.  Hmmm..
#

class passive_acceptor (asyncore.dispatcher):
	ready = None

	def __init__ (self, control_channel):
		# connect_fun (conn, addr)
		asyncore.dispatcher.__init__ (self)
		self.control_channel = control_channel
		self.create_socket (socket.AF_INET, socket.SOCK_STREAM)
		# bind to an address on the interface that the
		# control connection is coming from.
		self.bind ((
			self.control_channel.getsockname()[0],
			0
			))
		self.addr = self.getsockname()
		self.listen (1)

#	def __del__ (self):
#		print 'passive_acceptor.__del__()'

	def log (self, *ignore):
		pass

	def handle_accept (self):
		conn, addr = self.accept()
		dc = self.control_channel.client_dc
		if dc is not None:
			dc.set_socket (conn)
			dc.addr = addr
			dc.connected = 1
			self.control_channel.passive_acceptor = None
		else:
			self.ready = conn, addr
		self.close()


class xmit_channel (asynchat.async_chat):

	# for an ethernet, you want this to be fairly large, in fact, it
	# _must_ be large for performance comparable to an ftpd.  [64k] we
	# ought to investigate automatically-sized buffers...

	ac_out_buffer_size = 16384
	bytes_out = 0

	def __init__ (self, channel, client_addr=None):
		self.channel = channel
		self.client_addr = client_addr
		asynchat.async_chat.__init__ (self)
		
#	def __del__ (self):
#		print 'xmit_channel.__del__()'

	def log (*args):
		pass

	def readable (self):
		return not self.connected

	def writable (self):
		return 1

	def send (self, data):
		result = asynchat.async_chat.send (self, data)
		self.bytes_out = self.bytes_out + result
		return result

	def handle_error (self):
		# usually this is to catch an unexpected disconnect.
		self.log_info ('unexpected disconnect on data xmit channel', 'error')
		try:
			self.close()
		except:
			pass

	# TODO: there's a better way to do this.  we need to be able to
	# put 'events' in the producer fifo.  to do this cleanly we need
	# to reposition the 'producer' fifo as an 'event' fifo.

	def close (self):
		c = self.channel
		s = c.server
		c.client_dc = None
		s.total_files_out.increment()
		s.total_bytes_out.increment (self.bytes_out)
		if not len(self.producer_fifo):
			c.respond ('226 Transfer complete')
		elif not c.closed:
			c.respond ('426 Connection closed; transfer aborted')
		del c
		del s
		del self.channel
		asynchat.async_chat.close (self)

class recv_channel (asyncore.dispatcher):
	def __init__ (self, channel, client_addr, fd):
		self.channel = channel
		self.client_addr = client_addr
		self.fd = fd
		asyncore.dispatcher.__init__ (self)
		self.bytes_in = counter()

	def log (self, *ignore):
		pass

	def handle_connect (self):
		pass

	def writable (self):
		return 0

	def recv (*args):
		result = apply (asyncore.dispatcher.recv, args)
		self = args[0]
		self.bytes_in.increment(len(result))
		return result

	buffer_size = 8192

	def handle_read (self):
		block = self.recv (self.buffer_size)
		if block:
			try:
				self.fd.write (block)
			except IOError:
				self.log_info ('got exception writing block...', 'error')

	def handle_close (self):
		s = self.channel.server
		s.total_files_in.increment()
		s.total_bytes_in.increment(self.bytes_in.as_long())
		self.fd.close()
		self.channel.respond ('226 Transfer complete.')
		self.close()

import filesys

# not much of a doorman! 8^)
class dummy_authorizer:
	def __init__ (self, root='/'):
		self.root = root
	def authorize (self, channel, username, password):
		channel.persona = -1, -1
		channel.read_only = 1
		return 1, 'Ok.', filesys.os_filesystem (self.root)

class anon_authorizer:
	def __init__ (self, root='/'):
		self.root = root
		
	def authorize (self, channel, username, password):
		if username in ('ftp', 'anonymous'):
			channel.persona = -1, -1
			channel.read_only = 1
			return 1, 'Ok.', filesys.os_filesystem (self.root)
		else:
			return 0, 'Password invalid.', None

# ===========================================================================
# Unix-specific improvements
# ===========================================================================

if os.name == 'posix':

	class unix_authorizer:
		# return a trio of (success, reply_string, filesystem)
		def authorize (self, channel, username, password):
			import crypt
			import pwd
			try:
				info = pwd.getpwnam (username)
			except KeyError:
				return 0, 'No such user.', None
			mangled = info[1]
			if crypt.crypt (password, mangled[:2]) == mangled:
				channel.read_only = 0
				fs = filesys.schizophrenic_unix_filesystem (
					'/',
					info[5],
					persona = (info[2], info[3])
					)
				return 1, 'Login successful.', fs
			else:
				return 0, 'Password invalid.', None

		def __repr__ (self):
			return '<standard unix authorizer>'

