grafana/k6 · error

unknown responseType %s

Error message

unknown responseType %s

What it means

Raised by readResponseBody when the responseType option does not match the known ResponseTypeText or ResponseTypeBinary cases — i.e. an invalid value was passed for how to represent the response body.

Source

Thrown at lib/netext/httpext/compression.go:190

	if err != nil && respErr == nil { // Don't overwrite previous errors
		respErr = wrapDecompressionError(err)
	}

	var result any
	// Binary or string
	switch respType {
	case ResponseTypeText:
		result = buf.String()
	case ResponseTypeBinary:
		// Copy the data to a new slice before we return the buffer to the pool,
		// because buf.Bytes() points to the underlying buffer byte slice.
		// The ArrayBuffer wrapping will be done in the js/modules/k6/http
		// package to avoid a reverse dependency, since it depends on Sobek.
		binData := make([]byte, buf.Len())
		copy(binData, buf.Bytes())
		result = binData
	default:
		respErr = fmt.Errorf("unknown responseType %s", respType)
	}

	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:

View on GitHub (pinned to 01ffac6f24)

Solutions

1. Use responseType: "text" or responseType: "binary"
2. Check for typos such as "string" or "blob" instead of the supported names

When it happens

Trigger: Thrown at lib/netext/httpext/compression.go:190 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/74cbce98b64a671a. Report an issue: GitHub.