BoundaryML/baml · error

unexpected type for ID: %T

Error message

unexpected type for ID: %T

What it means

httpRequest.RequestId() expects the runtime 'id' method to return a Go string. 'unexpected type for ID: %T' means the bridge succeeded but returned a different Go type (e.g. nil, float64, map), so the value cannot be safely returned as a string.

Source

Thrown at engine/language_client_go/pkg/rawobjects_http_request.go:35

}

func (h *httpRequest) ObjectType() cffi.BamlObjectType {
	return cffi.BamlObjectType_OBJECT_HTTP_REQUEST
}

func (h *httpRequest) pointer() int64 {
	return h.RawObject.Pointer()
}

func (h *httpRequest) RequestId() (string, error) {
	result, err := raw_objects.CallMethod(h, "id", nil)
	if err != nil {
		return "", fmt.Errorf("failed to get ID: %w", err)
	}

	id, ok := result.(string)
	if !ok {
		return "", fmt.Errorf("unexpected type for ID: %T", result)
	}

	return id, nil
}

func (h *httpRequest) Url() (string, error) {
	result, err := raw_objects.CallMethod(h, "url", nil)
	if err != nil {
		return "", fmt.Errorf("failed to get URL: %w", err)
	}

	url, ok := result.(string)
	if !ok {
		return "", fmt.Errorf("unexpected type for URL: %T", result)
	}

	return url, nil
}

View on GitHub (pinned to bd85ce9dee)

Solutions

1. Fix the runtime/handler so 'id' returns a string
2. Inspect %T in the message to see the actual returned type
3. Add a conversion (e.g. fmt.Sprintf) only if the value is genuinely a non-string ID
4. Verify client and runtime versions agree on the request shape

Example fix

// before
id, err := req.RequestId()
// after
id, err := req.RequestId()
if err != nil && strings.Contains(err.Error(), "unexpected type for ID: float64") {
    log.Printf("runtime returned numeric ID; upgrade runtime or coerce")
}

// Cannot pre-validate; validate after call:
id, err := req.RequestId()
if err == nil && id == "" { /* runtime returned empty/non-string id */ }

func isString(v any) bool { _, ok := v.(string); return ok }

id, err := req.RequestId()
if err != nil {
    if strings.Contains(err.Error(), "unexpected type") {
        return fmt.Errorf("runtime returned non-string ID: %w", err)
    }
    return err
}

When it happens

Trigger: The runtime's 'id' implementation returns a non-string (null, number, object) — e.g. a custom handler or script returning a numeric or absent ID.

Common situations: Custom request handlers/scripts that omit or redefine 'id'; schema changes in the runtime where IDs became numbers; serialization converting the ID type.

Understand the failure class

Background: Type mismatch errors: IllegalArgumentException, TypeError and type guards across 150 open-source libraries — this error's family across 150 libraries.

Related errors

• unexpected type for logs: %T
• unexpected type in logs: %T
• unexpected type for last log: %T %v
• unexpected type for log by id: %T
• unexpected type for clear result: %T

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/78670e983beadbd6. Report an issue: GitHub.