python
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+# -*- Mode: Python; tab-width: 4 -*-
+#	$Id$
+#	Author: Sam Rushing <[email protected]>
+
+# ======================================================================
+# Copyright 1996 by Sam Rushing
+# 
+#                         All Rights Reserved
+# 
+# Permission to use, copy, modify, and distribute this software and
+# its documentation for any purpose and without fee is hereby
+# granted, provided that the above copyright notice appear in all
+# copies and that both that copyright notice and this permission
+# notice appear in supporting documentation, and that the name of Sam
+# Rushing not be used in advertising or publicity pertaining to
+# distribution of the software without specific, written prior
+# permission.
+# 
+# SAM RUSHING DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
+# INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN
+# NO EVENT SHALL SAM RUSHING BE LIABLE FOR ANY SPECIAL, INDIRECT OR
+# CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS
+# OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT,
+# NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+# CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+# ======================================================================
+
+import socket
+import asyncore
+import string
+
+# This class adds support for 'chat' style protocols - where one side
+# sends a 'command', and the other sends a response (examples would be
+# the common internet protocols - smtp, nntp, ftp, etc..).
+
+# The handle_read() method looks at the input stream for the current
+# 'terminator' (usually '\r\n' for single-line responses, '\r\n.\r\n'
+# for multi-line output), calling self.found_terminator() on its
+# receipt.
+
+# for example:
+# Say you build an async nntp client using this class.  At the start
+# of the connection, you'll have self.terminator set to '\r\n', in
+# order to process the single-line greeting.  Just before issuing a
+# 'LIST' command you'll set it to '\r\n.\r\n'.  The output of the LIST
+# command will be accumulated (using your own 'collect_incoming_data'
+# method) up to the terminator, and then control will be returned to
+# you - by calling your self.found_terminator() method
+
+class async_chat (asyncore.dispatcher):
+	"""This is an abstract class.  You must derive from this class, and add
+	the two methods collect_incoming_data() and found_terminator()"""
+
+	# these are overridable defaults
+
+	ac_in_buffer_size	= 4096
+	ac_out_buffer_size	= 4096
+
+	def __init__ (self, conn=None):
+		self.ac_in_buffer = ''
+		self.ac_out_buffer = ''
+		self.producer_fifo = fifo()
+		asyncore.dispatcher.__init__ (self, conn)
+
+	def set_terminator (self, term):
+		"Set the input delimiter.  Can be a fixed string of any length, or None"
+		if term is None:
+			self.terminator = ''
+		else:
+			self.terminator = term
+
+	def get_terminator (self):
+		return self.terminator
+
+	# grab some more data from the socket,
+	# throw it to the collector method,
+	# check for the terminator,
+	# if found, transition to the next state.
+
+	def handle_read (self):
+
+		try:
+			data = self.recv (self.ac_in_buffer_size)
+		except socket.error, why:
+			import sys
+			self.handle_error (sys.exc_type, sys.exc_value, sys.exc_traceback)
+			return
+
+		self.ac_in_buffer = self.ac_in_buffer + data
+
+		# Continue to search for self.terminator in self.ac_in_buffer,
+		# while calling self.collect_incoming_data.  The while loop
+		# is necessary because we might read several data+terminator
+		# combos with a single recv(1024).
+
+		while self.ac_in_buffer:
+			terminator = self.get_terminator()
+			terminator_len = len(terminator)
+			# 4 cases:
+			# 1) end of buffer matches terminator exactly:
+			#    collect data, transition
+			# 2) end of buffer matches some prefix:
+			#    collect data to the prefix
+			# 3) end of buffer does not match any prefix:
+			#    collect data
+			# 4) no terminator, just collect the data
+			if terminator:
+				index = string.find (self.ac_in_buffer, terminator)
+				if index != -1:
+					# we found the terminator
+					self.collect_incoming_data (self.ac_in_buffer[:index])
+					self.ac_in_buffer = self.ac_in_buffer[index+terminator_len:]
+					# This does the Right Thing if the terminator is changed here.
