thanos-io/thanos · error

required headers Content-Type and/or…

Error message

required headers Content-Type and/or X-Prometheus-Remote-Write-Version not found

What it means

The fall-through error of determineRWVersion: the remote-write request declares version 2.0.0 via X-Prometheus-Remote-Write-Version but its Content-Type matches none of the accepted protobuf content types (v2 proto, plain x-protobuf, or v1 proto), or the header/content-type combination is otherwise unrecognized. The handler cannot decide which wire format to decode and rejects the write.

Solutions

1. Use a supported Content-Type (application/x-protobuf with a known proto).
2. Check the remote-write client version and headers.

When it happens

Trigger: Thrown at pkg/receive/handler.go:564 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of thanos-io/thanos@35b8b99117 (2026-09-07). Data as JSON: /api/errors/3e88304e42aa797d. Report an issue: GitHub.

Appendix: source

Thrown at pkg/receive/handler.go:564

func determineRWVersion(r *http.Request) (int, error) {
	if r.Header.Get("X-Prometheus-Remote-Write-Version") != "2.0.0" {
		return 1, nil
	}
	ct := r.Header.Get("Content-Type")
	if ct == "" {
		return 0, fmt.Errorf("missing Content-Type header")
	}
	if ct == "application/x-protobuf;proto=io.prometheus.write.v2.Request" {
		return 2, nil
	}
	if ct == "application/x-protobuf" {
		return 1, nil
	}
	if ct == "application/x-protobuf;proto=prometheus.WriteRequest" {
		return 1, nil
	}
	return 0, fmt.Errorf("required headers Content-Type and/or X-Prometheus-Remote-Write-Version not found")
}

func translateV2ToV1(w writev2.Request) *prompb.WriteRequest {
	// TODO(GiedriusS): somehow ensure programmatically that all fields are set and we don't miss anything.
	out := &prompb.WriteRequest{
		Timeseries: make([]prompb.TimeSeries, 0, len(w.Timeseries)),
	}

	for _, t := range w.Timeseries {
		v1Ts := prompb.TimeSeries{}

		v1Ts.Labels = make([]labelpb.ZLabel, 0, len(t.LabelsRefs)/2)
		for i := 0; i+1 < len(t.LabelsRefs); i += 2 {
			v1Ts.Labels = append(v1Ts.Labels, labelpb.ZLabel{
				Name:  w.Symbols[t.LabelsRefs[i]],
				Value: w.Symbols[t.LabelsRefs[i+1]],
			})
		}

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