tests: run the half-close case on Windows again

The previous commit lets a half-closed client be written to on Windows
too, so the case left out there is back.

This reverts commit 5d1cdf8.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/cases/portmap.py

@@ -1,7 +1,6 @@
 """The port mappers: tcppm forwards a TCP port, udppm a UDP one."""
 
 import socket
-import sys
 import threading
 import time
 
@@ -65,44 +64,38 @@ def run(t):
 
     t.stop_all()
 
-    # WSAPoll reports a hang-up once the peer has half-closed, not once
-    # both sides are shut down as poll() does elsewhere, and sockmap() takes
-    # it for a client it can no longer write to: not covered there yet.
-    if sys.platform == "win32":
-        t.skip("a half-closed client gets the whole answer (not on Windows)")
-    else:
-        # A client which shuts down its sending side still gets the whole answer,
-        # even when it reads slowly: the server has finished and closed by then,
-        # and the rest of the answer waits in the proxy's buffer and the kernel's.
-        listener = socket.socket()
-        listener.bind(("127.0.0.1", 0))
-        listener.listen(1)
-        threading.Thread(target=halfclose_origin, args=(listener,), daemon=True).start()
-        halfclosed = t.free_port()
-        t.start("portmap_halfclose", f"""
-            log
-            auth none
-            tcppm {halfclosed} 127.0.0.1 {listener.getsockname()[1]}
-        """, ports=[halfclosed])
-        s = socket.socket()
-        s.setsockopt(socket.SOL_SOCKET, socket.SO_RCVBUF, 32768)
-        s.settimeout(30)
-        got = 0
-        try:
-            s.connect(("127.0.0.1", halfclosed))
-            s.sendall(b"request")
-            s.shutdown(socket.SHUT_WR)
-            time.sleep(1)
-            while True:
-                d = s.recv(65536)
-                if not d:
-                    break
-                got += len(d)
-        except OSError:
-            pass
-        s.close()
-        listener.close()
-        t.eq(HALFCLOSE_SIZE, got, "a half-closed client reading slowly gets the whole answer")
+    # A client which shuts down its sending side still gets the whole answer,
+    # even when it reads slowly: the server has finished and closed by then,
+    # and the rest of the answer waits in the proxy's buffer and the kernel's.
+    listener = socket.socket()
+    listener.bind(("127.0.0.1", 0))
+    listener.listen(1)
+    threading.Thread(target=halfclose_origin, args=(listener,), daemon=True).start()
+    halfclosed = t.free_port()
+    t.start("portmap_halfclose", f"""
+        log
+        auth none
+        tcppm {halfclosed} 127.0.0.1 {listener.getsockname()[1]}
+    """, ports=[halfclosed])
+    s = socket.socket()
+    s.setsockopt(socket.SOL_SOCKET, socket.SO_RCVBUF, 32768)
+    s.settimeout(30)
+    got = 0
+    try:
+        s.connect(("127.0.0.1", halfclosed))
+        s.sendall(b"request")
+        s.shutdown(socket.SHUT_WR)
+        time.sleep(1)
+        while True:
+            d = s.recv(65536)
+            if not d:
+                break
+            got += len(d)
+    except OSError:
+        pass
+    s.close()
+    listener.close()
+    t.eq(HALFCLOSE_SIZE, got, "a half-closed client reading slowly gets the whole answer")
 
     t.stop_all()