Skip to content

fix: emit ToolUseStreamEvent on contentBlockStart for thinking-phase tool calls #1569

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
a-sekka wants to merge 1 commit into
base: main
Choose a base branch
from
+52 −3
Open

fix: emit ToolUseStreamEvent on contentBlockStart for thinking-phase tool calls #1569

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
5 changes: 5 additions & 0 deletions src/strands/event_loop/streaming.py
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -400,6 +400,11 @@ async def process_stream(
state["message"] = handle_message_start(chunk["messageStart"], state["message"])
elif "contentBlockStart" in chunk:
state["current_tool_use"] = handle_content_block_start(chunk["contentBlockStart"])
if state["current_tool_use"]:
yield ToolUseStreamEvent(
delta={"toolUse": {"input": ""}},
current_tool_use=state["current_tool_use"],
)
elif "contentBlockDelta" in chunk:
state, typed_event = handle_content_block_delta(chunk["contentBlockDelta"], state)
yield typed_event
Expand Down
50 changes: 47 additions & 3 deletions tests/strands/event_loop/test_streaming.py
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -603,6 +603,19 @@ def test_extract_usage_metrics_empty_metadata():
},
},
},
{
"current_tool_use": {
"input": {"key": "value"},
"name": "test",
"toolUseId": "123",
},
"delta": {
"toolUse": {
"input": "",
},
},
"type": "tool_use_stream",
},
{
"event": {
"contentBlockDelta": {
Expand All @@ -616,9 +629,7 @@ def test_extract_usage_metrics_empty_metadata():
},
{
"current_tool_use": {
"input": {
"key": "value",
},
"input": {"key": "value"},
"name": "test",
"toolUseId": "123",
},
Expand Down Expand Up @@ -1257,6 +1268,39 @@ async def test_stream_messages_none_system_prompt_content(agenerator, alist):
assert non_typed_events == []


@pytest.mark.asyncio
async def test_process_stream_emits_tool_use_event_on_content_block_start(agenerator, alist):
"""Test that a ToolUseStreamEvent is emitted on contentBlockStart with toolUse.

This ensures tool calls are visible to users even when executed during the model's
thinking/reasoning phase before any contentBlockDelta events are received.
See: https://github.com/strands-agents/sdk-python/issues/1551
"""
response = [
{"messageStart": {"role": "assistant"}},
{
"contentBlockStart": {"start": {"toolUse": {"toolUseId": "tool-1", "name": "get_user_info"}}},
},
{"contentBlockStop": {}},
{"messageStop": {"stopReason": "tool_use"}},
{
"metadata": {
"usage": {"inputTokens": 1, "outputTokens": 1, "totalTokens": 1},
"metrics": {"latencyMs": 1},
}
},
]

stream = strands.event_loop.streaming.process_stream(agenerator(response))
events = await alist(stream)

# Find the ToolUseStreamEvent - should be emitted right after contentBlockStart
tool_use_events = [e for e in events if e.get("type") == "tool_use_stream"]
assert len(tool_use_events) == 1
assert tool_use_events[0]["current_tool_use"]["name"] == "get_user_info"
assert tool_use_events[0]["current_tool_use"]["toolUseId"] == "tool-1"


@pytest.mark.asyncio
async def test_stream_messages_normalizes_messages(agenerator, alist):
mock_model = unittest.mock.MagicMock()
Expand Down