som: handle pruned transactions for slowly updating feeds

pkg/monitoring/source_envelope.go

@@ -43,9 +43,9 @@ func (s *envelopeSourceFactory) NewSource(
 		return nil, fmt.Errorf("expected feedConfig to be of type config.SolanaFeedConfig not %T", feedConfig)
 	}
 	return &envelopeSource{
-		s.client,
-		solanaFeedConfig,
-		s.log,
+		client:     s.client,
+		feedConfig: solanaFeedConfig,
+		log:        s.log,
 	}, nil
 }
 
@@ -57,6 +57,25 @@ type envelopeSource struct {
 	client     ChainReader
 	feedConfig config.SolanaFeedConfig
 	log        commonMonitoring.Logger
+
+	// these values are cached because transactions can be pruned from an RPC node
+	// if no transactions are found and without a cache, the `getJuelsPerLamport` call will block the entire source.Fetch
+	lock                 sync.RWMutex
+	cacheJuelsPerLamport uint64
+}
+
+func (s *envelopeSource) setJuelsPerLamport(v uint64) error {
+	s.lock.Lock()
+	s.cacheJuelsPerLamport = v
+	s.lock.Unlock()
+
+	return nil
+}
+
+func (s *envelopeSource) readJuelsPerLamport() uint64 {
+	s.lock.RLock()
+	s.lock.RUnlock()
+	return s.cacheJuelsPerLamport
 }
 
 func (s *envelopeSource) Fetch(ctx context.Context) (interface{}, error) {
@@ -163,7 +182,9 @@ func (s *envelopeSource) getJuelsPerLamport(ctx context.Context) (*big.Int, erro
 		return nil, fmt.Errorf("failed to fetch tx signatures for state account '%s': %w", s.feedConfig.StateAccountBase58, err)
 	}
 	if len(txSigs) == 0 {
-		return nil, fmt.Errorf("found no transactions from state account '%s'", s.feedConfig.StateAccountBase58)
+		val := s.readJuelsPerLamport()
+		s.log.Warnw("no transactions found, falling back to cached value - history may have been pruned (cached_value=0 indicates pruned txs encountered on startup)", "state_account", s.feedConfig.StateAccountBase58, "cached_value", val)
+		return new(big.Int).SetUint64(val), nil
 	}
 	for _, txSig := range txSigs {
 		if txSig.Err != nil {
@@ -197,11 +218,11 @@ func (s *envelopeSource) getJuelsPerLamport(ctx context.Context) (*big.Int, erro
 			if !isNewTransmission {
 				continue
 			}
+			// don't block on zero value - handling zero values should happen on the consumer
 			if newTransmission.JuelsPerLamport == 0 {
-				s.log.Infow("zero value for juels/lamport feed is not supported")
-				continue
+				s.log.Warnw("zero value for juels/lamport feed is not supported")
 			}
-			return new(big.Int).SetUint64(newTransmission.JuelsPerLamport), nil
+			return new(big.Int).SetUint64(newTransmission.JuelsPerLamport), s.setJuelsPerLamport(newTransmission.JuelsPerLamport)
 		}
 	}
 	return nil, fmt.Errorf("no correct NewTransmission event found in the last %d transactions on contract state '%s'", txSigsPageSize, s.feedConfig.StateAccountBase58)

pkg/monitoring/source_envelope_test.go

@@ -10,11 +10,14 @@ import (
 	bin "github.com/gagliardetto/binary"
 	"github.com/gagliardetto/solana-go"
 	"github.com/gagliardetto/solana-go/rpc"
+	"github.com/smartcontractkit/chainlink/v2/core/logger"
 	"github.com/smartcontractkit/libocr/offchainreporting2/types"
 	"github.com/stretchr/testify/mock"
 	"github.com/stretchr/testify/require"
+	"go.uber.org/zap/zapcore"
 
 	commonMonitoring "github.com/smartcontractkit/chainlink-common/pkg/monitoring"
+	"github.com/smartcontractkit/chainlink-common/pkg/utils/tests"
 
 	"github.com/smartcontractkit/chainlink-solana/pkg/monitoring/mocks"
 	"github.com/smartcontractkit/chainlink-solana/pkg/monitoring/testutils"
@@ -144,7 +147,7 @@ func TestEnvelopeSource(t *testing.T) {
 		mock.Anything, // ctx
 		feedConfig.StateAccount,
 		mock.Anything, // // because it's hard to mock pointer values!
-	).Return(fakeTxSignatures, nil)
+	).Return(fakeTxSignatures, nil).Once()
 	chainReader.On("GetTransaction",
 		mock.Anything, // ctx
 		fakeTxSignatures[0].Signature,
@@ -155,7 +158,8 @@ func TestEnvelopeSource(t *testing.T) {
 	).Return(fakeTxResult, nil)
 
 	// Call Fetch
-	factory := NewEnvelopeSourceFactory(chainReader, testutils.NewNullLogger())
+	lgr, logs := logger.TestLoggerObserved(t, zapcore.DebugLevel)
+	factory := NewEnvelopeSourceFactory(chainReader, lgr)
 	source, err := factory.NewSource(chainConfig, feedConfig)
 	require.NoError(t, err)
 	rawEnvelope, err := source.Fetch(context.Background())
@@ -221,6 +225,23 @@ func TestEnvelopeSource(t *testing.T) {
 		AggregatorRoundID:       0x13841a,
 	}
 	require.Equal(t, expectedEnvelope, envelope)
+
+	t.Run("empty tx list should return cached JuelsPerLamport", func(t *testing.T) {
+		chainReader.On("GetSignaturesForAddressWithOpts",
+			mock.Anything,
+			feedConfig.StateAccount,
+			mock.Anything,
+		).Return([]*rpc.TransactionSignature{}, nil).Once() // return empty
+
+		envSource, ok := source.(*envelopeSource)
+		require.True(t, ok)
+		cacheValue := envSource.readJuelsPerLamport()
+
+		v, err := envSource.getJuelsPerLamport(tests.Context(t))
+		require.NoError(t, err)
+		require.Equal(t, cacheValue, v.Uint64())
+		tests.AssertLogEventually(t, logs.FilterLevelExact(zapcore.WarnLevel), "no transactions found, falling back to cached value - history may have been pruned (cached_value=0 indicates pruned txs encountered on startup)")
+	})
 }
 
 func TestGetLinkAvailableForPayment(t *testing.T) {