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+This is a simple [[http://en.wikipedia.org/wiki/SOCKS|SOCKSv4 proxy]] written in pure python.  Suitable for use with browsers.
+<code=python>
+#!/usr/bin/python
+import sys
+import socket
+import struct
+import thread
+from optparse import OptionParser
+# Very simple multi-threaded SOCKSv4(a) proxy
+# by Tyler Bletsch (Tyler.Bletsch at gmail dot com)
+parser = OptionParser("Usage: %prog [options]")
+parser.add_option("-p", "--port", dest="listen_port", help="Port on which to listen (default: %default).", metavar="PORT", type="int", default=1080)
+parser.add_option("-l", "--listen-interface", dest="listen_interface", help="IP address of the interface to listen on (default: all of them).", metavar="IP", default='0.0.0.0')
+parser.add_option("-c", "--connect-interface", dest="connect_interface", help="IP address of the interface to connect out with (default: default route).", metavar="IP", default=None)
+parser.add_option("-b", "--buffer-size", dest="buffer_size", help="Size of the forwarding buffer (default: %default).", metavar="N", type="int", default=4096)
+(options, args) = parser.parse_args()
+buffer_size = options.buffer_size
+listen_port = options.listen_port
+listen_interface = options.listen_interface
+connect_interface = options.connect_interface
+def readstr(s):
+	r=''
+	while 1:
+		c = s.recv(1)
+		if not c: return None
+		if c == '\0': break
+		r += c
+	return r
+def tunnel(src,dest):
+	while 1:
+		try:
+			r = src.recv(buffer_size)
+		except Exception as e:
+			print "Recv error: %s" % e
+			src.close()
+			dest.close()
+			break
+		if not r:
+			src.close()
+			dest.close()
+			break
+		try:
+			dest.send(r)
+		except Exception as e:
+			print "Send error: %s" % e
+			src.close()
+			dest.close()
+			break
+svr = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+svr.bind((listen_interface, listen_port))
+svr.listen(32)
+SOCKS4_REQUEST_FORMAT = '!BBH4s' # byte (socks_ver), byte (command), short (port), 4-char string (IP addr)
+SOCKS4_RESPONSE_OKAY = struct.pack('!BBHI',0,0x5a,0,0)
+SOCKS4_RESPONSE_FAIL = struct.pack('!BBHI',0,0x5b,0,0)
+print "Listening on %s:%d..." % (listen_interface,listen_port)
+while 1:
+	initiator, initiator_addr = svr.accept()
+	sys.stdout.write('%16s:%-5d ' % (initiator_addr))
+	data = initiator.recv(struct.calcsize(SOCKS4_REQUEST_FORMAT))
+	if not data:
+		print "Connection dropped."
+		break
+	(socks_ver,command,target_port,target_addr) = struct.unpack(SOCKS4_REQUEST_FORMAT,data)
+	(target_addr_int,) = struct.unpack('!I',target_addr)
+	target_addr = socket.inet_ntoa(target_addr)
+	username = readstr(initiator)
+	if socks_ver!=4:
+		print "Dropping non-SOCKSv4 request."
+		initiator.send(SOCKS4_RESPONSE_FAIL)
+		initiator.close()
+		continue
+	if command!=1:
+		print "Dropping non-connect request."
+		initiator.send(SOCKS4_RESPONSE_FAIL)
+		initiator.close()
+		continue
+	is_socks4a = target_addr_int>0 and target_addr_int<256 # check for 0.0.0.x, i.e. SOCKS4a domain mode
+	if is_socks4a:
+		target_addr = readstr(initiator)
+	sys.stdout.write("SOCKSv4%s => %s:%d  " % ('a' if is_socks4a else ' ', target_addr, target_port))
+	target = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+	if connect_interface: target.bind((connect_interface, 0))
+	try:
+		target.connect((target_addr, target_port))
+	except Exception as e:
+		initiator.send(SOCKS4_RESPONSE_FAIL)
+		initiator.close()
+		print "FAIL: %s" % e
+		continue
+	if not target:
+		initiator.send(SOCKS4_RESPONSE_FAIL)
+		initiator.close()
+		print "FAIL"
+		continue
+	print "OK"
+	initiator.send(SOCKS4_RESPONSE_OKAY)
+	thread.start_new_thread(tunnel,(initiator,target))
+	thread.start_new_thread(tunnel,(target,initiator))
+</code>