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[world-vercel] Use stream close control frame to decide whether to reconnect to stream - #1742
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# Conflicts: # packages/world-vercel/src/streamer.test.ts # packages/world-vercel/src/streamer.ts
🦋 Changeset detectedLatest commit: 552c2eb The changes in this PR will be included in the next version bump. This PR includes changesets to release 18 packages
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🧪 E2E Test Results❌ Some tests failed Summary
❌ Failed Tests🌍 Community Worlds (74 failed)mongodb (7 failed):
redis (7 failed):
turso (60 failed):
Details by Category✅ ▲ Vercel Production
✅ 💻 Local Development
✅ 📦 Local Production
✅ 🐘 Local Postgres
✅ 🪟 Windows
❌ 🌍 Community Worlds
✅ 📋 Other
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📊 Benchmark Results
workflow with no steps💻 Local Development
▲ Production (Vercel)
🔍 Observability: Nitro | Next.js (Turbopack) workflow with 1 step💻 Local Development
▲ Production (Vercel)
🔍 Observability: Nitro | Next.js (Turbopack) workflow with 10 sequential steps💻 Local Development
▲ Production (Vercel)
🔍 Observability: Nitro | Next.js (Turbopack) workflow with 25 sequential steps💻 Local Development
▲ Production (Vercel)
🔍 Observability: Nitro | Next.js (Turbopack) workflow with 50 sequential steps💻 Local Development
▲ Production (Vercel)
🔍 Observability: Nitro | Next.js (Turbopack) Promise.all with 10 concurrent steps💻 Local Development
▲ Production (Vercel)
🔍 Observability: Nitro | Next.js (Turbopack) Promise.all with 25 concurrent steps💻 Local Development
▲ Production (Vercel)
🔍 Observability: Next.js (Turbopack) | Nitro Promise.all with 50 concurrent steps💻 Local Development
▲ Production (Vercel)
🔍 Observability: Nitro | Next.js (Turbopack) Promise.race with 10 concurrent steps💻 Local Development
▲ Production (Vercel)
🔍 Observability: Next.js (Turbopack) | Nitro Promise.race with 25 concurrent steps💻 Local Development
▲ Production (Vercel)
🔍 Observability: Next.js (Turbopack) | Nitro Promise.race with 50 concurrent steps💻 Local Development
▲ Production (Vercel)
🔍 Observability: Nitro | Next.js (Turbopack) workflow with 10 sequential data payload steps (10KB)💻 Local Development
▲ Production (Vercel)
🔍 Observability: Nitro | Next.js (Turbopack) workflow with 25 sequential data payload steps (10KB)💻 Local Development
▲ Production (Vercel)
🔍 Observability: Nitro | Next.js (Turbopack) workflow with 50 sequential data payload steps (10KB)💻 Local Development
▲ Production (Vercel)
🔍 Observability: Nitro | Next.js (Turbopack) workflow with 10 concurrent data payload steps (10KB)💻 Local Development
▲ Production (Vercel)
🔍 Observability: Nitro | Next.js (Turbopack) workflow with 25 concurrent data payload steps (10KB)💻 Local Development
▲ Production (Vercel)
🔍 Observability: Nitro | Next.js (Turbopack) workflow with 50 concurrent data payload steps (10KB)💻 Local Development
▲ Production (Vercel)
🔍 Observability: Nitro | Next.js (Turbopack) Stream Benchmarks(includes TTFB metrics)workflow with stream💻 Local Development
▲ Production (Vercel)
🔍 Observability: Nitro | Next.js (Turbopack) stream pipeline with 5 transform steps (1MB)💻 Local Development
▲ Production (Vercel)
🔍 Observability: Nitro | Next.js (Turbopack) 10 parallel streams (1MB each)💻 Local Development
▲ Production (Vercel)
🔍 Observability: Nitro | Next.js (Turbopack) fan-out fan-in 10 streams (1MB each)💻 Local Development
▲ Production (Vercel)
🔍 Observability: Nitro | Next.js (Turbopack) SummaryFastest Framework by WorldWinner determined by most benchmark wins
Fastest World by FrameworkWinner determined by most benchmark wins
Column Definitions
Worlds:
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- Fix streamer-reconnect.test.ts: use streams.get(runId, name) instead of non-existent readFromStream method - Update stream GET URL from v2 to v3 to receive control frames - Remove unused readFromStream from Streamer interface - Reset WORKFLOW_SERVER_URL_OVERRIDE to empty string Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Signed-off-by: Peter Wielander <mittgfu@gmail.com>
| */ | ||
| const WORKFLOW_SERVER_URL_OVERRIDE = ''; | ||
| const WORKFLOW_SERVER_URL_OVERRIDE = | ||
| 'https://workflow-server-git-peter-stream-control-frame.vercel.sh'; |
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Don't forget to remove this before merging
TooTallNate
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Apr 16, 2026
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The reconnection design is well thought out. The hold-back buffer approach for control frame detection is correct and handles all edge cases I traced through (split frames, coalesced chunks, empty streams, short data). The test coverage is thorough. But there's one blocking issue and a couple of concerns.
