Implement Socket for Windows (WIP)

[andraantariksa]

This is mostly a work in progress.

[straight-shoota]

This is really great! Thanks for getting this started.

Unfortunately, I expect sockets won't really work until the event loop is ported to win32 (#6957).

[andraantariksa]

@straight-shoota Why the "Windows CI" gives me crystal.obj : error LNK2019: unresolved external symbol WSAStartup referenced in function __crystal_main error in "Link Crystal executable" steps, eventhough I have link it using @[Link("WS2_32")]? I think it only happen for WSAStartup function, the other fuction defined in WS2_32 works fine though.

Code: https://github.com/crystal-lang/crystal/pull/9544/files#diff-f2f9112f7cb72f9c35989628ea179284R43

[kubo]

@andraantariksa

Why the "Windows CI" gives me crystal.obj : error LNK2019: unresolved external symbol WSAStartup referenced in function __crystal_main error in "Link Crystal executable" steps, eventhough I have link it using @[Link("WS2_32")]?

Add ws2_32.lib to https://github.com/crystal-lang/crystal/blob/0.35.1/.github/workflows/win.yml#L167

[andraantariksa]

Thank you @kubo , it solve the problem. Can you explain why the Windows CI passed when WSAStartup is not defined, although I have define bind which also require Ws2_32?

[kubo]

Can you explain why the Windows CI passed when WSAStartup is not defined, although I have define bind which also require Ws2_32?

Just defining bind doesn't require ws2_32. Using bind requires ws2_32. The crystal compiler itself doesn't use bind but use WSAStartup here.

[kubo]

I have some opinions about this PR.

• I think that this PR will not be merged until the event loop is ported to win32. (Implement Socket for Windows (WIP) #9544 (comment))

• Too many duplicated and slightly modified code

  For example in src/socket/tcp_socket.cr:

    {% if flag?(:win32) %}
      def initialize(*, socket : LibC::SOCKET, family : Family = Family::INET)
        super socket, family, Type::STREAM, Protocol::TCP
      end
    {% else %}
      def initialize(*, fd : Int32, family : Family = Family::INET)
        super fd, family, Type::STREAM, Protocol::TCP
      end
    {% end %}

  The difference is only the first named argument. I would add Socket::RawFd and use it as follows in order not to duplicate code.
  In src/socket.cr:

  class Socket < IO
  
    ...
  
    {% if flag?(:win32) %}
      alias RawFd = LibC::SOCKET
      INVALID_RAW_FD = LibC::SOCKET.new(-1)
    {% else %}
      alias RawFd = Int32
      INVALID_RAW_FD = -1
    {% end %}
  
    ...
  
    @volatile_fd : Atomic(RawFd)
  
    def fd : RawFd
      @volatile_fd.get
    end

  In src/socket/tcp_socket.cr:

    def initialize(*, fd : Socket::RawFd, family : Family = Family::INET)
      super fd, family, Type::STREAM, Protocol::TCP
    end

• When a socket function fails, WSAGetLastError() must be used instead of errno.

  In the document about bind:

  a specific error code can be retrieved by calling WSAGetLastError.

  EDITED: The following code doesn't work...
  I would add SocketErrno and Socket::Error.from_socket_errno() and use SocketErrno.value, SocketErrno::ECONNREFUSED and from_socket_errno() in place of Errno.value, Errno::ECONNREFUSED and from_errno().

    {% if flag?(:win32) %}
      class SocketErrno < WinError
        def self.value : self
          WinError.new LibC.WSAGetLastError
        end
        ECONNREFUSED = WinError::WSAECONNREFUSED
        EADDRINUSE = WinError::WSAEADDRINUSE
           ...
      end
    {% else %}
      class SocketErrno < ::Errno
      end
    {% end %}

    def self.from_socket_errno(message : String? = nil, errno : SocketErrno = SocketErrno.value, **opts)
      {% if flag?(:win32) %}
        self.from_winerror(message, errno, **opts)
      {% else %}
        self.from_errno(message, errno, **opts)
      {% end %}
    end

  Well, it may be better to add Socket::Errno instead of SocketErrno. Using Socket::Errno will make the modified code size smaller compared with using SocketError. However I'm afraid of confusion of ::Errno and Socket::Errno in src/socket.cr and src/socket/*.cr.

• src/errno.cr should be reverted. Constants starting with WSA are not errno. They are Windows error codes.

• src/lib_c/x86_64-windows-msvc/c/errno.cr should be reverted. Constants starting with WSA in the file are defined in src/winerror.cr. Newly added errno such as EADDRINUSE(100) are declared in Visual C++ errno.h just because POSIX defines them. Windows socket API uses WSAEADDRINUSE(10048) in place of EADDRINUSE in Unix programs.

I've not tested above code. There may be some flaws.
I'm not a maintainer. Maintainers may have other opinions.

[andraantariksa]

Thank you for your opinion. I have been messed up with the code, I will try to fix it 👍

[kubo]

SocketErrno in #9544 (comment) doesn't work.
I'm an experienced C programmer but a newbie about crystal...

[straight-shoota]

@kubo's remarks are value, but there's probably no need to put much work into polishing this PR right now. I'd even suggest to convert it to a draft. There's probably not much sense to merge this until the event loop is ported.
It's still great to have sockets prepared for win32, but we have to go step by step. And there's no point in premature polishing work.