fix: Truncate MCP http debug logs if greater than 1000 chars

To prevent OOM issues if HTTP request/response bodies are too long

Co-authored-by: Kathy Wu <wukathy@google.com>
PiperOrigin-RevId: 943502772

Author: wukath

src/google/adk/tools/mcp_tool/mcp_session_manager.py

@@ -81,6 +81,8 @@ class AsyncAuthorizedSession:  # pylint: disable=g-bad-classes
 
 logger = logging.getLogger('google_adk.' + __name__)
 
+_MAX_LOG_BODY_LENGTH = 1000
+
 
 def create_mcp_http_client(
     headers: dict[str, str] | None = None,
@@ -271,13 +273,19 @@ async def _response_hook(self, response: httpx.Response):
         request_body = response.request.content.decode(
             'utf-8', errors='replace'
         )
+        if len(request_body) > _MAX_LOG_BODY_LENGTH:
+          request_body = request_body[:_MAX_LOG_BODY_LENGTH] + '... [truncated]'
       except Exception:  # pylint: disable=broad-exception-caught
         request_body = '<binary>'
 
     if not is_sse:
       try:
         await response.aread()
         response_body = response.text
+        if len(response_body) > _MAX_LOG_BODY_LENGTH:
+          response_body = (
+              response_body[:_MAX_LOG_BODY_LENGTH] + '... [truncated]'
+          )
       except Exception as e:  # pylint: disable=broad-exception-caught
         response_body = f'<failed to read body: {e}>'
     else:

tests/unittests/tools/mcp_tool/test_mcp_session_manager.py

@@ -1471,3 +1471,46 @@ def keyword_only_factory(**kwargs) -> httpx.AsyncClient:
     client = debug_factory({"X-Test": "Val"}, None, None)
     assert client is base_client
     await base_client.aclose()
+
+  @pytest.mark.asyncio
+  async def test_response_hook_truncates_large_bodies(self):
+    """Test that response hook truncates request and response bodies exceeding limit."""
+    base_client = httpx.AsyncClient()
+    base_factory = Mock(return_value=base_client)
+    debug_factory = _DebugHttpxClientFactory(base_factory)
+
+    # Mock request and response with large content
+    large_req_body = b"a" * 1500
+    large_resp_body = "b" * 1500
+
+    mock_request = Mock(spec=httpx.Request)
+    mock_request.method = "POST"
+    mock_request.content = large_req_body
+    mock_request.headers = httpx.Headers()
+
+    mock_response = Mock(spec=httpx.Response)
+    mock_response.url = httpx.URL("https://example.com/large")
+    mock_response.status_code = 200
+    mock_response.request = mock_request
+    mock_response.headers = httpx.Headers({"content-type": "application/json"})
+    mock_response.text = large_resp_body
+    mock_response.aread = AsyncMock()
+
+    debug_list = []
+    token = _http_debug_var.set(debug_list)
+    try:
+      await debug_factory._response_hook(mock_response)
+    finally:
+      _http_debug_var.reset(token)
+
+    assert len(debug_list) == 1
+    record = debug_list[0]
+    assert len(record["request_body"]) == 1015  # 1000 + len("... [truncated]")
+    assert record["request_body"].endswith("... [truncated]")
+    assert record["request_body"].startswith("a" * 1000)
+
+    assert len(record["response_body"]) == 1015  # 1000 + len("... [truncated]")
+    assert record["response_body"].endswith("... [truncated]")
+    assert record["response_body"].startswith("b" * 1000)
+
+    await base_client.aclose()