Merge pull request #2571 from Roasbeef/lnwire-onion-fix

lnwire: ensure we're able to decode legacy FailUnknownPaymentHash

lnwire/onion_error.go

@@ -366,7 +366,20 @@ func (f FailUnknownPaymentHash) Error() string {
 //
 // NOTE: Part of the Serializable interface.
 func (f *FailUnknownPaymentHash) Decode(r io.Reader, pver uint32) error {
-	return ReadElement(r, &f.amount)
+	err := ReadElement(r, &f.amount)
+	switch {
+	// This is an optional tack on that was added later in the protocol. As
+	// a result, older nodes may not include this value. We'll account for
+	// this by checking for io.EOF here which means that no bytes were read
+	// at all.
+	case err == io.EOF:
+		return nil
+
+	case err != nil:
+		return err
+	}
+
+	return nil
 }
 
 // Encode writes the failure in bytes stream.

lnwire/onion_error_test.go

@@ -33,10 +33,10 @@ var onionFailures = []FailureMessage{
 	&FailPermanentChannelFailure{},
 	&FailRequiredChannelFeatureMissing{},
 	&FailUnknownNextPeer{},
-	&FailUnknownPaymentHash{},
 	&FailIncorrectPaymentAmount{},
 	&FailFinalExpiryTooSoon{},
 
+	NewFailUnknownPaymentHash(99),
 	NewInvalidOnionVersion(testOnionHash),
 	NewInvalidOnionHmac(testOnionHash),
 	NewInvalidOnionKey(testOnionHash),
@@ -167,3 +167,30 @@ func TestWriteOnionErrorChanUpdate(t *testing.T) {
 			trueUpdateLength, encodedLen)
 	}
 }
+
+// TestFailUnknownPaymentHashOptionalAmount tests that we're able to decode an
+// UnknownPaymentHash error that doesn't have the optional amount. This ensures
+// we're able to decode FailUnknownPaymentHash messages from older nodes.
+func TestFailUnknownPaymentHashOptionalAmount(t *testing.T) {
+	t.Parallel()
+
+	// Creation an error that is a non-pointer will allow us to skip the
+	// type assertion for the Serializable interface. As a result, the
+	// amount body won't be written.
+	onionError := FailUnknownPaymentHash{}
+
+	var b bytes.Buffer
+	if err := EncodeFailure(&b, onionError, 0); err != nil {
+		t.Fatalf("unable to encode failure: %v", err)
+	}
+
+	onionError2, err := DecodeFailure(bytes.NewReader(b.Bytes()), 0)
+	if err != nil {
+		t.Fatalf("unable to decode error: %v", err)
+	}
+
+	if !reflect.DeepEqual(onionError, onionError) {
+		t.Fatalf("expected %v, got %v", spew.Sdump(onionError),
+			spew.Sdump(onionError2))
+	}
+}