Exception while receiving data from client - “End of file” error

问题

I am currently working on a client server TCP/IP application using Boost ASIO. The client sends data to the server using the following statement

boost::system::error_code ignored_error; 
boost::asio::write(socket, boost::asio::buffer("Hello World\0"), ignored_error);

The server reads this data as such (from an Asynch. read)

boost::asio::async_read(*sock, boost::asio::buffer(buf_server),boost::bind(&ServerRead,boost::asio::placeholders::error));

Here is where the reading is done

boost::array<char, 158> buf_server;

void ServerRead(const boost::system::error_code& error)
{
    if(!error)
    {
        std::cout << "Message: " << buf_server.data() << std::endl;
    }
    else
    {
        std::cout << "Error occurred." << error.message() << std::endl;
    }
}

However I get the error "End of file". So now I have two questions

How can I resolve this issue. What am i doing wrong here ?
Suppose my buf_server was only 5 characters instead of 158. How could I make my receiver use this buffer only to read the entire data and std::cout it?

回答1:

This behavior should be expected when you instruct an application to read 158 bytes but only 12 are sent. To resolve this you can send a fixed size header indicating the message size, the chat client and server example included in the Asio documentation shows how to accomplish this, an excerpt from the client example:

void handle_connect(const boost::system::error_code& error)
  {
    if (!error)
    {
      boost::asio::async_read(socket_,
          boost::asio::buffer(read_msg_.data(), chat_message::header_length),
          boost::bind(&chat_client::handle_read_header, this,
            boost::asio::placeholders::error));
    }
  }

  void handle_read_header(const boost::system::error_code& error)
  {
    if (!error && read_msg_.decode_header())
    {
      boost::asio::async_read(socket_,
          boost::asio::buffer(read_msg_.body(), read_msg_.body_length()),
          boost::bind(&chat_client::handle_read_body, this,
            boost::asio::placeholders::error));
    }
    else
    {
      do_close();
    }
  }

  void handle_read_body(const boost::system::error_code& error)
  {
    if (!error)
    {
      std::cout.write(read_msg_.body(), read_msg_.body_length());
      std::cout << "\n";
      boost::asio::async_read(socket_,
          boost::asio::buffer(read_msg_.data(), chat_message::header_length),
          boost::bind(&chat_client::handle_read_header, this,
            boost::asio::placeholders::error));
    }
    else
    {
      do_close();
    }
  }

Alternatively, or use a more exotic protocol such as HTTP where you read until encountering a \r\n delimiter.

来源：https://stackoverflow.com/questions/15558223/exception-while-receiving-data-from-client-end-of-file-error

标签

c++

boost-asio