FIX Avoid blocking WAV reads in realtime target (#2305)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 1c85c49c-2d6c-4050-b3e3-ce085c97c5ec

Author: romanlutz

pyrit/prompt_target/openai/openai_realtime_target.py

@@ -825,14 +825,7 @@ async def send_audio_async(
         """
         connection = self._get_connection(conversation_id=conversation_id)
 
-        with wave.open(filename, "rb") as wav_file:
-            # Read WAV parameters
-            num_channels = wav_file.getnchannels()
-            sample_width = wav_file.getsampwidth()  # Should be 2 bytes for PCM16
-            frame_rate = wav_file.getframerate()
-            num_frames = wav_file.getnframes()
-
-            audio_content = wav_file.readframes(num_frames)
+        audio_content, num_channels, sample_width, frame_rate = await asyncio.to_thread(self._read_wav_file, filename)
 
         receive_tasks = asyncio.create_task(self.receive_events_async(conversation_id=conversation_id))
 
@@ -871,3 +864,23 @@ async def _construct_message_from_response_async(self, response: Any, request: A
         This implementation exists to satisfy the abstract base class requirement.
         """
         raise NotImplementedError("RealtimeTarget uses receive_events for message construction")
+
+    @staticmethod
+    def _read_wav_file(filename: str) -> tuple[bytes, int, int, int]:
+        """
+        Read raw audio frames and format metadata from a WAV file.
+
+        Args:
+            filename (str): Path to the WAV file to read.
+
+        Returns:
+            tuple[bytes, int, int, int]: The raw audio frames, number of channels,
+                sample width in bytes, and frame rate.
+        """
+        with wave.open(filename, "rb") as wav_file:
+            return (
+                wav_file.readframes(wav_file.getnframes()),
+                wav_file.getnchannels(),
+                wav_file.getsampwidth(),
+                wav_file.getframerate(),
+            )

tests/unit/prompt_target/target/test_realtime_target.py

@@ -1216,6 +1216,36 @@ def _write_wav(
     return str(path)
 
 
+async def test_send_audio_async_reads_wav_off_event_loop(target, tmp_path):
+    connection = AsyncMock()
+    target._existing_conversation["conv"] = connection
+    target.receive_events_async = AsyncMock(
+        return_value=RealtimeTargetResult(audio_bytes=b"response", transcripts=["transcript"])
+    )
+    target.send_response_create_async = AsyncMock()
+    target.save_audio_async = AsyncMock(return_value="output.wav")
+
+    pcm = b"\x01\x02" * 8
+    wav_path = _write_wav(tmp_path / "input.wav", pcm=pcm)
+    with patch(
+        "pyrit.prompt_target.openai.openai_realtime_target.asyncio.to_thread",
+        new_callable=AsyncMock,
+        wraps=asyncio.to_thread,
+    ) as to_thread_mock:
+        output_path, _ = await target.send_audio_async(filename=wav_path, conversation_id="conv")
+
+    assert output_path == "output.wav"
+    assert to_thread_mock.await_args.args[1] == wav_path
+    connection.conversation.item.create.assert_awaited_once_with(
+        item={
+            "type": "message",
+            "role": "user",
+            "content": [{"type": "input_audio", "audio": base64.b64encode(pcm).decode("utf-8")}],
+        }
+    )
+    target.save_audio_async.assert_awaited_once_with(b"response", 1, 2, 24000)
+
+
 async def test_send_prompt_audio_path_calls_send_audio_async(target, tmp_path):
     """An audio_path message is routed through the atomic send_audio_async path."""
     wav_path = _write_wav(tmp_path / "in.wav")