feat: implement cancellation for read and write socket operations

- Add do_cancel() implementation for read_op using CancelIoEx
- Add do_cancel() implementation for write_op using CancelIoEx
- Add win_socket_impl reference to read_op and write_op structs
- Initialize read and write operations with socket impl in constructor

Author: vinniefalco

src/detail/win_iocp_sockets.cpp

@@ -87,9 +87,35 @@ do_cancel() noexcept
     }
 }
 
+void
+read_op::
+do_cancel() noexcept
+{
+    if (impl.is_open())
+    {
+        ::CancelIoEx(
+            reinterpret_cast<HANDLE>(impl.native_handle()),
+            this);
+    }
+}
+
+void
+write_op::
+do_cancel() noexcept
+{
+    if (impl.is_open())
+    {
+        ::CancelIoEx(
+            reinterpret_cast<HANDLE>(impl.native_handle()),
+            this);
+    }
+}
+
 win_socket_impl::
 win_socket_impl(win_iocp_sockets& svc) noexcept
     : svc_(svc)
+    , rd_(*this)
+    , wr_(*this)
 {
 }
 

src/detail/win_iocp_sockets.hpp

@@ -49,8 +49,12 @@ struct read_op : overlapped_op
     WSABUF wsabufs[max_buffers];
     DWORD wsabuf_count = 0;
     DWORD flags = 0;
+    win_socket_impl& impl;
+
+    explicit read_op(win_socket_impl& impl_) noexcept : impl(impl_) {}
 
     bool is_read_operation() const noexcept override { return true; }
+    void do_cancel() noexcept override;
 };
 
 /** Write operation state with buffer descriptors. */
@@ -59,6 +63,11 @@ struct write_op : overlapped_op
     static constexpr std::size_t max_buffers = 16;
     WSABUF wsabufs[max_buffers];
     DWORD wsabuf_count = 0;
+    win_socket_impl& impl;
+
+    explicit write_op(win_socket_impl& impl_) noexcept : impl(impl_) {}
+
+    void do_cancel() noexcept override;
 };
 
 /** Accept operation state. */