grafana/k6 · error

unsupported compression type %s - this is a bug in k6, pleas

Error message

unsupported compression type %s - this is a bug in k6, please report it

What it means

Raised by pickDecoder when a response's Content-Encoding maps to a CompressionType with no decoder branch. The message states this is an internal k6 defect: a new compression type exists in the enum but no reader was implemented, so it asks the user to report a bug rather than fix config.

Source

Thrown at lib/netext/httpext/compression.go:210

	return result, respErr
}

func pickDecoder(compression CompressionType, rc *readCloser) (io.Reader, error) {
	var decoder io.Reader
	var err error
	switch compression {
	case CompressionTypeDeflate:
		decoder, err = zlib.NewReader(rc)
	case CompressionTypeGzip:
		decoder, err = gzip.NewReader(rc)
	case CompressionTypeZstd:
		decoder, err = zstd.NewReader(rc)
	case CompressionTypeBr:
		decoder = brotli.NewReader(rc)
	default:
		// We have not implemented a compression ... :(
		err = fmt.Errorf(
			"unsupported compression type %s - this is a bug in k6, please report it",
			compression,
		)
	}

	return decoder, err
}

View on GitHub (pinned to 01ffac6f24)

Solutions

  1. Report the issue to the k6 project (github.com/grafana/k6/issues) with the response Content-Encoding
  2. Work around by requesting the resource without that encoding (e.g. adjust Accept-Encoding)
Defensive patterns

Strategy: validation

When it happens

Trigger: Thrown at lib/netext/httpext/compression.go:210 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of grafana/k6@01ffac6f24 (2026-08-18). Data as JSON: /api/errors/8645fe07f44583cd. Report an issue: GitHub.