gh-142403: Avoid leaking file descriptor in socket.py

Author: AZero13

Lib/socket.py

@@ -376,45 +376,46 @@ def _sendfile_zerocopy(self, zerocopy_func, giveup_exc_type, file,
         # poll/select have the advantage of not requiring any
         # extra file descriptor, contrarily to epoll/kqueue
         # (also, they require a single syscall).
-        if hasattr(selectors, 'PollSelector'):
-            selector = selectors.PollSelector()
-        else:
-            selector = selectors.SelectSelector()
-        selector.register(sockno, selectors.EVENT_WRITE)
-
         total_sent = 0
-        # localize variable access to minimize overhead
-        selector_select = selector.select
         try:
-            while True:
-                if timeout and not selector_select(timeout):
-                    raise TimeoutError('timed out')
-                if count:
-                    blocksize = min(count - total_sent, blocksize)
-                    if blocksize <= 0:
-                        break
-                try:
-                    sent = zerocopy_func(fileno, offset, blocksize)
-                except BlockingIOError:
-                    if not timeout:
-                        # Block until the socket is ready to send some
-                        # data; avoids hogging CPU resources.
-                        selector_select()
-                    continue
-                except OSError as err:
-                    if total_sent == 0:
-                        # We can get here for different reasons, the main
-                        # one being 'file' is not a regular mmap(2)-like
-                        # file, in which case we'll fall back on using
-                        # plain send().
-                        raise giveup_exc_type(err)
-                    raise err from None
-                else:
-                    if sent == 0:
-                        break  # EOF
-                    offset += sent
-                    total_sent += sent
-            return total_sent
+            with (
+                selectors.PollSelector()
+                if hasattr(selectors, 'PollSelector')
+                else selectors.SelectSelector()
+            ) as selector:
+                selector.register(sockno, selectors.EVENT_WRITE)
+
+                # localize variable access to minimize overhead
+                selector_select = selector.select
+                while True:
+                    if timeout and not selector_select(timeout):
+                        raise TimeoutError('timed out')
+                    if count:
+                        blocksize = min(count - total_sent, blocksize)
+                        if blocksize <= 0:
+                            break
+                    try:
+                        sent = zerocopy_func(fileno, offset, blocksize)
+                    except BlockingIOError:
+                        if not timeout:
+                            # Block until the socket is ready to send some
+                            # data; avoids hogging CPU resources.
+                            selector_select()
+                        continue
+                    except OSError as err:
+                        if total_sent == 0:
+                            # We can get here for different reasons, the main
+                            # one being 'file' is not a regular mmap(2)-like
+                            # file, in which case we'll fall back on using
+                            # plain send().
+                            raise giveup_exc_type(err)
+                        raise err from None
+                    else:
+                        if sent == 0:
+                            break  # EOF
+                        offset += sent
+                        total_sent += sent
+                return total_sent
         finally:
             if total_sent > 0 and hasattr(file, 'seek'):
                 file.seek(offset)

Misc/NEWS.d/next/Library/2025-12-10-09-16-46.gh-issue-142403.MCyTuL.rst

@@ -0,0 +1 @@
+Stop leaking the selector file descriptor, and release it when done.