private void closeSocket(Socket socket) {
        try {
            if (!socket.isClosed()) {
                socket.close();
            }
        } catch (IOException e) {
            onError(new ProxyCacheException("Error closing socket", e));
        }
    }
Checks is cache contains fully cached file for particular url.

@param url an url cache file will be checked for.
@return {@code true} if cache contains fully cached file for passed in parameters url.
VideoCache/src/main/java/com/yc/videocache/HttpProxyCacheServer.java