thanos-io/thanos · error

received status code: 200, unknown response type

Error message

received status code: 200, unknown response type: '%q'

What it means

QueryInstant got a 200 OK but the response's Data.ResultType was none of the result types the client knows how to decode (vector, matrix, scalar, string). The library treats this as an unknown/undecodable response shape and refuses to parse it rather than returning garbage. It almost always indicates an API contract mismatch between the client and the Prometheus/Thanos server.

Solutions

1. Verify the endpoint is a compatible Prometheus/Thanos /api/v1/query implementation; check server version against the thanos/tls promclient version and upgrade the client library if the server is newer.
2. Dump the raw JSON response (curl the same URL) to see what ResultType is actually returned and compare with the handled cases in the client switch.
3. Check for a misbehaving proxy/gateway between the client and Prometheus that alters the response body.
4. If m.Data was empty because of a server-side issue, fix the server or adjust the query so it returns a normal vector/matrix result.

Example fix

// before
client := promclient.NewClientWithDetails("http://incompatible-proxy:9090", true, true, false)
// after
client := promclient.NewClientWithDetails("http://prometheus:9090", true, true, false)
// and pin/upgrade client to match the server API version

// Pre-flight the endpoint's API compatibility
resp, err := http.Get(base + "/api/v1/status/buildinfo")
if err != nil || resp.StatusCode != 200 {
    return fmt.Errorf("endpoint is not a compatible Prometheus API")
}

func isUnknownResultTypeError(err error) bool {
    return err != nil && strings.Contains(err.Error(), "unknown response type")
}

res, _, _, err := api.PromqlQueryInstant(ctx, q, ts)
if err != nil && strings.Contains(err.Error(), "unknown response type") {
    // API contract mismatch: fail fast, don't retry
    return fmt.Errorf("incompatible prometheus endpoint/version: %w", err)
}

When it happens

Trigger: Calling PromqlQueryInstant against a Prometheus/Thanos server that returns a ResultType the client's switch does not handle (newer API surface, proxy injecting different payload, or a response with empty/missing Data where ResultType serializes as an empty string).

Common situations: Pointing the client at a non-Prometheus or incompatible-version endpoint (e.g. newer Thanos Query API with an additional result type), a misconfigured reverse proxy rewriting responses, or an empty Data field due to a server bug.

Related errors

• failed to create matchers cache
• failed to validate prometheus flags
• failed to get prometheus version
• initial external labels query
• no external labels configured on Prometheus server…

AI-assisted analysis of thanos-io/thanos@35b8b99117 (2026-09-07). Data as JSON: /api/errors/248792548669db71. Report an issue: GitHub.

Appendix: source

Thrown at pkg/promclient/promclient.go:499

	// Currently only `vector` and `scalar` types are supported.
	switch m.Data.ResultType {
	case string(parser.ValueTypeVector):
		if err = json.Unmarshal(m.Data.Result, &vectorResult); err != nil {
			return nil, nil, nil, errors.Wrap(err, "decode result into ValueTypeVector")
		}
	case string(parser.ValueTypeScalar):
		vectorResult, err = convertScalarJSONToVector(m.Data.Result)
		if err != nil {
			return nil, nil, nil, errors.Wrap(err, "decode result into ValueTypeScalar")
		}
	default:
		if m.Warnings != nil {
			return nil, nil, nil, errors.Errorf("error: %s, type: %s, warning: %s", m.Error, m.ErrorType, strings.Join(m.Warnings, ", "))
		}
		if m.Error != "" {
			return nil, nil, nil, errors.Errorf("error: %s, type: %s", m.Error, m.ErrorType)
		}
		return nil, nil, nil, errors.Errorf("received status code: 200, unknown response type: '%q'", m.Data.ResultType)
	}

	return vectorResult, m.Warnings, m.Data.Explanation, nil
}

// PromqlQueryInstant performs instant query and returns results in promql.Vector type that is compatible with promql package.
func (c *Client) PromqlQueryInstant(ctx context.Context, base *url.URL, query string, t time.Time, opts QueryOptions) (promql.Vector, []string, error) {
	vectorResult, warnings, _, err := c.QueryInstant(ctx, base, query, t, opts)
	if err != nil {
		return nil, nil, err
	}

	vec := make(promql.Vector, 0, len(vectorResult))

	b := labels.NewScratchBuilder(0)
	for _, e := range vectorResult {
		b.Reset()

View on GitHub (pinned to 35b8b99117)