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Subject: [boost] ASIO does not fully support Windows Runtime (WinRT), and a suggestion for providing support
From: Moshe Rubin (moshe_at_[hidden])
Date: 2015-01-15 05:32:54

While attempting to port filesystem to Windows Phone 8.1, I encountered some issues with the WinRT portions of ASIO. Examining the Boost code shows that ASIO does not fully support WinRT. Examples are that the acceptor implementation for WinRT #includes the null_socket_service class in socket_acceptor_service.hpp, rendering it unsupported. In addition, there is no counterpart in WinRT to WinSock's select() function, so there is no way to call select() off of a WinRT socket object.

I would therefore like to briefly summarize what my company's needs are, what problems I've encountered, and a suggested solution for having ASIO support WinRT.

Here are our corporate library's (let's call it CORLIB) needs:

(*) Our goal is to build our Boost-based library (i.e., CORLIB) for Windows Phone 8.1.
(*) CORLIB refers to Boost sockets in a cross-platform fashion (e.g., using the basic_stream_socket class as an abstraction via boost::asio::ip::tcp::socket).
(*) CORLIB uses the boost::asio::ip::tcp::acceptor object in portions of its code.
(*) CORLIB also calls the bind() socket function
(*) CORLIB uses the BSD/Winsock functions select() and bind(), among other functions, to implement its logic

Here are the problems:

(*) The socket_acceptor_service class #includes null_socket_service.hpp to implement the acceptor object for WinRT. In other words, the acceptor object is not implemented for WinRT.
(*) The winrt_ssocket_service_base class does not implement the listen() function, something that must be implemented to support the acceptor object.
(*) The winrt_ssocket_service class implements native_handle_type as Windows::Networking::Sockets::StreamSocket^. There is no WinRT analog for the BSD/WinSock select() function, so CORLIB has no way of performing a select on the StreamSocket object. Since select() is critical to CORLIB, StreamSocket^ is unacceptable.

We believe that winrt_ssocket_service must be implemented using WinSock (almost completely supported by Windows Phone 8.1) rather than Windows::Networking::Sockets, because the select() function is unimplementable using the WinRT hierarchy.

We therefore propose creating a new socket service class for WinRT (we will refer to this new service class as winrt_winsock_socket_service) . This new service will be similar to reactive_socket_service: the stream_socket_service.hpp include file shows the following:

# include <boost/asio/detail/winrt_ssocket_service.hpp>
#elif defined(BOOST_ASIO_HAS_IOCP)
# include <boost/asio/detail/win_iocp_socket_service.hpp>
# include <boost/asio/detail/reactive_socket_service.hpp>

Since we want to return to WinSock-based sockets for WinRT, we therefore want to model the Winsock-based WinRT implementation on reactive_socket_service, making changes for WinRT when necessary. Because Windows Phone 8.1 supports Winsock2, including bind(), listen(), and select(), we should be able to support WinRT via WinSock. This class will not make any use of WinRT's new socket classes.

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