Implemented loop detection for pathfinding and congestionn avoidance for announce rebroadcasts.

RNS/Transport.py

@@ -19,12 +19,19 @@ class Transport:
 	REACHABILITY_DIRECT      = 0x01
 	REACHABILITY_TRANSPORT	 = 0x02
 
+	# TODO: Document the addition of random windows
+	# and max local rebroadcasts.
 	PATHFINDER_M    = 18		# Max hops
 	PATHFINDER_C    = 2.0		# Decay constant
 	PATHFINDER_R	= 2			# Retransmit retries
 	PATHFINDER_T	= 10		# Retry grace period
+	PATHFINDER_RW   = 10		# Random window for announce rebroadcast
 	PATHFINDER_E    = 60*15		# Path expiration in seconds
 
+	# TODO: Calculate an optimal number for this in
+	# various situations
+	LOCAL_REBROADCASTS_MAX = 2	# How many local rebroadcasts of an announce is allowed
+
 	interfaces	 	= []		# All active interfaces
 	destinations    = []		# All active destinations
 	pending_links   = []		# Links that are being established
@@ -32,8 +39,8 @@ class Transport:
 	packet_hashlist = []		# A list of packet hashes for duplicate detection
 	receipts		= []		# Receipts of all outgoing packets for proof processing
 
-	announce_table    = {}
+	announce_table    = {}		# A table for storing announces currently waiting to be retransmitted
-	destination_table = {}
+	destination_table = {}		# A lookup table containing the next hop to a given destination
 
 	jobs_locked = False
 	jobs_running = False
@@ -113,8 +120,7 @@ class Transport:
 							break
 						else:
 							if time.time() > announce_entry[1]:
-								# RNS.log("Rebroadcasting announce", RNS.LOG_INFO)
+								announce_entry[1] = time.time() + math.pow(Transport.PATHFINDER_C, announce_entry[4]) + Transport.PATHFINDER_T + Transport.PATHFINDER_RW
-								announce_entry[1] = time.time() + math.pow(Transport.PATHFINDER_C, announce_entry[4]) + Transport.PATHFINDER_T
 								announce_entry[2] += 1
 								packet = announce_entry[5]
 								announce_data = packet.data
@@ -224,9 +230,18 @@ class Transport:
 						# announce in question from our pending table
 						if packet.destination_hash in Transport.announce_table:
 							announce_entry = Transport.announce_table[packet.destination_hash]
+							
+							if packet.hops == announce_entry[4]:
+								RNS.log("Heard a local rebroadcast of announce for "+RNS.prettyhexrep(packet.destination_hash), RNS.LOG_DEBUG)
+								announce_entry[6] += 1
+								if announce_entry[6] >= Transport.LOCAL_REBROADCASTS_MAX:
+									RNS.log("Max local rebroadcasts of announce for "+RNS.prettyhexrep(packet.destination_hash)+" reached, dropping announce from our table", RNS.LOG_DEBUG)
+									Transport.announce_table.pop(packet.destination_hash)
+
 							if packet.hops == announce_entry[4]+1 and announce_entry[2] > 0:
 								now = time.time()
 								if now < announce_entry[1]:
+									RNS.log("Rebroadcasted announce for "+RNS.prettyhexrep(packet.destination_hash)+" has been passed on to next node, no further tries needed", RNS.LOG_DEBUG)
 									Transport.announce_table.pop(packet.destination_hash)
 
 					else:
@@ -236,22 +251,44 @@ class Transport:
 					# announce and destination tables
 					should_add = False
 					packet.hops += 1
+					# First, check that the announce is not for a destination
+					# local to this system, and that hops are less than the max
 					if (not any(packet.destination_hash == d.hash for d in Transport.destinations) and packet.hops < Transport.PATHFINDER_M+1):
+						random_blob = packet.data[RNS.Identity.DERKEYSIZE/8+10:RNS.Identity.DERKEYSIZE/8+20]
+						random_blobs = []
 						if packet.destination_hash in Transport.destination_table:
-							if packet.hops <= Transport.destination_table[packet.destination_hash][2]:
+							random_blobs = Transport.destination_table[packet.destination_hash][4]
+
 							# If we already have a path to the announced
 							# destination, but the hop count is equal or
 							# less, we'll update our tables.
+							if packet.hops <= Transport.destination_table[packet.destination_hash][2]:
+								# Make sure we haven't heard the random
+								# blob before, so announces can't be
+								# replayed to forge paths.
+								# TODO: Check whether this approach works
+								# under all circumstances
+								if not random_blob in random_blobs:
 									should_add = True
+								else:
+									should_add = False
 							else:
 								# If an announce arrives with a larger hop
 								# count than we already have in the table,
 								# ignore it, unless the path is expired
-								if (time.time() < Transport.destination_table[packet.destination_hash][3]):
+								if (time.time() > Transport.destination_table[packet.destination_hash][3]):
+									# We also check that the announce hash is
+									# different from ones we've already heard,
+									# to avoid loops in the network
+									if not random_blob in random_blobs:
+										# TODO: Check that this ^ approach actually
+										# works under all circumstances
 										RNS.log("Replacing destination table entry for "+str(RNS.prettyhexrep(packet.destination_hash))+" with new announce due to expired path", RNS.LOG_DEBUG)
 										should_add = True
 									else:
 										should_add = False
+								else:
+									should_add = False
 						else:
 							# If this destination is unknown in our table
 							# we should add it
@@ -261,9 +298,11 @@ class Transport:
 							now = time.time()
 							retries = 0
 							expires = now + Transport.PATHFINDER_E
-							retransmit_timeout = now + math.pow(Transport.PATHFINDER_C, packet.hops)
+							local_rebroadcasts = 0
-							Transport.announce_table[packet.destination_hash] = [now, retransmit_timeout, retries, received_from, packet.hops, packet]
+							random_blobs.append(random_blob)
-							Transport.destination_table[packet.destination_hash] = [now, received_from, packet.hops, expires]
+							retransmit_timeout = now + math.pow(Transport.PATHFINDER_C, packet.hops) + (RNS.rand() * Transport.PATHFINDER_RW)
+							Transport.announce_table[packet.destination_hash] = [now, retransmit_timeout, retries, received_from, packet.hops, packet, local_rebroadcasts]
+							Transport.destination_table[packet.destination_hash] = [now, received_from, packet.hops, expires, random_blobs]
 			
 			elif packet.packet_type == RNS.Packet.LINKREQUEST:
 				for destination in Transport.destinations:

RNS/__init__.py

@@ -2,6 +2,7 @@ import os
 import sys
 import glob
 import time
+import random
 
 from .Reticulum import Reticulum
 from .Identity import Identity
@@ -32,6 +33,8 @@ logfile      = None
 logdest      = LOG_STDOUT
 logtimefmt   = "%Y-%m-%d %H:%M:%S"
 
+random.seed(os.urandom(10))
+
 def loglevelname(level):
 	if (level == LOG_CRITICAL):
 		return "Critical"
@@ -66,6 +69,10 @@ def log(msg, level=3):
 			file.write(logstring+"\n")
 			file.close()
 
+def rand():
+	result = random.random()
+	return result
+
 def hexprint(data):
 	print(hexrep(hexrep))