	# simple anonymous ftp support
	class unix_authorizer_with_anonymous (unix_authorizer):
		def __init__ (self, root=None, real_users=0):
			self.root = root
			self.real_users = real_users

		def authorize (self, channel, username, password):
			if string.lower(username) in ['anonymous', 'ftp']:
				import pwd
				try:
					# ok, here we run into lots of confusion.
					# on some os', anon runs under user 'nobody',
					# on others as 'ftp'.  ownership is also critical.
					# need to investigate.
					# linux: new linuxen seem to have nobody's UID=-1,
					#    which is an illegal value.  Use ftp.
					ftp_user_info = pwd.getpwnam ('ftp')
					if string.lower(os.uname()[0]) == 'linux':
						nobody_user_info = pwd.getpwnam ('ftp')
					else:
						nobody_user_info = pwd.getpwnam ('nobody')
					channel.read_only = 1
					if self.root is None:
						self.root = ftp_user_info[5]
					fs = filesys.unix_filesystem (self.root, '/')
					return 1, 'Anonymous Login Successful', fs
				except KeyError:
					return 0, 'Anonymous account not set up', None
			elif self.real_users:
				return unix_authorizer.authorize (
					self,
					channel,
					username,
					password
					)
			else:
				return 0, 'User logins not allowed', None

class file_producer:
	block_size = 16384
	def __init__ (self, server, dc, fd):
		self.fd = fd
		self.done = 0
		
	def more (self):
		if self.done:
			return ''
		else:
			block = self.fd.read (self.block_size)
			if not block:
				self.fd.close()
				self.done = 1
			return block

# usage: ftp_server /PATH/TO/FTP/ROOT PORT
# for example:
# $ ftp_server /home/users/ftp 8021

if os.name == 'posix':
	def test (port='8021'):
		import sys
		fs = ftp_server (
			unix_authorizer(),
			port=string.atoi (port)
			)
		try:
			asyncore.loop()
		except KeyboardInterrupt:
			self.log_info('FTP server shutting down. (received SIGINT)', 'warning')
			# close everything down on SIGINT.
			# of course this should be a cleaner shutdown.
			asyncore.close_all()

	if __name__ == '__main__':
		test (sys.argv[1])
# not unix
else:
	def test ():
		fs = ftp_server (dummy_authorizer())
	if __name__ == '__main__':
		test ()

# this is the command list from the wuftpd man page
# '*' means we've implemented it.
# '!' requires write access
#
command_documentation = {
	'abor':	'abort previous command',							#*
	'acct':	'specify account (ignored)',
	'allo':	'allocate storage (vacuously)',
	'appe':	'append to a file',									#*!
	'cdup':	'change to parent of current working directory',	#*
	'cwd':	'change working directory',							#*
	'dele':	'delete a file',									#!
	'help':	'give help information',							#*
	'list':	'give list files in a directory',					#*
	'mkd':	'make a directory',									#!
	'mdtm':	'show last modification time of file',				#*
	'mode':	'specify data transfer mode',
	'nlst':	'give name list of files in directory',				#*
	'noop':	'do nothing',										#*
	'pass':	'specify password',									#*
	'pasv':	'prepare for server-to-server transfer',			#*
	'port':	'specify data connection port',						#*
	'pwd':	'print the current working directory',				#*
	'quit':	'terminate session',								#*
	'rest':	'restart incomplete transfer',						#*
	'retr':	'retrieve a file',									#*
	'rmd':	'remove a directory',								#!
	'rnfr':	'specify rename-from file name',					#!
	'rnto':	'specify rename-to file name',						#!
	'site':	'non-standard commands (see next section)',
	'size':	'return size of file',								#*
	'stat':	'return status of server',							#*
	'stor':	'store a file',										#*!
	'stou':	'store a file with a unique name',					#!
	'stru':	'specify data transfer structure',
	'syst':	'show operating system type of server system',		#*
	'type':	'specify data transfer type',						#*
	'user':	'specify user name',								#*
	'xcup':	'change to parent of current working directory (deprecated)',
	'xcwd':	'change working directory (deprecated)',
	'xmkd':	'make a directory (deprecated)',					#!
	'xpwd':	'print the current working directory (deprecated)',
	'xrmd':	'remove a directory (deprecated)',					#!
}


# debugging aid (linux)
def get_vm_size ():
	return string.atoi (string.split(open ('/proc/self/stat').readline())[22])

def print_vm():
	print 'vm: %8dk' % (get_vm_size()/1024)
