Dandelion updates

- expiration now uses poisson distribution just like in the bitcoin
version

src/network/dandelion.py

@@ -1,5 +1,5 @@
 from collections import namedtuple
-from random import choice, sample
+from random import choice, sample, expovariate
 from threading import RLock
 from time import time
 
@@ -12,8 +12,11 @@
 
 # randomise routes after 600 seconds
 REASSIGN_INTERVAL = 600
-# trigger fluff due to expiration in 2 minutes
-FLUFF_TRIGGER_TIMEOUT = 120
+
+# trigger fluff due to expiration
+FLUFF_TRIGGER_FIXED_DELAY = 10
+FLUFF_TRIGGER_MEAN_DELAY = 30
+
 MAX_STEMS = 2
 
 Stem = namedtuple('Stem', ['child', 'stream', 'timeout'])
@@ -31,22 +34,30 @@ def __init__(self):
         self.refresh = time() + REASSIGN_INTERVAL
         self.lock = RLock()
 
+    @staticmethod
+    def poissonTimeout(start=None, average=0):
+        if start is None:
+            start = time()
+        if average == 0:
+            average = FLUFF_TRIGGER_MEAN_DELAY
+        return start + expovariate(1.0/average) + FLUFF_TRIGGER_FIXED_DELAY
+
     def addHash(self, hashId, source=None, stream=1):
         if not state.dandelion:
             return
         with self.lock:
             self.hashMap[hashId] = Stem(
                     self.getNodeStem(source),
                     stream,
-                    time() + FLUFF_TRIGGER_TIMEOUT)
+                    Dandelion.poissonTimeout())
 
     def setHashStream(self, hashId, stream=1):
         with self.lock:
             if hashId in self.hashMap:
                 self.hashMap[hashId] = Stem(
                         self.hashMap[hashId].child,
                         stream,
-                        time() + FLUFF_TRIGGER_TIMEOUT)
+                        Dandelion.poissonTimeout())
 
     def removeHash(self, hashId, reason="no reason specified"):
         logging.debug("%s entering fluff mode due to %s.", ''.join('%02x'%ord(i) for i in hashId), reason)
@@ -70,7 +81,7 @@ def maybeAddStem(self, connection):
                 for k in (k for k, v in self.nodeMap.iteritems() if v is None):
                     self.nodeMap[k] = connection
                 for k, v in {k: v for k, v in self.hashMap.iteritems() if v.child is None}.iteritems():
-                    self.hashMap[k] = Stem(connection, v.stream, time() + FLUFF_TRIGGER_TIMEOUT)
+                    self.hashMap[k] = Stem(connection, v.stream, Dandelion.poissionTimeout())
                     invQueue.put((v.stream, k, v.child))
 
 
@@ -83,7 +94,7 @@ def maybeRemoveStem(self, connection):
                 for k in (k for k, v in self.nodeMap.iteritems() if v == connection):
                     self.nodeMap[k] = None
                 for k, v in {k: v for k, v in self.hashMap.iteritems() if v.child == connection}.iteritems():
-                    self.hashMap[k] = Stem(None, v.stream, time() + FLUFF_TRIGGER_TIMEOUT)
+                    self.hashMap[k] = Stem(None, v.stream, Dandelion.poissonTimeout())
 
     def pickStem(self, parent=None):
         try: