grafana/k6 · error

failed to parse headers: %w

Error message

failed to parse headers: %w

What it means

The OpenTelemetry output was configured with custom headers (K6_OTEL_HEADERS), and the header list could not be parsed into key=value pairs. getExporter wraps the parseHeaders failure while constructing the metric exporter.

Source

Thrown at internal/output/opentelemetry/exporter.go:38

	// ctx isn't used at any point in the exporter
	// later on, it could be used for the connection timeout
	ctx := context.Background()

	tlsConfig, err := buildTLSConfig(
		cfg.TLSInsecureSkipVerify,
		cfg.TLSCertificate,
		cfg.TLSClientCertificate,
		cfg.TLSClientKey,
	)
	if err != nil {
		return nil, err
	}

	headers := make(map[string]string)
	if cfg.Headers.Valid {
		headers, err = parseHeaders(cfg.Headers.String)
		if err != nil {
			return nil, fmt.Errorf("failed to parse headers: %w", err)
		}
	}

	// if at least valid user was configured, use basic auth
	if cfg.HTTPUsername.Valid {
		auth := []byte(cfg.HTTPUsername.String + ":" + cfg.HTTPPassword.String)
		headers["Authorization"] = fmt.Sprintf("Basic %s", base64.StdEncoding.EncodeToString(auth))
	}

	switch cfg.ExporterProtocol.String {
	case grpcExporterProtocol:
		return buildGRPCExporter(ctx, cfg, tlsConfig, headers)
	case httpExporterProtocol:
		return buildHTTPExporter(ctx, cfg, tlsConfig, headers)
	default:
		return nil, errors.New("unsupported exporter protocol " + cfg.ExporterProtocol.String)
	}
}

View on GitHub (pinned to 01ffac6f24)

Solutions

1. Format headers as comma-separated key=value pairs, e.g. K6_OTEL_HEADERS=key1=value1,key2=value2
2. Use percent-encoding for special characters in keys or values

When it happens

Trigger: Thrown at internal/output/opentelemetry/exporter.go:38 when the library encounters an invalid state.

Common situations: See trigger scenarios.

Understand the failure class

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

AI-assisted analysis of grafana/k6@01ffac6f24 (2026-08-18). Data as JSON: /api/errors/1302ab67fc384ef6. Report an issue: GitHub.