BoundaryML/baml · error

failed to get mime type: %w

Error message

failed to get mime type: %w

What it means

This error wraps any failure returned by the underlying FFI call to the Rust runtime's `mime_type` method on a media object (image, audio, PDF, or video). It is raised by the `MimeType()` method of the Go BAML client's media holder when `raw_objects.CallMethod` reports an error. The original cause (e.g. the runtime object was invalid or the method failed) is preserved via %w, so inspect the wrapped error for details.

Source

Thrown at engine/language_client_go/pkg/rawobjects_media.go:86

	}
}

func (m *mediaHolder) ObjectType() cffi.BamlObjectType {
	return m.mediaType.objectType()
}

func (m *mediaHolder) MediaType() (MediaType, error) {
	return m.mediaType, nil
}

func (m *mediaHolder) pointer() int64 {
	return m.RawObject.Pointer()
}

func (m *mediaHolder) MimeType() (*string, error) {
	result, err := raw_objects.CallMethod(m, "mime_type", nil)
	if err != nil {
		return nil, fmt.Errorf("failed to get mime type: %w", err)
	}

	if result == nil {
		return nil, nil
	}

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

	return &as_mime_type, nil
}

func (m *mediaHolder) IsUrl() (bool, error) {
	result, err := raw_objects.CallMethod(m, "is_url", nil)
	if err != nil {
		return false, fmt.Errorf("failed to get is url: %w", err)

View on GitHub (pinned to bd85ce9dee)

Solutions

1. Inspect the wrapped cause with errors.Is/errors.As to find the underlying FFI failure
2. Re-acquire the media object from a fresh BAML function call instead of reusing an old handle
3. Upgrade github.com/boundaryml/baml Go client and the baml-cli runtime so versions match
4. Log media.MediaType() and the object pointer before the call to confirm the handle is valid

Example fix

// before
mime, err := media.MimeType() // opaque failure
// after
mime, err := media.MimeType()
if err != nil {
    var wrapped error
    if errors.As(err, &wrapped) { log.Printf("mime_type cause: %v", errors.Unwrap(err)) }
    media = reFetchMediaFromResponse() // rebuild handle
}

if media == nil { return fmt.Errorf("media object is nil") }

func validMedia(m baml.Media) bool { var t baml.MediaType; t, err := m.MediaType(); return err == nil && t != "" }

mime, err := media.MimeType()
if err != nil {
    log.Printf("mime type unavailable: %v (cause: %v)", err, errors.Unwrap(err))
    return fallbackMime(media)
}

When it happens

Trigger: Calling MimeType() on an Image, Audio, PDF, or Video instance whose underlying CFFI raw object handle is stale, freed, or whose remote `mime_type` method fails inside the BAML runtime.

Common situations: Holding onto a media object after the runtime response was released; a version mismatch between the Go client and the native BAML runtime; corrupted or unusual media content that the runtime cannot classify.

Understand the failure class

Background: "invalid response format", "malformed payload", "missing data field": when an API returns 200 but the response shape is wrong — this error's family across 23 libraries.

Related errors

• failed to get is url: %w
• failed to get is base64: %w
• failed to get as url: %w
• failed to get as base64: %w
• error decoding type, checked type not found:

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/d4971909a77482c5. Report an issue: GitHub.