BoundaryML/baml · error

unexpected type for status: %T

Error message

unexpected type for status: %T

What it means

Thrown by httpResponse.Status() when the FFI call succeeded but the decoded result is not a Go int64. The %T verb names the actual type. The BAML core encodes HTTP status as an integer; a different decoded type signals encoding drift or an unexpected payload from the core.

Source

Thrown at engine/language_client_go/pkg/rawobjects_http_response.go:49

	}

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

	return id, nil
}

func (h *httpResponse) Status() (int64, error) {
	result, err := raw_objects.CallMethod(h, "status", nil)
	if err != nil {
		return 0, fmt.Errorf("failed to get status: %w", err)
	}

	status, ok := result.(int64)
	if !ok {
		return 0, fmt.Errorf("unexpected type for status: %T", result)
	}

	return status, nil
}

func (h *httpResponse) Headers() (map[string]string, error) {
	result, err := raw_objects.CallMethod(h, "headers", nil)
	if err != nil {
		return nil, fmt.Errorf("failed to get headers: %w", err)
	}

	headers, ok := result.(map[string]string)
	if !ok {
		return nil, fmt.Errorf("unexpected type for headers: %T", result)
	}

	return headers, nil
}

View on GitHub (pinned to bd85ce9dee)

Solutions

1. Upgrade the Go bindings and BAML core to matching versions
2. Read the %T in the error to identify what arrived and check pkg/cffi integer decoding
3. Cast defensively only after verifying the type via errors message inspection
4. File an issue with BAML including the %T value if versions match

Example fix

status, err := resp.Status()
if err != nil {
    return fmt.Errorf("non-integer status decoded: %w", err)
}

if resp == nil { return errors.New("nil HTTPResponse") }

status, err := resp.Status()
if err != nil {
    if strings.Contains(err.Error(), "unexpected type") {
        return 0, fmt.Errorf("status decode drift: %w", err)
    }
    return 0, err
}

When it happens

Trigger: Calling HTTPResponse.Status() when the core returns the status as a non-int64 CFFI value — typically from a version mismatch between the Rust core and the Go bindings, or a decoder bug mapping the status field.

Common situations: Partially upgraded BAML installations; reading objects produced by a different engine version; hand-rolled or patched bindings that changed the status encoding.

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 class property builders: %T
• unexpected type for class property builder: %T
• unexpected type for class property type: %T
• unexpected type for body: %T
• unexpected type for id: %T

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/fe7518c8ba16a015. Report an issue: GitHub.