Boost.Asio documentation is non-existent. What do

问题:

I'm struggling with two errors with Boost.Asio.

The first occurs when I try to receive data on a socket:

char reply[1024];
boost::system::error_code error;
size_t reply_length = s.receive(boost::asio::buffer(reply, 1024), 0, error);
if (error) cout << error.message() << endl; //outputs "End of file"

The second occurs when I try to create an ip::tcp::socket from a (valid!) native socket:

boost::asio::io_service ioserv;
boost::asio::ip::tcp::socket s(ioserv);

boost::system::error_code error;
s.assign(boost::asio::ip::tcp::v4(), nativeSocket, error);
if (error) cout << error.message() << endl; //outputs "The parameter is incorrect"

With all these troubles an no documentation to turn to, I am tempted to go back to BSD sockets, but I'm having my own problems there...so if anyone can help, I'd really appreciate it.

EDIT: Regarding number 2, nativeSocket is declared thusly:

SOCKET nativeSocket = INVALID_SOCKET;
nativeSocket = accept(svr_sock, (struct sockaddr*)&sin, &size);

After that, a few other things are done to the socket -- namely, setting it as non-blocking using ioctlsocket, and using setsockopt for SO_LINGER and SO_OOBINLINE.

回答1:

This is not a complete solution to your second problem by any means. Any errors that it generates should be mapped into a boost::system::error_code, but I don't find anything like it in boost/system/error_code.hpp, so I'm at a loss as to what exactly it is supposed to mean.

But, after looking through the code for boost 1.39, assign is eventually handed off to either detail::reactive_socket_service< Protocol, Reactor >.assign (or detail::win_iocp_socket_service<Protocol>, if you're using windows). It can only be producing an error in two places in boost/asio/detail/reactive_socket_service.hpp:

if (is_open(impl))
{
  ec = boost::asio::error::already_open;
  return ec;
}

or

if (int err = reactor_.register_descriptor(
      native_socket, impl.reactor_data_))
{
  ec = boost::system::error_code(err,
      boost::asio::error::get_system_category());
  return ec;
}

Since, you're not getting an already_open error, the error must from the second bit of code. The reactor type comes from a sequence of ifdef/elif pairs in boost/asio/stream_socket_service.hpp, and of those available only the register_descriptor function in epoll_reactor can throw any error (and of course detail::win_iocp_socket_service<Protocol>.assign can, also). The error in epoll_reactor comes from sys/epoll.h, specifically:

int result = epoll_ctl(epoll_fd_, EPOLL_CTL_ADD, descriptor, &ev);
if (result != 0)
  return errno;

In the windows implementation, the related code is

if (iocp_service_.register_handle(native_socket.as_handle(), ec))
  return ec;

I think this is the origin of your error, but honestly, I can't trace it past this point.