78 lines
3.8 KiB
Python
78 lines
3.8 KiB
Python
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"""Regression test for #4729 — reasoning SSE coalescing throttle.
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The bug: during the reasoning/thinking phase of models like DeepSeek the server
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emitted one SSE `reasoning` event per token (tens of thousands per turn), each
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triggering a full-text scan in the frontend renderer and freezing the JS main thread.
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The fix throttles reasoning SSE events to ~10 Hz. The SUBTLE correctness requirement
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(the reason the first attempt was bounced): reasoning deltas are INCREMENTAL and the
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frontend APPENDS them (`reasoningText += text` in static/messages.js), so the throttle
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must COALESCE — accumulate dropped deltas into a buffer and flush the buffer, NOT drop
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deltas — otherwise live reasoning text is permanently lost. And the tail (the last
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sub-100ms window) must be flushed when the reasoning phase ends, or it's lost too.
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These are source-structure assertions on the on_reasoning closure in api/streaming.py
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(the closure isn't unit-testable in isolation), pinning the three properties so the
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coalescing contract can't silently regress to the drop-based version.
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"""
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import pathlib
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import re
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REPO = pathlib.Path(__file__).parent.parent
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STREAMING = (REPO / "api" / "streaming.py").read_text(encoding="utf-8")
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MESSAGES = (REPO / "static" / "messages.js").read_text(encoding="utf-8")
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def _on_reasoning_body() -> str:
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"""Extract the body of the on_reasoning closure by brace/indent scanning."""
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start = STREAMING.index("def on_reasoning(text):")
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# grab a generous slice (the closure is short) bounded by the next top-level
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# `def on_` callback in the same scope.
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nxt = STREAMING.find("\n def on_", start + 1)
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return STREAMING[start: nxt if nxt != -1 else start + 2500]
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def test_reasoning_uses_coalescing_buffer_not_drop():
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body = _on_reasoning_body()
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# A coalescing buffer accumulates every delta...
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assert "_reasoning_buffer[0] += reasoning_delta" in body, (
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"on_reasoning must ACCUMULATE each delta into the coalescing buffer — dropping "
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"deltas would permanently lose live reasoning text (the frontend appends them)"
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)
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# ...and the throttled flush emits the WHOLE buffer, then CLEARS it (so the next
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# emit carries only the since-last-flush accumulation — coarse delta, not cumulative).
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assert "put('reasoning', {'text': _reasoning_buffer[0]})" in body, (
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"the throttled flush must emit the accumulated buffer, not a single delta"
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)
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# the clear must follow the flush so we don't re-send already-delivered text
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flush_idx = body.index("put('reasoning', {'text': _reasoning_buffer[0]})")
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clear_idx = body.index("_reasoning_buffer[0] = ''", flush_idx)
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assert clear_idx > flush_idx, "the buffer must be cleared right after each flush"
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def test_reasoning_throttle_is_rate_limited():
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body = _on_reasoning_body()
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# ~10 Hz gate (0.1s) on the flush
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assert "_reasoning_last_put" in body and "0.1" in body, (
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"reasoning flush must be rate-limited to ~10 Hz (0.1s gate)"
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)
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def test_reasoning_tail_flushed_on_phase_end():
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body = _on_reasoning_body()
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# When the reasoning phase ends (text is None), any remaining buffered text must be
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# flushed so the last partial (<100ms) window isn't lost.
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none_branch = body[body.index("if text is None:"): body.index("if text is None:") + 400]
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assert "_reasoning_buffer[0]" in none_branch and "put('reasoning'" in none_branch, (
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"on_reasoning(text=None) must flush any remaining coalesced buffer (the tail)"
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)
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def test_frontend_appends_reasoning_deltas():
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# The whole coalesce requirement hinges on the frontend APPENDING (not replacing).
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# If this ever changes to assignment, the throttle design must change with it.
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assert "reasoningText += text" in MESSAGES, (
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"frontend reasoning handler must append deltas — if this changes, revisit the "
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"server-side coalescing throttle (#4729)"
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)
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