BOOST中read_some和 boost::asio::error::eof(2)错误

for (;;) {
    boost::array < char, 128 > buf;
    boost::system::error_code error;
    size_t len = socket.read_some(boost::asio::buffer(buf), boost::asio::assign_error(error));
    //当服务器关闭连接时,boost::asio::ip::tcp::socket::read_some()会用boost::asio::error::eof标志完成, 这时我们应该退出读取循环了. 
    if (error == boost::asio::error::eof)
      break;
    // Connection closed cleanly by peer.
    else if (error)
      throw error;
    // Some other error.
    std::cout.write(buf.data(), len);
}
//如果发生了什么异常我们同样会抛出它