grpc-ecosystem/grpc-gateway · error

not an aggregate type: %s in %s

Error message

not an aggregate type: %s in %s

What it means

Path-traversal error from Registry.resolveFieldPath: while walking a dotted field path, an intermediate component resolved to a non-message field (scalar/enum), yet more path components follow. Only message/group fields can be descended into, so the path like 'scalar_field.sub' is invalid; the error names the offending field and full path.

Source

Thrown at internal/descriptor/services.go:337

func (r *Registry) resolveFieldPath(msg *Message, path string, isPathParam bool) ([]FieldPathComponent, error) {
	if path == "" {
		return nil, nil
	}

	root := msg
	var result []FieldPathComponent
	for i, c := range strings.Split(path, ".") {
		if i > 0 {
			f := result[i-1].Target
			switch f.GetType() {
			case descriptorpb.FieldDescriptorProto_TYPE_MESSAGE, descriptorpb.FieldDescriptorProto_TYPE_GROUP:
				var err error
				msg, err = r.LookupMsg(msg.FQMN(), f.GetTypeName())
				if err != nil {
					return nil, err
				}
			default:
				return nil, fmt.Errorf("not an aggregate type: %s in %s", f.GetName(), path)
			}
		}

		if grpclog.V(2) {
			grpclog.Infof("Lookup %s in %s", c, msg.FQMN())
		}
		f := lookupField(msg, c)
		if f == nil {
			return nil, fmt.Errorf("no field %q found in %s", path, root.GetName())
		}
		result = append(result, FieldPathComponent{Name: c, Target: f})
	}
	return result, nil
}

View on GitHub (pinned to a58a4436a3)

Solutions

1. Remove extra path components after the scalar field, or reorder the path so intermediate components are messages.
2. Verify field names and nesting in the HttpRule variable/selector expression.

When it happens

Trigger: Thrown at internal/descriptor/services.go:337 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of grpc-ecosystem/grpc-gateway@a58a4436a3 (2026-09-02). Data as JSON: /api/errors/d8cb02327b06a558. Report an issue: GitHub.