What causes "error decoding single byte field" in apache/beam?

Confirm input data integrity and completeness.

error decoding single byte field

Error message

error decoding single byte field

What it means

Wrap added by reflectDecodeByte in the reflective row decoder when DecodeByte fails reading a single-byte field from the element stream. The underlying cause is an I/O error or truncated/corruptly encoded row bytes; the wrap identifies that the failing field was a byte-sized unsigned field.

Solutions

Confirm input data integrity and completeness.
Re-encode the data with the current coder.
Ensure writer and reader schemas match.
Inspect the stream position for mid-row truncation.

Defensive patterns

Strategy: try-catch

Try / catch

if err := decoderFn(rv, r); err != nil {
    var wrapped error
    if errors.As(err, &wrapped) && strings.Contains(err.Error(), "single byte field") {
        return fmt.Errorf("truncated or corrupt byte field in row: %w", err)
    }
    return err
}

Prevention

Check file sizes/record counts before decoding batches.
Re-encode data after coder or schema changes.
Never decode bytes not produced by the matching Beam encoder.
Log read offsets for corruption triage.

When it happens

Trigger: reflectDecodeByte during row decoding when DecodeByte cannot read one byte: truncated stream, corrupt input, or misaligned decode of differently-coded data.

Common situations: Truncated Beam-encoded files, mixing data encoded with different field orders or coder versions.

Understand the failure class

Background: "failed to read file", EACCES, ENOENT and "could not read <path>" errors: when a program can't read a file from disk — this error's family across 49 libraries.

Related errors

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/b12c6854306bf5e4. Report an issue: GitHub.

Appendix: source

Thrown at sdks/go/pkg/beam/core/graph/coder/row_decoder.go:211

			}
		}
		return nil
	}, nil
}

func reflectDecodeBool(rv reflect.Value, r io.Reader) error {
	v, err := DecodeBool(r)
	if err != nil {
		return errors.Wrap(err, "error decoding bool field")
	}
	rv.SetBool(v)
	return nil
}

func reflectDecodeByte(rv reflect.Value, r io.Reader) error {
	b, err := DecodeByte(r)
	if err != nil {
		return errors.Wrap(err, "error decoding single byte field")
	}
	rv.SetUint(uint64(b))
	return nil
}

func reflectDecodeString(rv reflect.Value, r io.Reader) error {
	v, err := DecodeStringUTF8(r)
	if err != nil {
		return errors.Wrap(err, "error decoding string field")
	}
	rv.SetString(v)
	return nil
}

func reflectDecodeInt(rv reflect.Value, r io.Reader) error {
	v, err := DecodeVarInt(r)
	if err != nil {
		return errors.Wrap(err, "error decoding varint field")

View on GitHub (pinned to 12126d8942)