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fix(bedrock): emit contentBlockStart for all content block types in non-streaming mode #1849

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fix(bedrock): emit contentBlockStart for all content block types in non-streaming mode #1849

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27 changes: 23 additions & 4 deletions src/strands/models/bedrock.py
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Original file line number Diff line number Diff line change
Expand Up @@ -926,11 +926,14 @@ def _convert_non_streaming_to_streaming(self, response: dict[str, Any]) -> Itera
yield {"messageStart": {"role": response["output"]["message"]["role"]}}

# Process content blocks
for content in cast(list[ContentBlock], response["output"]["message"]["content"]):
# Yield contentBlockStart event if needed
for content_block_index, content in enumerate(
cast(list[ContentBlock], response["output"]["message"]["content"])
):
# Yield contentBlockStart for all content block types to match streaming behavior
if "toolUse" in content:
yield {
"contentBlockStart": {
"contentBlockIndex": content_block_index,
"start": {
"toolUse": {
"toolUseId": content["toolUse"]["toolUseId"],
Expand All @@ -945,14 +948,24 @@ def _convert_non_streaming_to_streaming(self, response: dict[str, Any]) -> Itera

yield {"contentBlockDelta": {"delta": {"toolUse": {"input": input_value}}}}
elif "text" in content:
# Then yield the text as a delta
yield {
"contentBlockStart": {
"contentBlockIndex": content_block_index,
"start": {},
}
}
yield {
"contentBlockDelta": {
"delta": {"text": content["text"]},
}
}
elif "reasoningContent" in content:
# Then yield the reasoning content as a delta
yield {
"contentBlockStart": {
"contentBlockIndex": content_block_index,
"start": {},
}
}
yield {
"contentBlockDelta": {
"delta": {"reasoningContent": {"text": content["reasoningContent"]["reasoningText"]["text"]}}
Expand All @@ -970,6 +983,12 @@ def _convert_non_streaming_to_streaming(self, response: dict[str, Any]) -> Itera
}
}
elif "citationsContent" in content:
yield {
"contentBlockStart": {
"contentBlockIndex": content_block_index,
"start": {},
}
}
# For non-streaming citations, emit text and metadata deltas in sequence
# to match streaming behavior where they flow naturally
if "content" in content["citationsContent"]:
Expand Down
14 changes: 13 additions & 1 deletion tests/strands/models/test_bedrock.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1092,6 +1092,7 @@ async def test_stream_with_streaming_false(bedrock_client, alist, messages):
tru_events = await alist(response)
exp_events = [
{"messageStart": {"role": "assistant"}},
{"contentBlockStart": {"contentBlockIndex": 0, "start": {}}},
{"contentBlockDelta": {"delta": {"text": "test"}}},
{"contentBlockStop": {}},
{"messageStop": {"stopReason": "end_turn", "additionalModelResponseFields": None}},
Expand Down Expand Up @@ -1122,7 +1123,12 @@ async def test_stream_with_streaming_false_and_tool_use(bedrock_client, alist, m
tru_events = await alist(response)
exp_events = [
{"messageStart": {"role": "assistant"}},
{"contentBlockStart": {"start": {"toolUse": {"toolUseId": "123", "name": "dummyTool"}}}},
{
"contentBlockStart": {
"contentBlockIndex": 0,
"start": {"toolUse": {"toolUseId": "123", "name": "dummyTool"}},
}
},
{"contentBlockDelta": {"delta": {"toolUse": {"input": '{"hello": "world!"}'}}}},
{"contentBlockStop": {}},
{"messageStop": {"stopReason": "tool_use", "additionalModelResponseFields": None}},
Expand Down Expand Up @@ -1159,6 +1165,7 @@ async def test_stream_with_streaming_false_and_reasoning(bedrock_client, alist,
tru_events = await alist(response)
exp_events = [
{"messageStart": {"role": "assistant"}},
{"contentBlockStart": {"contentBlockIndex": 0, "start": {}}},
{"contentBlockDelta": {"delta": {"reasoningContent": {"text": "Thinking really hard...."}}}},
{"contentBlockDelta": {"delta": {"reasoningContent": {"signature": "123"}}}},
{"contentBlockStop": {}},
Expand Down Expand Up @@ -1197,6 +1204,7 @@ async def test_stream_and_reasoning_no_signature(bedrock_client, alist, messages
tru_events = await alist(response)
exp_events = [
{"messageStart": {"role": "assistant"}},
{"contentBlockStart": {"contentBlockIndex": 0, "start": {}}},
{"contentBlockDelta": {"delta": {"reasoningContent": {"text": "Thinking really hard...."}}}},
{"contentBlockStop": {}},
{"messageStop": {"stopReason": "tool_use", "additionalModelResponseFields": None}},
Expand Down Expand Up @@ -1224,6 +1232,7 @@ async def test_stream_with_streaming_false_with_metrics_and_usage(bedrock_client
tru_events = await alist(response)
exp_events = [
{"messageStart": {"role": "assistant"}},
{"contentBlockStart": {"contentBlockIndex": 0, "start": {}}},
{"contentBlockDelta": {"delta": {"text": "test"}}},
{"contentBlockStop": {}},
{"messageStop": {"stopReason": "tool_use", "additionalModelResponseFields": None}},
Expand Down Expand Up @@ -1265,6 +1274,7 @@ async def test_stream_input_guardrails(bedrock_client, alist, messages):
tru_events = await alist(response)
exp_events = [
{"messageStart": {"role": "assistant"}},
{"contentBlockStart": {"contentBlockIndex": 0, "start": {}}},
{"contentBlockDelta": {"delta": {"text": "test"}}},
{"contentBlockStop": {}},
{"messageStop": {"stopReason": "end_turn", "additionalModelResponseFields": None}},
Expand Down Expand Up @@ -1316,6 +1326,7 @@ async def test_stream_output_guardrails(bedrock_client, alist, messages):
tru_events = await alist(response)
exp_events = [
{"messageStart": {"role": "assistant"}},
{"contentBlockStart": {"contentBlockIndex": 0, "start": {}}},
{"contentBlockDelta": {"delta": {"text": "test"}}},
{"contentBlockStop": {}},
{"messageStop": {"stopReason": "end_turn", "additionalModelResponseFields": None}},
Expand Down Expand Up @@ -1369,6 +1380,7 @@ async def test_stream_output_guardrails_redacts_output(bedrock_client, alist, me
tru_events = await alist(response)
exp_events = [
{"messageStart": {"role": "assistant"}},
{"contentBlockStart": {"contentBlockIndex": 0, "start": {}}},
{"contentBlockDelta": {"delta": {"text": "test"}}},
{"contentBlockStop": {}},
{"messageStop": {"stopReason": "end_turn", "additionalModelResponseFields": None}},
Expand Down