读取直到boost :: asio :: streambuf中的字符串分隔符

Question

我想使用非常方便的Boost async_read_until来读取消息,直到我得到\r\n\r\n分隔符.

我喜欢使用这个分隔符,因为它很容易使用telnet进行调试并生成多行命令.我只是通过两条新线发出命令结束的信号.

我打电话async_read_until是这样的:

void do_read()
{
    boost::asio::async_read_until(m_socket,
                                  m_input_buffer,
                                  "\r\n\r\n",
                                  std::bind(&player::handle_read, this, std::placeholders::_1, std::placeholders::_2));
}

我的处理程序现在看起来像这样:

void handle_read(boost::system::error_code ec, std::size_t nr)
{
    std::cout << "handle_read: ec=" << ec << ", nr=" << nr << std::endl;

    if (ec) {
        std::cout << "  -> emit on_disconnect\n";
    } else {
        std::istream iss(&m_input_buffer);
        std::string msg;
        std::getline(iss, msg);

        std::cout << "dump:\n";
        std::copy(msg.begin(), msg.end(), std::ostream_iterator<int>(std::cout, ", "));
        std::cout << std::endl;

        do_read();
    }
}

我想像std::getline示例一样使用,但在我的系统上,这可以保留\r角色.如您所见,如果我连接到服务器并写入hello加上两个CRLF,我会得到这个转储服务器端:

handle_read: ec=system:0, nr=9
dump:
104, 101, 108, 108, 111, 13, 
                         ^^^ \r here

顺便说一句,这也将保留缓冲区中的下一个新行.所以我认为这std::getline不会对我有用.

我搜索一种方便有效的方式来读取boost::asio::streambuf直到我得到这个\r\n\r\n分隔符.因为我async_read_until一次使用一次,当调用处理程序时,缓冲区应该具有完全和完整的数据不是吗？在我到达之前,你建议阅读\r\n\r\n什么？

Answer 1

该async_read_until()操作将读取的所有数据提交到streambuf的输入序列,该bytes_transferred值将包含直到并包括第一个分隔符的字节数.虽然操作可以读取分隔符之外的更多数据,但可以使用bytes_transferred和分隔符大小来仅提取所需数据.例如,如果cmd1\r\n\r\ncmd2可以从套接字读取,并且async_read_until()使用分隔符启动操作\r\n\r\n,则streambuf的输入序列可以包含cmd1\r\n\r\ncmd2:

    ,--------------- buffer_begin(streambuf.data())
   /   ,------------ buffer_begin(streambuf.data()) + bytes_transferred
  /   /                - delimiter.size()
 /   /       ,------ buffer_begin(streambuf.data()) + bytes_transferred
/   /       /   ,--  buffer_end(streambud.data())
cmd1\r\n\r\ncmd2

因此,可以cmd1从streambuf 提取成一个字符串:

// Extract up to the first delimiter.
std::string command{
  boost::asio::buffers_begin(streambuf.data(), 
  boost::asio::buffers_begin(streambuf.data()) + bytes_transferred
    - delimiter.size()};
// Consume through the first delimiter.
m_input_buffer.consume(bytes_transferred);

下面是一个完整的例子演示构建std::string直接从流缓冲的输入序列:

#include <functional> // std::bind
#include <iostream>
#include <boost/asio.hpp>

const auto noop = std::bind([]{});

int main()
{
  using boost::asio::ip::tcp;
  boost::asio::io_service io_service;

  // Create all I/O objects.
  tcp::acceptor acceptor(io_service, tcp::endpoint(tcp::v4(), 0));
  tcp::socket socket1(io_service);
  tcp::socket socket2(io_service);

  // Connect sockets.
  acceptor.async_accept(socket1, noop);
  socket2.async_connect(acceptor.local_endpoint(), noop);
  io_service.run();
  io_service.reset();

  const std::string delimiter = "\r\n\r\n";

  // Write two commands from socket1 to socket2.
  boost::asio::write(socket1, boost::asio::buffer("cmd1" + delimiter));
  boost::asio::write(socket1, boost::asio::buffer("cmd2" + delimiter));

  // Read a single command from socket2.
  boost::asio::streambuf streambuf;
  boost::asio::async_read_until(socket2, streambuf, delimiter,
    [delimiter, &streambuf](
      const boost::system::error_code& error_code,
      std::size_t bytes_transferred)
    {
      // Verify streambuf contains more data beyond the delimiter. (e.g.
      // async_read_until read beyond the delimiter)
      assert(streambuf.size() > bytes_transferred);

      // Extract up to the first delimiter.
      std::string command{
        buffers_begin(streambuf.data()),
        buffers_begin(streambuf.data()) + bytes_transferred
          - delimiter.size()};

      // Consume through the first delimiter so that subsequent async_read_until
      // will not reiterate over the same data.
      streambuf.consume(bytes_transferred);

      assert(command == "cmd1");
      std::cout << "received command: " << command << "\n"
                << "streambuf contains " << streambuf.size() << " bytes."
                << std::endl;
    }
  );
  io_service.run();
}

输出:

received command: cmd1
streambuf contains 8 bytes.