googleapis/mcp-toolbox · error

error in User Agent retrieval: %s

Error message

error in User Agent retrieval: %s

What it means

This error is returned from the Cloud Monitoring source's Initialize when util.UserAgentFromContext(ctx) cannot extract a User-Agent from the context. The library requires callers to supply a User-Agent through the context, and initialization aborts without one.

Source

Thrown at internal/sources/cloudmonitoring/cloud_monitoring.go:65

	}
	return actual, nil
}

type Config struct {
	Name           string `yaml:"name" validate:"required"`
	Type           string `yaml:"type" validate:"required"`
	UseClientOAuth bool   `yaml:"useClientOAuth"`
}

func (r Config) SourceConfigType() string {
	return SourceType
}

// Initialize initializes a Cloud Monitoring Source instance.
func (r Config) Initialize(ctx context.Context, tracer trace.Tracer) (sources.Source, error) {
	ua, err := util.UserAgentFromContext(ctx)
	if err != nil {
		return nil, fmt.Errorf("error in User Agent retrieval: %s", err)
	}

	var client *http.Client
	if r.UseClientOAuth {
		client = &http.Client{
			Transport: util.NewUserAgentRoundTripper(ua, http.DefaultTransport),
		}
	} else {
		// Use Application Default Credentials
		creds, err := google.FindDefaultCredentials(ctx, monitoring.MonitoringScope)
		if err != nil {
			return nil, fmt.Errorf("failed to find default credentials: %w", err)
		}
		baseClient := oauth2.NewClient(ctx, creds.TokenSource)
		baseClient.Transport = util.NewUserAgentRoundTripper(ua, baseClient.Transport)
		client = baseClient
	}

View on GitHub (pinned to 8cc6e09de2)

Solutions

1. Pass a context containing the User-Agent (use the library's util helpers to inject it)
2. Ensure the HTTP request handling layer forwards the User-Agent header into the context before Initialize
3. If embedding, set the User-Agent explicitly via the same mechanism the toolbox server uses

Example fix

// before
src, err := cfg.Initialize(ctx, tracer) // ctx has no UA
// after
ctx = util.ContextWithUserAgent(ctx, "my-app/1.0")
src, err := cfg.Initialize(ctx, tracer)

ua, err := util.UserAgentFromContext(ctx)
if err != nil {
    ctx = util.ContextWithUserAgent(ctx, "my-app/1.0")
}

if _, err := util.UserAgentFromContext(ctx); err != nil {
    log.Printf("User-Agent missing from context: %v", err)
}

When it happens

Trigger: Calling Config.Initialize on a cloudmonitoring source without a User-Agent value present in the passed context (i.e. util.UserAgentFromContext returns an error).

Common situations: Embedding the toolbox source in a custom server without injecting the User-Agent into the request context; constructing sources directly in tests without the expected context key.

Related errors

• failed to find default credentials: %w
• error in User Agent retrieval: %s
• failed to create Cloud Logging Admin client for project %q:
• failed to create logadmin client for project %q: %w
• client-side OAuth is enabled but no access token was provide

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/a1fb5ab7a55d39e3. Report an issue: GitHub.