elsa-workflows/elsa-core · error · InvalidDataException

Unexpected end of protobuf payload.

Error message

Unexpected end of protobuf payload.

What it means

ReadVarint decodes at most 10 continuation bytes of a base-128 varint. If the remaining buffer empties before a terminating byte (high bit clear) is found, the payload is truncated, and the parser throws InvalidDataException with this message.

Solutions

1. Ensure the full request body is sent (check Content-Length vs actual bytes, disable body-buffering limits on proxies).
2. Re-send the export; truncation is usually transient network/proxy behavior.
3. If reproducible, capture the raw body and validate it with a protobuf decoder to find where truncation starts.

if (bytes.Length < 2 || bytes[^1] != 0) // heuristic: incomplete final varint
    logger.LogWarning("OTLP payload appears truncated; not sending.");

try { await SendAsync(body); }
catch (InvalidDataException ex) when (ex.Message.Contains("Unexpected end"))
{ logger.LogWarning(ex, "OTLP payload truncated in transit; retrying full export."); }

When it happens

Trigger: A truncated OTLP protobuf payload ends mid-varint: the request body was cut off by a proxy timeout, Content-Length mismatch, or partial write, so the last field header/length varint never completes.

Common situations: Reverse proxy or load balancer buffering limits cutting large exports; exporter retry after connection reset leaves partial bytes; testing with hand-crafted byte arrays that are too short.

Understand the failure class

Background: "cannot parse invalid wire-format data", "cannot unmarshal", "failed unmarshalling": protobuf unmarshal errors explained — this error's family across 10 libraries.

Related errors

• Unsupported protobuf wire type
• Invalid protobuf varint.
• The OTLP timestamp is outside the supported range.
• OpenTelemetry gRPC ingestion is enabled, but no gRPC…
• RequestBodyTooLargeException

AI-assisted analysis of elsa-workflows/elsa-core@fe9217bdfa (2026-09-13). Data as JSON: /api/errors/878cf2bfc477a229. Report an issue: GitHub.

Appendix: source

Thrown at src/modules/Elsa.Diagnostics.OpenTelemetry/Ingestion/HttpProtobuf/OtlpHttpProtobufParser.cs:680

                case ProtobufWireType.Fixed32:
                    EnsureAvailable(4);
                    _remaining = _remaining[4..];
                    field = new ProtobufField(number, wireType, default, default, default);
                    return true;
                default:
                    throw new InvalidDataException($"Unsupported protobuf wire type '{wireType}'.");
            }
        }

        private ulong ReadVarint()
        {
            ulong value = 0;
            var shift = 0;

            for (var i = 0; i < 10; i++)
            {
                if (_remaining.IsEmpty)
                    throw new InvalidDataException("Unexpected end of protobuf payload.");

                var b = _remaining[0];
                _remaining = _remaining[1..];
                value |= (ulong)(b & 0x7f) << shift;

                if ((b & 0x80) == 0)
                    return value;

                shift += 7;
            }

            throw new InvalidDataException("Invalid protobuf varint.");
        }

        private readonly void EnsureAvailable(int byteCount)
        {
            if (_remaining.Length < byteCount)
                throw new InvalidDataException("Unexpected end of protobuf payload.");

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