Foundation: correct handle management on URLSession

We would cast the CURL socket type to an Int and back during the
MultiHandle setup.  This does not work properly for Windows.  Given that
the interfaces are internal, keep the type sugar as far as possible
before handing off to libdispatch.

Author: compnerd

Foundation/URLSession/libcurl/MultiHandle.swift

@@ -122,7 +122,7 @@ fileprivate extension URLSession._MultiHandle {
             let handler = DispatchWorkItem { [weak self] in
                 self?.performAction(for: socket)
             }
-            ss.createSources(with: action, fileDescriptor: Int(socket), queue: queue, handler: handler)
+            ss.createSources(with: action, socket: socket, queue: queue, handler: handler)
         }
         return 0
     }
@@ -395,17 +395,25 @@ fileprivate class _SocketSources {
     var readSource: DispatchSource?
     var writeSource: DispatchSource?
 
-    func createReadSource(fileDescriptor fd: Int, queue: DispatchQueue, handler: DispatchWorkItem) {
+    func createReadSource(socket: CFURLSession_socket_t, queue: DispatchQueue, handler: DispatchWorkItem) {
         guard readSource == nil else { return }
-        let s = DispatchSource.makeReadSource(fileDescriptor: Int32(fd), queue: queue)
+#if os(Windows)
+        let s = DispatchSource.makeReadSource(handle: HANDLE(bitPattern: Int(socket))!, queue: queue)
+#else
+        let s = DispatchSource.makeReadSource(fileDescriptor: socket, queue: queue)
+#endif
         s.setEventHandler(handler: handler)
         readSource = s as? DispatchSource
         s.resume()
     }
 
-    func createWriteSource(fileDescriptor fd: Int, queue: DispatchQueue, handler: DispatchWorkItem) {
+    func createWriteSource(socket: CFURLSession_socket_t, queue: DispatchQueue, handler: DispatchWorkItem) {
         guard writeSource == nil else { return }
-        let s = DispatchSource.makeWriteSource(fileDescriptor: Int32(fd), queue: queue)
+#if os(Windows)
+        let s = DispatchSource.makeWriteSource(handle: HANDLE(bitPattern: Int(socket))!, queue: queue)
+#else
+        let s = DispatchSource.makeWriteSource(fileDescriptor: socket, queue: queue)
+#endif
         s.setEventHandler(handler: handler)
         writeSource = s as? DispatchSource
         s.resume()
@@ -424,12 +432,12 @@ fileprivate class _SocketSources {
 }
 extension _SocketSources {
     /// Create a read and/or write source as specified by the action.
-    func createSources(with action: URLSession._MultiHandle._SocketRegisterAction, fileDescriptor fd: Int, queue: DispatchQueue, handler: DispatchWorkItem) {
+    func createSources(with action: URLSession._MultiHandle._SocketRegisterAction, socket: CFURLSession_socket_t, queue: DispatchQueue, handler: DispatchWorkItem) {
         if action.needsReadSource {
-            createReadSource(fileDescriptor: fd, queue: queue, handler: handler)
+            createReadSource(socket: socket, queue: queue, handler: handler)
         }
         if action.needsWriteSource {
-            createWriteSource(fileDescriptor: fd, queue: queue, handler: handler)
+            createWriteSource(socket: socket, queue: queue, handler: handler)
         }
     }
 }