fix: check cancel signal inside aiter_bytes() loop and clarify docstrings

Author: liramon2

strands-py/src/strands/vended_tools/web_fetch/web_fetch.py

@@ -64,8 +64,8 @@ def make_web_fetch(
             5 MiB.
         client: Optional ``httpx.AsyncClient`` to use for requests. When
             provided, the tool uses it directly and will not close it.
-            When ``None``, a new client is created per request with httpx
-            defaults.
+            When ``None``, a new client is created per request with
+            ``follow_redirects=True`` and httpx's default timeout (5s).
         model: Optional model for the summarizer. Resolution order when
             ``prompt`` is non-empty: this model, then the host agent's model,
             then ``ValueError`` if neither is available.
@@ -88,8 +88,7 @@ async def web_fetch_tool(
         """Fetches an HTTP(S) URL and returns readable content.
 
         Only ``http://`` and ``https://`` URLs are accepted. Raises
-        ``TimeoutError`` if the request does not complete within the
-        configured timeout.
+        ``TimeoutError`` if the request exceeds the client's timeout.
 
         Args:
             url: The URL to fetch. Must be ``http://`` or ``https://``.
@@ -125,8 +124,7 @@ async def web_fetch_tool(
             effective_model = summarizer_model or getattr(agent_obj, "model", None)
             if effective_model is None:
                 raise ValueError(
-                    "web_fetch: prompt requires a model. Pass model= to make_web_fetch "
-                    "or call the tool from an agent."
+                    "web_fetch: prompt requires a model. Pass model= to make_web_fetch or call the tool from an agent."
                 )
             # Fresh agent per call — no history from one fetch bleeds into the next.
             summarizer = Agent(
@@ -180,6 +178,7 @@ async def _fetch_once(
             chunks: list[bytes] = []
             total = 0
             async for chunk in response.aiter_bytes():
+                _check_cancelled(cancel_signal)
                 total += len(chunk)
                 if total > max_bytes:
                     raise ValueError(f"Response body exceeded {max_bytes} bytes. Refusing to buffer more.")

strands-py/tests/strands/vended_tools/test_web_fetch.py

@@ -208,6 +208,28 @@ def handler(_request: httpx.Request) -> httpx.Response:
         with pytest.raises(asyncio.CancelledError):
             await tool(url="https://example.com/", tool_context=ctx)
 
+    @pytest.mark.asyncio
+    async def test_mid_flight_cancel_aborts_between_chunks(self):
+        cancel = threading.Event()
+
+        def handler(_request: httpx.Request) -> httpx.Response:
+            async def body():
+                yield b"chunk-one"
+                cancel.set()  # signal mid-stream
+                yield b"chunk-two"
+
+            return httpx.Response(200, headers={"content-type": "text/plain"}, content=body())
+
+        agent = SimpleNamespace(_cancel_signal=cancel)
+        from strands.types.tools import ToolContext, ToolUse
+
+        tool_use = ToolUse(toolUseId="wf_2", name="web_fetch", input={})
+        ctx = ToolContext(tool_use=tool_use, agent=agent, invocation_state={})
+
+        tool = make_web_fetch(client=_client(handler))
+        with pytest.raises(asyncio.CancelledError):
+            await tool(url="https://example.com/", tool_context=ctx)
+
 
 class TestSummarizer:
     """Summarizer agent is called when model + prompt are both provided."""