Only log reward balances when they change

E.g.:
[cardano-wallet.network:Info:860] [2021-03-30 11:52:36.01 UTC] Reward observer: New values: {c72a6827: 0.000000, eb220e40: 1000000.000000, fb3c13a2: 1000000.000000}

lib/shelley/src/Cardano/Wallet/Shelley/Network.hs

@@ -841,6 +841,7 @@ newRewardBalanceFetcher tr readNodeTip queryRewardQ = do
 data ObserverLog key value
     = MsgWillFetch (Set key)
     | MsgDidFetch (Map key value)
+    | MsgDidChange (Map key value)
     | MsgAddedObserver key
     | MsgRemovedObserver key
     deriving (Eq, Show)
@@ -855,6 +856,10 @@ instance (Ord key, Buildable key, Buildable value)
         [ "Did fetch values "
         , fmt $ mapF m
         ]
+    toText (MsgDidChange m) = mconcat
+        [ "New values: "
+        , fmt $ mapF m
+        ]
     toText (MsgAddedObserver key) = mconcat
         [ "Started observing values for key "
         , pretty key
@@ -876,7 +881,7 @@ instance (Ord key, Buildable key, Buildable value)
 --
 -- If it returns @Just values@, the cache will be set to @values@.
 newObserver
-    :: forall m key value env. (MonadSTM m, Ord key)
+    :: forall m key value env. (MonadSTM m, Ord key, Eq value)
     => Tracer m (ObserverLog key value)
     -> (env -> Set key -> m (Maybe (Map key value)))
     -> m (Observer m key value, env -> m ())
@@ -914,13 +919,16 @@ newObserver tr fetch = do
         -> m ()
     refresh cacheVar observedKeysVar env = do
         keys <- atomically $ readTVar observedKeysVar
+        oldValues <- atomically $ readTVar cacheVar
         traceWith tr $ MsgWillFetch keys
         mvalues <- fetch env keys
 
         case mvalues of
             Nothing -> pure ()
             Just values -> do
                 traceWith tr $ MsgDidFetch values
+                when (oldValues /= values) $
+                    traceWith tr $ MsgDidChange values
                 atomically $ writeTVar cacheVar values
 
 -- | Return a function to run an action only if its single parameter has changed
@@ -1206,7 +1214,7 @@ instance ToText NetworkLayerLog where
         MsgInterpreter interpreter ->
             "Updated the history interpreter: " <> T.pack (show interpreter)
         MsgInterpreterLog msg -> toText msg
-        MsgObserverLog msg -> toText msg
+        MsgObserverLog msg -> "Reward observer: " <> toText msg
 
 instance HasPrivacyAnnotation NetworkLayerLog
 instance HasSeverityAnnotation NetworkLayerLog where
@@ -1226,7 +1234,6 @@ instance HasSeverityAnnotation NetworkLayerLog where
         MsgProtocolParameters{}            -> Info
         MsgLocalStateQueryError{}          -> Error
         MsgLocalStateQueryEraMismatch{}    -> Debug
-        MsgGetRewardAccountBalance{}       -> Info
         MsgAccountDelegationAndRewards{}   -> Info
         MsgDestroyCursor{}                 -> Notice
         MsgWillQueryRewardsForStake{}      -> Info
@@ -1240,6 +1247,8 @@ instance HasSeverityAnnotation NetworkLayerLog where
             | isSlowQuery qry dt           -> Notice
             | otherwise                    -> Debug
         MsgInterpreterLog msg              -> getSeverityAnnotation msg
+        MsgGetRewardAccountBalance{}       -> Debug
+        MsgObserverLog (MsgDidChange _)    -> Info
         MsgObserverLog{}                   -> Debug
 
 

lib/shelley/test/unit/Cardano/Wallet/Shelley/NetworkSpec.hs

@@ -128,6 +128,7 @@ spec = describe "NetworkLayer regression test #1708" $ do
                             [ MsgAddedObserver k
                             , MsgWillFetch $ Set.singleton k
                             , MsgDidFetch $ Map.singleton k v
+                            , MsgDidChange $ Map.singleton k v
                             ]
 
             describe "calling startObserving a second time" $ do