add sending a protocol version, so we can extend the protocol in the future...

ntunnel.py

@@ -241,6 +241,15 @@ async def NoiseForwarder(mode, encrdrwrr, ptpairfun, priv_key, pub_key=None):
 	the pair that is returned by genkeypair.
 	'''
 
+	# Send a protocol version so that in the future we can change how
+	# we interface, and possibly be able to send control messages,
+	# allow the client to pass some misc data to the callback, or to
+	# allow a reverse tunnel, were the client talks to the server,
+	# and waits for the server to "connect" to the client w/ a
+	# connection, e.g. reverse tunnel out behind a nat to allow
+	# incoming connections.
+	protocol_version = 0
+
 	rdr, wrr = await encrdrwrr
 
 	proto = NoiseConnection.from_name(b'Noise_XK_448_ChaChaPoly_SHA256')
@@ -294,6 +303,21 @@ async def NoiseForwarder(mode, encrdrwrr, ptpairfun, priv_key, pub_key=None):
 		enclenfun, _ = _genciphfun(proto.get_handshake_hash(), b'toresp')
 		_, declenfun = _genciphfun(proto.get_handshake_hash(), b'toinit')
 
+	# protocol negotiation
+
+	# send first, then wait for the response
+	pvmsg = protocol_version.to_bytes(1, byteorder='big')
+	encmsg = proto.encrypt(pvmsg)
+	wrr.write(enclenfun(encmsg))
+	wrr.write(encmsg)
+
+	# get the protocol version
+	msg = await rdr.readexactly(2 + 16)
+	tlen = declenfun(msg)
+	rmsg = await rdr.readexactly(tlen - 16)
+	tmsg = msg[2:] + rmsg
+	rpv = proto.decrypt(tmsg)
+
 	async def decses():
 		try:
 			while True:
@@ -1015,6 +1039,25 @@ class TestNoiseFowarder(unittest.TestCase):
 		_, declenfun = _genciphfun(proto.get_handshake_hash(),
 		    b'toinit')
 
+		pversion = 0
+		# Send the protocol version string first
+		encmsg = proto.encrypt(pversion.to_bytes(1, byteorder='big'))
+		writer.write(enclenfun(encmsg))
+		writer.write(encmsg)
+
+		# Read the peer's protocol version
+
+		# find out how much we need to read
+		encmsg = await reader.readexactly(2 + 16)
+		tlen = declenfun(encmsg)
+
+		# read the rest of the message
+		rencmsg = await reader.readexactly(tlen - 16)
+		tmsg = encmsg[2:] + rencmsg
+		rptmsg = proto.decrypt(tmsg)
+
+		self.assertEqual(int.from_bytes(rptmsg, byteorder='big'), pversion)
+
 		# write a test message
 		ptmsg = b'this is a test message that should be a little in length'
 		encmsg = proto.encrypt(ptmsg)