+					self.found_terminator()
+				else:
+					# check for a prefix of the terminator
+					index = find_prefix_at_end (self.ac_in_buffer, terminator)
+					if index:
+						# we found a prefix, collect up to the prefix
+						self.collect_incoming_data (self.ac_in_buffer[:-index])
+						self.ac_in_buffer = self.ac_in_buffer[-index:]
+						break
+					else:
+						# no prefix, collect it all
+						self.collect_incoming_data (self.ac_in_buffer)
+						self.ac_in_buffer = ''
+			else:
+				# no terminator, collect it all
+				self.collect_incoming_data (self.ac_in_buffer)
+				self.ac_in_buffer = ''
+
+	def handle_write (self):
+		self.initiate_send ()
+		
+	def handle_close (self):
+		self.close()
+
+	def push (self, data):
+		self.producer_fifo.push (simple_producer (data))
+		self.initiate_send()
+
+	def push_with_producer (self, producer):
+		self.producer_fifo.push (producer)
+		self.initiate_send()
+
+	def readable (self):
+		return (len(self.ac_in_buffer) <= self.ac_in_buffer_size)
+
+	def writable (self):
+		return len(self.ac_out_buffer) or len(self.producer_fifo) or (not self.connected)
+
+	def close_when_done (self):
+		self.producer_fifo.push (None)
+
+	# refill the outgoing buffer by calling the more() method
+	# of the first producer in the queue
+	def refill_buffer (self):
+		while 1:
+			if len(self.producer_fifo):
+				p = self.producer_fifo.first()
+				# a 'None' in the producer fifo is a sentinel,
+				# telling us to close the channel.
+				if p is None:
+					if not self.ac_out_buffer:
+						self.producer_fifo.pop()
+						self.close()
+					return
+				data = p.more()
+				if data:
+					self.ac_out_buffer = self.ac_out_buffer + data
+					return
+				else:
+					self.producer_fifo.pop()
+			else:
+				return
+
+	def initiate_send (self):
+		obs = self.ac_out_buffer_size
+		# try to refill the buffer
+		if (not self._push_mode) and (len (self.ac_out_buffer) < obs):
+			self.refill_buffer()
+
+		if self.ac_out_buffer and self.connected:
+			# try to send the buffer
+			num_sent = self.send (self.ac_out_buffer[:obs])
+			if num_sent:
+				self.ac_out_buffer = self.ac_out_buffer[num_sent:]
+
+	def discard_buffers (self):
+		# Emergencies only!
+		self.ac_in_buffer = ''
+		self.ac_out_buffer == ''
+		while self.producer_fifo:
+			self.producer_fifo.pop()
+
+	# ==================================================
+	# support for push mode.
+	# ==================================================
+	_push_mode = 0
+	def push_mode (self, boolean):
+		self._push_mode = boolean
+
+	def writable_push (self):
+		return self.connected and len(self.ac_out_buffer)
+
+class simple_producer:
+	def __init__ (self, data, buffer_size=512):
+		self.data = data
+		self.buffer_size = buffer_size
+
+	def more (self):
+		if len (self.data) > self.buffer_size:
+			result = self.data[:self.buffer_size]
+			self.data = self.data[self.buffer_size:]
+			return result
+		else:
+			result = self.data
+			self.data = ''
+			return result
+
+class fifo:
+	def __init__ (self, list=None):
+		if not list:
+			self.list = []
+		else:
+			self.list = list
+		
+	def __len__ (self):
+		return len(self.list)
+
+	def first (self):
+		return self.list[0]
+
+	def push (self, data):
+		self.list.append (data)
+
+	def pop (self):
+		if self.list:
+			result = self.list[0]
+			del self.list[0]
+			return (1, result)
+		else:
+			return (0, None)
+
+# Given 'haystack', see if any prefix of 'needle' is at its end.  This
+# assumes an exact match has already been checked.  Return the number of
+# characters matched.
+# for example:
+# f_p_a_e ("qwerty\r", "\r\n") => 1
+# f_p_a_e ("qwerty\r\n", "\r\n") => 2
+# f_p_a_e ("qwertydkjf", "\r\n") => 0
+
+# this could maybe be made faster with a computed regex?
+
+##def find_prefix_at_end (haystack, needle):
+##	nl = len(needle)
+##	result = 0
+##	for i in range (1,nl):
+##		if haystack[-(nl-i):] == needle[:(nl-i)]:
+##			result = nl-i
+##			break
+##	return result
+
+# yes, this is about twice as fast, but still seems
+# to be neglible CPU.  The previous could do about 290
+# searches/sec. the new one about 555/sec.
+
+import regex
+
+prefix_cache = {}
+
+def prefix_regex (needle):
+	if prefix_cache.has_key (needle):
+		return prefix_cache[needle]
+	else:
+		reg = needle[-1]
+		for i in range(1,len(needle)):
+			reg = '%c\(%s\)?' % (needle[-(i+1)], reg)
+		reg = regex.compile (reg+'$')
+		prefix_cache[needle] = reg, len(needle)
+		return reg, len(needle)
+
+def find_prefix_at_end (haystack, needle):
+	reg, length = prefix_regex (needle)
+	lh = len(haystack)
+	result = reg.search (haystack, max(0,lh-length))
+	if result >= 0:
+		return (lh - result)
+	else:
+		return 0