Capture trace output with traceInTVar

Author: noonio

CHANGELOG.md

@@ -42,6 +42,9 @@ changes.
 - **BREAKING** Enable handling client recover in all head states.
   - See [Issue #1812](https://github.com/cardano-scaling/hydra/issues/1812) and [PR #2217](https://github.com/cardano-scaling/hydra/pull/2217).
 
+- Optimistic approach to statefile corruption by just ignoring invalid JSON
+  lines [#2253](https://github.com/cardano-scaling/hydra/issues/2253)
+
 ## [0.22.4] - 2025-08-05
 
 - Fix API not correctly handling event log rotation. This was evident in not

hydra-node/test/Hydra/PersistenceSpec.hs

@@ -7,14 +7,14 @@ import Test.Hydra.Prelude
 
 import Data.Aeson (Value (..))
 import Data.Aeson qualified as Aeson
-import Data.ByteString qualified as BS
 import Data.Text qualified as Text
-import Hydra.Logging (Verbosity (Verbose), traceWith, withTracer, withTracerOutputTo)
+import Hydra.Logging (Envelope (..), Verbosity (Verbose), withTracer)
 import Hydra.Persistence (Persistence (..), PersistenceIncremental (..), createPersistence, createPersistenceIncremental, loadAll)
 import Hydra.PersistenceLog
 import Test.QuickCheck (checkCoverage, cover, elements, oneof, suchThat, (===))
 import Test.QuickCheck.Gen (listOf)
 import Test.QuickCheck.Monadic (monadicIO, monitor, pick, run)
+import Test.Util (captureTracer)
 
 spec :: Spec
 spec = do
@@ -40,16 +40,15 @@ spec = do
   describe "PersistenceIncremental" $ do
     it "can ignore invalid lines and emits warning" $ do
       withTempDir "hydra-persistence" $ \tmpDir -> do
-        let logFile = tmpDir <> "/tracer.log"
-        withFile logFile WriteMode $ \hdl -> do
-          withTracerOutputTo hdl "persistence-incremental" $ \tracer -> do
-            let fp = tmpDir <> "/data"
-            writeFileBS fp "\"abc\"\n{\"xyz\": "
-            -- traceWith tracer $ FailedToDecodeJson{reason = "show e", filepath = "fp", contents = "show bs"}
-            p <- createPersistenceIncremental tracer fp
-            loadAll p `shouldReturn` ([Aeson.String "abc"] :: [Aeson.Value])
-        logs <- readFileBS logFile
-        logs `shouldSatisfy` BS.isInfixOf "FailedToDecodeJson"
+        (tracer, getTraces) <- captureTracer "persistence-incremental"
+        let fp = tmpDir <> "/data"
+        writeFileBS fp "\"abc\"\n{\"xyz\": "
+        p <- createPersistenceIncremental tracer fp
+        loadAll p `shouldReturn` ([Aeson.String "abc"] :: [Aeson.Value])
+        traces <- getTraces
+        let rightMsg [Envelope{message = FailedToDecodeJson{}}] = True
+            rightMsg _ = False
+        traces `shouldSatisfy` rightMsg
 
     it "can handle empty files" $ do
       withTracer (Verbose "persistence-incremental") $ \tracer -> do

hydra-node/test/Test/Util.hs

@@ -21,6 +21,7 @@ import Data.Aeson (encode)
 import Data.Aeson qualified as Aeson
 import Data.Text qualified as Text
 import Hydra.Ledger.Simple (SimpleTx)
+import Hydra.Logging (Envelope (..), traceInTVar)
 import Hydra.Network (NetworkCallback (..))
 import Hydra.Node (HydraNodeLog)
 import System.IO.Temp (writeSystemTempFile)
@@ -175,3 +176,13 @@ waitMatch waitNext delay match = do
 
   align _ [] = []
   align n (h : q) = h : fmap (Text.replicate n " " <>) q
+
+-- | Create a tracer that captures all messages and a function to retrieve all
+-- traces captured.
+-- XXX: This is duplicated in MithrilSpec in hydra-cluster, but can't (easily)
+-- be moved to the Test Prelude because of the dependency on Hydra.Logging.
+captureTracer :: Text -> IO (Tracer IO a, IO [Envelope a])
+captureTracer namespace = do
+  traces <- newLabelledTVarIO "capture-tracer" []
+  let tracer = traceInTVar traces namespace
+  pure (tracer, readTVarIO traces)