[HttpClient] doc how to cancel a request

Author: nicolas-grekas

components/http_client.rst

@@ -303,6 +303,29 @@ response sequentially instead of waiting for the entire response::
         fwrite($fileHandler, $chunk->getContent());
     }
 
+Canceling Responses
+~~~~~~~~~~~~~~~~~~~
+
+To abort a request (e.g. because it didn't answer in due time, or you want to
+fetch only the first bytes of the response, etc.), you can either:
+
+* use the ``cancel()`` method of ``ResponseInterface``::
+
+      $response->cancel()
+
+* throw an exception from a progress callback::
+
+      $response = $client->request('GET', 'https://..;', [
+        'on_progress' => function (int $dlNow, int $dlSize, array $info): void {
+            // ...
+
+            throw new \MyException();
+        },
+      ]);
+
+  The exception will be wrapped in a ``TransportExceptionInterface`` and will
+  abort the request.
+
 Handling Exceptions
 ~~~~~~~~~~~~~~~~~~~