From 9f89df6d1cbcafc5feaf4271cfacb4abdc6d740c Mon Sep 17 00:00:00 2001
From: Peter Surda <surda@economicsofbitcoin.com>
Date: Mon, 16 Jan 2017 17:08:47 +0100
Subject: [PATCH] Expire objects that we're unable to receive

- sometimes a node would send an "inv" about an object but then not
  provide it when requested. This could be that it expired in the
  meantime or it was an attack or a bug. This patch will forget that the
  object exists if was requested too many times and not received.
---
 src/inventory.py | 26 ++++++++++++++++++++++----
 1 file changed, 22 insertions(+), 4 deletions(-)

diff --git a/src/inventory.py b/src/inventory.py
index 8b2f6e26..8a747d4b 100644
--- a/src/inventory.py
+++ b/src/inventory.py
@@ -91,7 +91,10 @@ class Missing(object):
         self.lock = RLock()
         self.hashes = {}
         self.stopped = False
+        # don't request the same object more frequently than this
         self.frequency = 60
+        # after requesting and not receiving an object more than this times, consider it expired
+        self.maxRequestCount = 6
         self.pending = {}
 
     def add(self, objectHash):
@@ -99,7 +102,7 @@ class Missing(object):
             return
         with self.lock:
             if objectHash not in self.hashes:
-                self.hashes[objectHash] = {'peers':[], 'requested':0}
+                self.hashes[objectHash] = {'peers':[], 'requested':0, 'requestedCount':0}
             self.hashes[objectHash]['peers'].append(current_thread().peer)
 
     def addPending(self, objectHash=None):
@@ -144,16 +147,31 @@ class Missing(object):
                     self.pending[current_thread().peer]['received'] >= time.time() - self.frequency) and \
                     len(self.pending[current_thread().peer]['objects']) >= count:
                     break
-                # requested too long ago or not at all
+                # requested too long ago or not at all from any thread
                 if self.hashes[objectHash]['requested'] < time.time() - self.frequency:
-                    # already requested from this thread but haven't received yet
+                    # ready requested from this thread but haven't received yet
                     if objectHash in self.pending[current_thread().peer]['objects']:
-                        if self.pending[current_thread().peer]['requested'] >= time.time() - self.frequency or self.pending[current_thread().peer]['received'] >= time.time() - self.frequency:
+                        # if still sending or receiving, request next
+                        if self.pending[current_thread().peer]['received'] >= time.time() - self.frequency or \
+                            self.pending[current_thread().peer]['requested'] >= time.time() - self.frequency:
                             continue
+                        # haven't requested or received anything recently, re-request (i.e. continue)
+                    # the current node doesn't have the object
                     elif current_thread().peer not in self.hashes[objectHash]['peers']:
                         continue
+                    # already requested too many times, remove all signs of this object
+                    if self.hashes[objectHash]['requestedCount'] >= self.maxRequestCount:
+                        with self.lock:
+                            del self.hashes[objectHash]
+                            for thread in self.pending.keys():
+                                if objectHash in self.pending[thread]['objects']:
+                                    self.pending[thread]['objects'].remove(objectHash)
+                        continue
+                    # all ok, request
                     objectHashes.append(objectHash)
                     self.hashes[objectHash]['requested'] = time.time()
+                    with self.lock:
+                        self.hashes[objectHash]['requestedCount'] += 1
                     self.pending[current_thread().peer]['requested'] = time.time()
                     self.addPending(objectHash)
         except (RuntimeError, KeyError, ValueError):