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fix(translation): reject incomplete anthropic streams #283

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fix(translation): reject incomplete anthropic streams #283

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36 changes: 36 additions & 0 deletions crates/switchyard-translation/src/helpers.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -196,6 +196,7 @@ where
source: Some(source_format.clone()),
..StreamTranslationState::default()
};
let mut saw_anthropic_message_stop = false;
let mut frame = String::new();
let stream = Box::pin(try_stream! {
futures::pin_mut!(lines);
Expand All @@ -210,6 +211,8 @@ where
sse::SseFrame::Empty => {}
sse::SseFrame::Done => break,
sse::SseFrame::Data(value) => {
saw_anthropic_message_stop |= source == WireFormat::AnthropicMessages
&& value.get("type").and_then(Value::as_str) == Some("message_stop");
let normalized = codec.decode_event(&mut state, &value);
yield LlmResponseStreamEvent::preserved(
source_format.clone(),
Expand All @@ -231,10 +234,18 @@ where
let parsed = sse::parse_json_sse_frame(&frame, marker)
.map_err(|error| LlmClientError::ResponseTranslation(error.to_string()))?;
if let sse::SseFrame::Data(value) = parsed {
saw_anthropic_message_stop |= source == WireFormat::AnthropicMessages
&& value.get("type").and_then(Value::as_str) == Some("message_stop");
let normalized = codec.decode_event(&mut state, &value);
yield LlmResponseStreamEvent::preserved(source_format, value, normalized);
}
}

if source == WireFormat::AnthropicMessages && !saw_anthropic_message_stop {

@nachiketb-nvidia nachiketb-nvidia Aug 4, 2026

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Could we treat Anthropic error events as terminal too? Otherwise EOF emits a second misleading ended before message_stop error after the upstream error.

Err(LlmClientError::ResponseTranslation(
"anthropic stream ended before message_stop".to_string(),
))?;
}
});
Ok(stream)
}
Expand Down Expand Up @@ -570,6 +581,31 @@ mod tests {
Ok(())
}

#[test]
fn anthropic_stream_without_message_stop_is_an_error() -> Result<(), BoxError> {
let sse = b"event: message_start\ndata: {\"type\":\"message_start\",\"message\":{\"id\":\"msg_1\",\"model\":\"claude\"}}\n\n".to_vec();
let bytes = stream::once(async move { Ok::<Vec<u8>, LlmClientError>(sse) });
let decoded = decode_stream(bytes, WireFormat::AnthropicMessages)?;
let results = block_on(
encode_stream(decoded, WireFormat::AnthropicMessages, None)?.collect::<Vec<_>>(),
);

let Some(Err(error)) = results.last() else {
panic!("expected incomplete Anthropic stream to fail");
};
assert_eq!(
error.to_string(),
"response translation failed: anthropic stream ended before message_stop"
);
assert!(
results
.iter()
.filter_map(|result| result.as_ref().ok())
.all(|event| event.get("type").and_then(Value::as_str) != Some("message_stop"))
);
Ok(())
}

#[test]
fn decode_stream_decodes_crlf_delimited_frames() -> Result<(), BoxError> {
// CRLF framing: blank lines are `\r\n\r\n` and the bare `\r` must not
Expand Down
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