From b06656cbba99d58c6edaf5f8e1444c0b9876a6ba Mon Sep 17 00:00:00 2001
From: behzad nouri <behzadnouri@gmail.com>
Date: Wed, 7 Dec 2022 13:00:23 -0500
Subject: [PATCH] tracks number of gossip push duplicates

The commit tracks number of times duplicates of a CRDS value is received
from gossip push. Following commits will utilize this metric to score
gossip nodes in terms of timeliness of their push messages, in order to
better pick which nodes to prune.
---
 gossip/src/crds.rs | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/gossip/src/crds.rs b/gossip/src/crds.rs
index 14d7d57aaa..7df1b90419 100644
--- a/gossip/src/crds.rs
+++ b/gossip/src/crds.rs
@@ -79,6 +79,7 @@ pub struct Crds {
 
 #[derive(PartialEq, Eq, Debug)]
 pub enum CrdsError {
+    DuplicatePush(/*num dups:*/ u8),
     InsertFailed,
     UnknownStakes,
 }
@@ -115,6 +116,8 @@ pub struct VersionedCrdsValue {
     pub(crate) local_timestamp: u64,
     /// value hash
     pub(crate) value_hash: Hash,
+    /// Number of times duplicates of this value are recevied from gossip push.
+    num_push_dups: u8,
 }
 
 #[derive(Clone, Copy, Default)]
@@ -140,6 +143,7 @@ impl VersionedCrdsValue {
             value,
             local_timestamp,
             value_hash,
+            num_push_dups: 0u8,
         }
     }
 }
@@ -263,17 +267,25 @@ impl Crds {
                 entry.insert(value);
                 Ok(())
             }
-            Entry::Occupied(entry) => {
+            Entry::Occupied(mut entry) => {
                 self.stats.lock().unwrap().record_fail(&value, route);
                 trace!(
                     "INSERT FAILED data: {} new.wallclock: {}",
                     value.value.label(),
                     value.value.wallclock(),
                 );
+                // Identify if the message is outdated (as opposed to
+                // duplicate) by comparing value hashes.
                 if entry.get().value_hash != value.value_hash {
                     self.purged.push_back((value.value_hash, now));
+                    Err(CrdsError::InsertFailed)
+                } else if matches!(route, GossipRoute::PushMessage) {
+                    let entry = entry.get_mut();
+                    entry.num_push_dups = entry.num_push_dups.saturating_add(1);
+                    Err(CrdsError::DuplicatePush(entry.num_push_dups))
+                } else {
+                    Err(CrdsError::InsertFailed)
                 }
-                Err(CrdsError::InsertFailed)
             }
         }
     }