You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: method.go
    path of file: ./repos/docker-ce/components/cli/vendor/google.golang.org/grpc/internal/grpcutil
    
    the code of the file until where you have to start completion: /*
 *
 * Copyright 2018 gRPC authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed t
    
func ContentSubtype(contentType string) (string, bool) {
	if contentType == baseContentType {
		return "", true
	}
	if !strings.HasPrefix(contentType, baseContentType) {
		return "", false
	}
	// guaranteed since != baseContentType and has baseContentType prefix
	switch contentType[len(baseContentType)] {
	case '+', ';':
		// this will return true for "application/grpc+" or "application/grpc;"
		// which the previous validContentType function tested to be valid, so we
		// just say that no content-subtype is specified in this case
		return contentType[len(baseContentType)+1:], true
	default:
		return "", false
	}
}