apache/beam · error

invalid value

Error message

invalid value: %v

What it means

encodeChanDir failed to map a reflect.ChanDir to its v1pb.Type_ChanDir proto counterpart. Only RecvDir, SendDir, and BothDir are valid; any other value indicates corrupt reflect.Type metadata. Note the function returns Type_BOTH alongside the error, so a mishandled caller could silently mis-encode.

Solutions

1. Verify the reflect.Type being encoded is obtained from genuine Go reflect calls (reflect.ChanOf, etc.), not fabricated
2. Check for nil/garbage ChanDir by logging reflect.TypeOf(value).ChanDir() before encoding
3. Update to a current Go toolchain and Beam SDK to rule out reflect incompatibilities
4. Handle the returned error rather than ignoring it, since Type_BOTH is returned with the error

Example fix

// before: ignoring the error
pb, _ := encodeChanDir(t.ChanDir())

// after
pb, err := encodeChanDir(t.ChanDir())
if err != nil {
    return fmt.Errorf("encoding chan type %v: %w", t, err)
}

dir := t.ChanDir()
if dir != reflect.RecvDir && dir != reflect.SendDir && dir != reflect.BothDir {
    return fmt.Errorf("invalid chan dir %v for type %v", dir, t)
}

func validChanDir(d reflect.ChanDir) bool {
    return d == reflect.RecvDir || d == reflect.SendDir || d == reflect.BothDir
}

pb, err := encodeChanDir(t.ChanDir())
if err != nil {
    return fmt.Errorf("cannot encode channel type %v: %w", t, err)
}

When it happens

Trigger: encodeType encodes a channel-typed value whose t.ChanDir() is not one of reflect.RecvDir/SendDir/BothDir — essentially only possible with corrupted reflect metadata or misuse of the internal API with a synthetic dir value.

Common situations: Rarely hit in practice; mostly from direct use of internal graphx encoders or unusual reflect.Type implementations in tests.

Understand the failure class

Background: Invalid enum value errors: "Unknown type", "Invalid scope", "must be one of" — when a string is not on the library's allowed list — this error's family across 23 libraries.

Related errors

• bad combinefn
• bad decode
• bad decoding function
• bad encode
• bad encoding function

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/47daf3ab36144399. Report an issue: GitHub.

Appendix: source

Thrown at sdks/go/pkg/beam/core/runtime/graphx/serialize.go:766

func decodeInts(offsets []int32) []int {
	var ret []int
	for _, elm := range offsets {
		ret = append(ret, int(elm))
	}
	return ret
}

func encodeChanDir(dir reflect.ChanDir) (v1pb.Type_ChanDir, error) {
	switch dir {
	case reflect.RecvDir:
		return v1pb.Type_RECV, nil
	case reflect.SendDir:
		return v1pb.Type_SEND, nil
	case reflect.BothDir:
		return v1pb.Type_BOTH, nil
	default:
		err := errors.Errorf("invalid value: %v", dir)
		return v1pb.Type_BOTH, errors.WithContextf(err, "encoding channel direction")
	}
}

func decodeChanDir(dir v1pb.Type_ChanDir) (reflect.ChanDir, error) {
	switch dir {
	case v1pb.Type_RECV:
		return reflect.RecvDir, nil
	case v1pb.Type_SEND:
		return reflect.SendDir, nil
	case v1pb.Type_BOTH:
		return reflect.BothDir, nil
	default:
		err := errors.Errorf("invalid value: %v", dir)
		return reflect.BothDir, errors.WithContext(err, "decoding channel direction")
	}
}

View on GitHub (pinned to 12126d8942)