Raise exception for shutdown on a connection already released to the pool (#3601)

Co-authored-by: Quentin Pradet <[email protected]>

Author: alexprabhat99

changelog/3581.bugfix.rst

@@ -0,0 +1 @@
+Raise exception for HTTPResponse.shutdown on a connection already released to the pool.

src/urllib3/response.py

@@ -1100,6 +1100,10 @@ def readable(self) -> bool:
     def shutdown(self) -> None:
         if not self._sock_shutdown:
             raise ValueError("Cannot shutdown socket as self._sock_shutdown is not set")
+        if self._connection is None:
+            raise RuntimeError(
+                "Cannot shutdown as connection has already been released to the pool"
+            )
         self._sock_shutdown(socket.SHUT_RD)
 
     def close(self) -> None:

test/with_dummyserver/test_connectionpool.py

@@ -912,6 +912,18 @@ def test_cleanup_on_connection_error(self) -> None:
             # the pool should still contain poolsize elements
             assert http.pool.qsize() == http.pool.maxsize
 
+    def test_shutdown_on_connection_released_to_pool(self) -> None:
+        with HTTPConnectionPool(self.host, self.port) as pool:
+            resp = pool.urlopen("GET", "/", preload_content=False)
+            resp.drain_conn()
+            resp.release_conn()
+
+        with pytest.raises(
+            RuntimeError,
+            match="Cannot shutdown as connection has already been released to the pool",
+        ):
+            resp.shutdown()
+
     def test_mixed_case_hostname(self) -> None:
         with HTTPConnectionPool("LoCaLhOsT", self.port) as pool:
             response = pool.request("GET", f"http://LoCaLhOsT:{self.port}/")