Backend compatibility note: The backend currently only emits the trailing control frame when a stream closes due to the server-side timeout — a naturally-completed stream closes without a frame. This client correctly handles that via the "no control frame" fallback path, so the two sides are compatible as-is. However, the backend change this depends on is still in review; this PR should not be merged until that is resolved and deployed.
Changes reviewed:
parseStreamControlFrame(streamer.ts): Correct implementation of the documented wire format. Checks zero-marker + magic footer, parses flags and nextIndex.- Hold-back buffer (
streamer.ts:278-348): Retains last 13 bytes during streaming to detect the control frame at close. Handles split frames, coalesced chunks, and backward compat (no frame) gracefully. - Reconnection loop (
streamer.ts:335-345): Ondone=false, reconnects fromcontrol.nextIndex. Clean loop. - Error handling (
streamer.ts:289-296): Network errors flush the buffer and close without retrying. Correct. - Unit tests (
streamer.test.ts): Good coverage ofparseStreamControlFrameedge cases. - Integration tests (
streamer-reconnect.test.ts): Comprehensive — covers single reconnect, multiple reconnects, split frames, coalesced frames, empty streams, backwards compat, network errors, and non-200 responses.
| */ | ||
| const WORKFLOW_SERVER_URL_OVERRIDE = ''; | ||
| const WORKFLOW_SERVER_URL_OVERRIDE = | ||
| 'https://workflow-server-git-peter-stream-control-frame.vercel.sh'; |
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Blocking: This hardcodes WORKFLOW_SERVER_URL_OVERRIDE to a preview deployment URL. This must be reverted to '' before merging — it would route all production traffic to a preview branch deployment.
(I left a comment about this earlier, flagging again as blocking since it's still present.)
| controller.enqueue(tailBuffer); | ||
| tailBuffer = new Uint8Array(0); | ||
| } | ||
| controller.close(); |
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Non-blocking concern: On network error, the code swallows the error and calls controller.close() instead of controller.error(err). This means consumers of the returned ReadableStream see a clean close rather than an error, and have no way to know the stream was truncated.
The reconnect test asserts the partial data is received and only 1 fetch is made, which is correct for "no retry on errors." But silently closing on error could be a footgun — the consumer (the workflow VM) would think it received the complete stream.
Consider either:
- Propagating the error via
controller.error(err)so consumers can handle it - Or at minimum, logging a warning
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Fixed in 6ee6e7d — network errors now propagate via controller.error(err) instead of silently closing.
| } | ||
| const response = await fetch(url, { | ||
| headers: httpConfig.headers, | ||
| let currentStartIndex = startIndex ?? 0; |
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Non-blocking: There's no upper bound on reconnection attempts. If the server keeps returning done=false (e.g., due to a bug where the stream never completes), this will loop indefinitely. Consider adding a maxReconnects counter (e.g., 50 — enough for ~100 minutes of streaming at 2-minute timeouts) with a warning log when exhausted.
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Fixed in 6ee6e7d — added MAX_RECONNECTS = 50 cap (~100 min at 2-min server timeout). Errors with a descriptive message when exhausted.
Signed-off-by: Peter Wielander <mittgfu@gmail.com>
- Propagate network errors via controller.error() instead of silently closing, so consumers know the stream was truncated - Add MAX_RECONNECTS (50) cap to prevent infinite loops if the server never completes the stream Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
The override was accidentally reset to empty in f92a411, causing e2e tests to hit production workflow-server which doesn't have the v3 stream endpoint yet. Restore to the preview deploy URL. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
This reverts commit 80c756f.
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TooTallNate
approved these changes
Apr 16, 2026
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All feedback addressed. LGTM.
What changed since my last review:
WORKFLOW_SERVER_URL_OVERRIDE— Reverted.utils.tsis no longer in the diff.- Error propagation —
controller.close()changed tocontroller.error(err)on network errors. Test updated to assertrejects.toThrow('connection reset'). - Reconnection cap — Added
MAX_RECONNECTS = 50(~100 min at 2-min timeouts). Errors with a clear message when exhausted.
All CI checks pass (unit tests on both ubuntu and windows, build, E2E).
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