Test of receiving file descriptors from another process using AF_UNIX

af_unix_recv_fd.py

AUTO_DELETE = False			#Change this to True to delete the socket before usage in case it was never cleaned up for some reason

import socketserver, os, struct
from socket import *

class my_handler(socketserver.StreamRequestHandler):
	def handle(self):		
		print('New request!', self.request)
		while True:
			msg, ancdata, flags, addr = self.request.recvmsg(1024, 1024)
			#Print out message
			print(msg, ancdata, flags, addr)

			#Check if it was fit
			if flags & MSG_TRUNC:
				print('Oh noes! Message was truncated!')

			if flags & MSG_CTRUNC:
				print('Oh noes! Ancillary data was truncated!')
			elif ancdata:
				#Go throuhg ancillary data				
				for cmsg_level, cmsg_type, cmsg_data in ancdata:
					#Make sure we understand it
					assert (cmsg_level, cmsg_type) == (SOL_SOCKET, SCM_RIGHTS)

					#Go through the file descriptors and check them out
					for (fd,) in struct.iter_unpack('I', cmsg_data):
						f = os.fdopen(fd)
						print(f'File descriptor: {fd}   File handle: {f}   Pos: {f.tell()}')
						f.close()

			#If we get an empty message we will close
			if not msg:
				self.request.close()
				print('Closing', self.request)
				return



#socketserver.UnixStreamServer is actually SOCK_STREAM and even though SOCK_DGRAM will not be out of order on most systems it does not guarantee it per definition
#Therefore we will use SOCK_SEQPACKET which is a stream of messages that arrives in order
class my_server(socketserver.ThreadingMixIn, socketserver.UnixStreamServer):
	socket_type = SOCK_SEQPACKET

#Try to remove socket reference before running (yes, we should only do this in case we need to but this is just a PoC)
if AUTO_DELETE:
	try:
		os.unlink('/tmp/fd_test.sock')
	except:
		pass

try:
	server = my_server('/tmp/fd_test.sock', my_handler)
	server.serve_forever()

finally:
	#Clean up
	os.unlink('/tmp/fd_test.sock')