BoundaryML/baml · critical

invalid media type

Error message

invalid media type: '%s'

What it means

MediaType.objectType() maps a MediaType constant to a cffi.BamlObjectType and panics on any value outside Image/Audio/PDF/Video. Because it panics (not returns an error), an unrecognized media type crashes the process at the point of serialization or ObjectType() lookup.

Solutions

1. Only construct MediaType via the exported MediaType_Image/Audio/PDF/Video constants
2. Update all BAML Go packages to the same version so the enum and switch agree
3. Never cast raw integers to MediaType

Example fix

// before
var mt baml.MediaType
media := baml.NewMediaFromBase64(mt, ...)
// after
media := baml.NewMediaFromBase64(baml.MediaType_PDF, ...) // use a valid constant

// Go: validate before use
func validMediaType(mt baml.MediaType) bool {
    switch mt {
    case baml.MediaType_Image, baml.MediaType_Audio, baml.MediaType_PDF, baml.MediaType_Video:
        return true
    }
    return false
}

When it happens

Trigger: Constructing a media holder with a MediaType value not produced by the library's own constants — e.g. a zero-value MediaType{}, a value from a different/older package version, or a custom int cast to MediaType.

Common situations: Upgrading BAML where a new MediaType was added in one package but the mapping switch wasn't regenerated; declaring var m MediaType = 0 and passing it into media constructors.

Understand the failure class

Background: Invalid enum value errors: "Unknown type", "Invalid scope", "must be one of" — when a string is not on the library's allowed list — this error's family across 23 libraries.

Related errors

• unexpected cffi.isCFFIFieldTypeLiteral_Literal: %#v
• unexpected stream state
• ======================================== BAML Internal…
• baml.panics.AssertionFailed
• baml.panics.Cancelled

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/3298332b5b4bd6c0. Report an issue: GitHub.

Appendix: source

Thrown at engine/language_client_go/pkg/rawobjects_media.go:52

// mediaHolder implements InternalBamlSerializer
func (m *mediaHolder) InternalBamlSerializer() {}

func (m *mediaHolder) Encode() (*cffi.BamlObjectHandle, error) {
	return raw_objects.EncodeRawObject(m), nil
}

func (mediaType MediaType) objectType() cffi.BamlObjectType {
	switch mediaType {
	case MediaType_Image:
		return cffi.BamlObjectType_OBJECT_MEDIA_IMAGE
	case MediaType_Audio:
		return cffi.BamlObjectType_OBJECT_MEDIA_AUDIO
	case MediaType_PDF:
		return cffi.BamlObjectType_OBJECT_MEDIA_PDF
	case MediaType_Video:
		return cffi.BamlObjectType_OBJECT_MEDIA_VIDEO
	default:
		panic(fmt.Sprintf("invalid media type: '%s'", mediaType))
	}
}

func (mediaType MediaType) cffiType() (cffi.MediaTypeEnum, error) {
	switch mediaType {
	case MediaType_Image:
		return cffi.MediaTypeEnum_IMAGE, nil
	case MediaType_Audio:
		return cffi.MediaTypeEnum_AUDIO, nil
	case MediaType_PDF:
		return cffi.MediaTypeEnum_PDF, nil
	case MediaType_Video:
		return cffi.MediaTypeEnum_VIDEO, nil
	default:
		return 0, fmt.Errorf("invalid media type: '%s'", mediaType)
	}
}

View on GitHub (pinned to bd85ce9dee)