BoundaryML/baml · error

failed to decode object response: %w

Error message

failed to decode object response: %w

What it means

This error wraps decodeObjectResponse failures in NewRawObject. The constructor call succeeded and the protobuf unmarshalled, but the response content could not be decoded into a Go object: it may be an error response from the native side, an object handle that cannot be decoded, or a serde value of unexpected shape.

Source

Thrown at engine/language_client_go/baml_go/raw_objects/utils.go:137

	content_bytes := C.GoBytes(unsafe.Pointer(cBuf.ptr), C.int32_t(cBuf.len))
	C.WrapFreeBuffer(cBuf) // Free the buffer after use

	if cBuf.len == 0 {
		return nil, fmt.Errorf("failed to call object constructor")
	}
	if cBuf.ptr == nil {
		return nil, fmt.Errorf("object constructor returned nil pointer")
	}

	var content_holder cffi.InvocationResponse
	err = proto.Unmarshal(content_bytes, &content_holder)
	if err != nil {
		return nil, fmt.Errorf("failed to unmarshal content bytes: %w", err)
	}
	parsed, err := decodeObjectResponse(rt, &content_holder)
	if err != nil {
		return nil, fmt.Errorf("failed to decode object response: %w", err)
	}

	return parsed, nil
}

func destructor(object RawPointer) error {
	result, err := CallMethod(object, "~destructor", nil)

	if err != nil {
		return fmt.Errorf("failed to call destructor: %w", err)
	}

	if result != nil {
		return fmt.Errorf("destructor returned unexpected result: %v", result)
	}
	return nil
}

View on GitHub (pinned to bd85ce9dee)

Solutions

1. Read the wrapped %w message; it usually contains the actual native-side error text
2. Verify all required constructor kwargs (e.g. media url/base64) are valid before calling
3. Reinstall matching versions of the BAML native library and Go module
4. If the message is 'decodeRawObjectImpl is not set', ensure the baml_go runtime was initialized before use

if rt == nil { return fmt.Errorf("runtime required") } // and validate constructor kwargs (url/base64 non-empty) before calling

parsed, err := b.NewTypeBuilder(rt)
if err != nil {
    if strings.Contains(err.Error(), "failed to decode object response") {
        return fmt.Errorf("native constructor rejected call: %w", err)
    }
    return err
}

When it happens

Trigger: NewRawObject invoked via NewCollector, NewTypeBuilder, or media constructors when the native constructor returns an InvocationResponse whose payload cannot be decoded (e.g. native-side error string, unknown object type, decodeRawObjectImpl not registered).

Common situations: Constructor rejected the arguments and returned an error payload; Go bindings initialized incorrectly (decode impl missing); object type enum mismatch between native lib and Go bindings.

Understand the failure class

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

• nil response
• failed to decode object at index %d: %w
• failed to decode object handle: %w
• Protobuf decode error: {0}
• Map entry missing key

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/ff66989a459e5964. Report an issue: GitHub.