Merge #15486: [addrman, net] Ensure tried collisions resolve, and allow feeler connections to existing outbound netgroups

20e6ea259b222b10f066f22695a5f56c52071f63 [addrman] Improve collision logging and address nits (Suhas Daftuar)
f71fdda3bc2e7acd2a8b74e882364866b8b0f55b [addrman] Ensure collisions eventually get resolved (Suhas Daftuar)
4991e3c813c9848d3b3957ea3ad433f02fca9e81 [net] feeler connections can be made to outbound peers in same netgroup (Suhas Daftuar)
4d834018e368c3481a5421891395f64aa9002185 [addrman] Improve tried table collision logging (Suhas Daftuar)

Pull request description:

  The restriction on outbound peers sharing the same network group is not intended to apply to feeler connections, so fix this.

  This fixes an issue where a tried table collision with an entry to a netgroup we already have an outbound connection to could cause feelers to stop working, because the tried collision buffer (`m_tried_collisions`) would never be drained.

  Also, ensure that all entries don't linger in `m_tried_collisions` by evicting an old entry if its collisions is unresolved after 40 minutes.

Tree-SHA512: 553fe2b01b82cd7f0f62f90c6781e373455a45b254e3bec085b5e6b16690aa9f3938e8c50e7136f19dafa250ed4578a26227d944b76daf9ce4ef0c75802389b6

3 files changed, 22 insertions, 4 deletions

diff --git a/src/addrman.cpp b/src/addrman.cpp
index 06c342ba73..8a5f78d1c5 100644
--- a/src/addrman.cpp
+++ b/src/addrman.cpp
@@ -239,7 +239,9 @@ void CAddrMan::Good_(const CService& addr, bool test_before_evict, int64_t nTime
 
     // Will moving this address into tried evict another entry?
     if (test_before_evict && (vvTried[tried_bucket][tried_bucket_pos] != -1)) {
-        LogPrint(BCLog::ADDRMAN, "Collision inserting element into tried table, moving %s to m_tried_collisions=%d\n", addr.ToString(), m_tried_collisions.size());
+        // Output the entry we'd be colliding with, for debugging purposes
+        auto colliding_entry = mapInfo.find(vvTried[tried_bucket][tried_bucket_pos]);
+        LogPrint(BCLog::ADDRMAN, "Collision inserting element into tried table (%s), moving %s to m_tried_collisions=%d\n", colliding_entry != mapInfo.end() ? colliding_entry->second.ToString() : "", addr.ToString(), m_tried_collisions.size());
         if (m_tried_collisions.size() < ADDRMAN_SET_TRIED_COLLISION_SIZE) {
             m_tried_collisions.insert(nId);
         }
@@ -561,12 +563,19 @@ void CAddrMan::ResolveCollisions_()
 
                     // Give address at least 60 seconds to successfully connect
                     if (GetAdjustedTime() - info_old.nLastTry > 60) {
-                        LogPrint(BCLog::ADDRMAN, "Swapping %s for %s in tried table\n", info_new.ToString(), info_old.ToString());
+                        LogPrint(BCLog::ADDRMAN, "Replacing %s with %s in tried table\n", info_old.ToString(), info_new.ToString());
 
                         // Replaces an existing address already in the tried table with the new address
                         Good_(info_new, false, GetAdjustedTime());
                         erase_collision = true;
                     }
+                } else if (GetAdjustedTime() - info_new.nLastSuccess > ADDRMAN_TEST_WINDOW) {
+                    // If the collision hasn't resolved in some reasonable amount of time,
+                    // just evict the old entry -- we must not be able to
+                    // connect to it for some reason.
+                    LogPrint(BCLog::ADDRMAN, "Unable to test; replacing %s with %s in tried table anyway\n", info_old.ToString(), info_new.ToString());
+                    Good_(info_new, false, GetAdjustedTime());
+                    erase_collision = true;
                 }
             } else { // Collision is not actually a collision anymore
                 Good_(info_new, false, GetAdjustedTime());
diff --git a/src/addrman.h b/src/addrman.h
index 003bd059f8..e54184ce35 100644
--- a/src/addrman.h
+++ b/src/addrman.h
@@ -166,6 +166,9 @@ public:
 //! the maximum number of tried addr collisions to store
 #define ADDRMAN_SET_TRIED_COLLISION_SIZE 10
 
+//! the maximum time we'll spend trying to resolve a tried table collision, in seconds
+static const int64_t ADDRMAN_TEST_WINDOW = 40*60; // 40 minutes
+
 /**
  * Stochastical (IP) address manager
  */
diff --git a/src/net.cpp b/src/net.cpp
index 87f1ef0577..ccab4a1718 100644
--- a/src/net.cpp
+++ b/src/net.cpp
@@ -1765,9 +1765,15 @@ void CConnman::ThreadOpenConnections(const std::vector<std::string> connect)
                 addr = addrman.Select(fFeeler);
             }
 
-            // if we selected an invalid address, restart
-            if (!addr.IsValid() || setConnected.count(addr.GetGroup()) || IsLocal(addr))
+            // Require outbound connections, other than feelers, to be to distinct network groups
+            if (!fFeeler && setConnected.count(addr.GetGroup())) {
                 break;
+            }
+
+            // if we selected an invalid or local address, restart
+            if (!addr.IsValid() || IsLocal(addr)) {
+                break;
+            }
 
             // If we didn't find an appropriate destination after trying 100 addresses fetched from addrman,
             // stop this loop, and let the outer loop run again (which sleeps, adds seed nodes, recalculates