fix(driver-utils): prevent unhandled rejection in getSnapshotTree prefetch by anthony-murphy-agent · Pull Request #26173 · microsoft/FluidFramework

anthony-murphy-agent · 2026-01-09T20:17:32Z

Summary

Fix unhandled promise rejections in PrefetchDocumentStorageService fire-and-forget calls
Add unit test for getSnapshotTree failure scenario

Problem

This is a follow-up to PR #26151. After that fix was deployed, telemetry showed 349 uncaughtException errors from ShreddedSummaryDocumentStorageService.readBlob in test-service-load tinylicious tests.

Root cause: PR #26151 attached .catch() to the inner promise in cachedRead(), but that only handles ONE promise chain. The fire-and-forget callers create a DIFFERENT chain:

void this.cachedRead(blob) - cachedRead is async, so it returns a NEW promise wrapping the inner promise. The .catch() on the inner promise doesn't prevent unhandled rejection on the async function's returned promise.
void p.then(...) in getSnapshotTree() - creates a derived promise that also rejects when p rejects.

Solution

Fix all three fire-and-forget patterns:

// Before (inner promise handled, but async wrapper not):
void this.cachedRead(blob);

// After (handles the async function's returned promise):
this.cachedRead(blob).catch(() => {});

// Before (derived promise not handled):
void p.then((tree) => this.prefetchTree(tree));

// After (handles the derived promise):
void p.then(...).catch(() => {});

Test plan

New unit test for getSnapshotTree failure scenario
All 5 PrefetchDocumentStorageService tests pass
Build passes

🤖 Generated with Claude Code

Co-Authored-By: anthony-murphy anthony.murphy@microsoft.com

anthony-murphy · 2026-01-09T20:19:45Z

/azp run Build - api-markdown-documenter, Build - benchmark-tool, Build - build-common, Build - build-tools, Build - client packages, Build - common-utils, Build - eslint-config-fluid, Build - eslint-plugin-fluid, Build - protocol-definitions, Build - test-tools

azure-pipelines · 2026-01-09T20:20:05Z

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anthony-murphy · 2026-01-09T20:20:59Z

/azp run repo-policy-check, server-gitrest, server-gitssh, server-historian, server-routerlicious

azure-pipelines · 2026-01-09T20:21:10Z

Azure Pipelines successfully started running 1 pipeline(s).

Copilot

Pull request overview

This PR fixes an unhandled promise rejection bug in PrefetchDocumentStorageService.getSnapshotTree() by adding a .catch() handler to the fire-and-forget prefetch pattern. This is a follow-up to PR #26151, which fixed a similar issue in cachedRead() but missed this code path.

Adds .catch() handler to prevent unhandled rejections when getSnapshotTree() fails
Adds unit test to verify the fix and ensure errors are still properly propagated to callers

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
packages/loader/driver-utils/src/prefetchDocumentStorageService.ts	Adds `.catch()` handler to fire-and-forget prefetch pattern in `getSnapshotTree()` to prevent unhandled rejections while still propagating errors to callers
packages/loader/driver-utils/src/test/prefetchDocumentStorageService.spec.ts	Adds mock failure flags and test case to verify `getSnapshotTree()` failures don't cause unhandled rejections

…orget calls Fix three fire-and-forget patterns that cause unhandled rejections: 1. getSnapshotTree(): `void p.then(...)` creates a derived promise that rejects when p rejects. Added `.catch()` to the promise chain. 2. prefetchTree()/prefetchTreeCore(): `void this.cachedRead(blob)` discards the async function's returned promise. Since cachedRead is async, it returns a separate promise chain from the inner prefetchedBlobPFromStorage. The existing `.catch()` inside cachedRead only handles the inner promise, not the async function's returned promise. Changed to `this.cachedRead(blob).catch(() => {})`. The root cause: attaching `.catch()` to a promise P only prevents unhandled rejection for P's chain. When an async function returns P, the function's returned promise is a DIFFERENT chain that also rejects - and needs its own `.catch()` handler. This is a follow-up to PR microsoft#26151 which only fixed the inner promise in cachedRead but didn't fix the callers' fire-and-forget patterns. Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com> Co-Authored-By: anthony-murphy <anthony.murphy@microsoft.com>

packages/loader/driver-utils/src/prefetchDocumentStorageService.ts

Address review comment - void is no longer needed since .catch() handles the promise rejection, so there's no floating promise issue. Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com> Co-Authored-By: anthony-murphy <anthony.murphy@microsoft.com>

anthony-murphy-agent · 2026-01-09T20:45:46Z

Azure Pipelines commands (copy and post separately, limit of 10 at a time):

/azp run Build - api-markdown-documenter, Build - benchmark-tool, Build - build-common, Build - build-tools, Build - client packages, Build - common-utils, Build - eslint-config-fluid, Build - eslint-plugin-fluid, Build - protocol-definitions, Build - test-tools

/azp run repo-policy-check, server-gitrest, server-gitssh, server-historian, server-routerlicious

anthony-murphy · 2026-01-09T20:46:23Z

/azp run Build - api-markdown-documenter, Build - benchmark-tool, Build - build-common, Build - build-tools, Build - client packages, Build - common-utils, Build - eslint-config-fluid, Build - eslint-plugin-fluid, Build - protocol-definitions, Build - test-tools

azure-pipelines · 2026-01-09T20:46:42Z

Azure Pipelines successfully started running 1 pipeline(s).

anthony-murphy · 2026-01-09T20:48:09Z

/azp run repo-policy-check, server-gitrest, server-gitssh, server-historian, server-routerlicious

azure-pipelines · 2026-01-09T20:48:21Z

Azure Pipelines successfully started running 1 pipeline(s).

Copilot

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

…fetch (microsoft#26173) ## Summary - Fix unhandled promise rejections in `PrefetchDocumentStorageService` fire-and-forget calls - Add unit test for getSnapshotTree failure scenario ## Problem This is a follow-up to PR microsoft#26151. After that fix was deployed, telemetry showed 349 `uncaughtException` errors from `ShreddedSummaryDocumentStorageService.readBlob` in test-service-load tinylicious tests. **Root cause:** PR microsoft#26151 attached `.catch()` to the inner promise in `cachedRead()`, but that only handles ONE promise chain. The fire-and-forget callers create a DIFFERENT chain: 1. **`void this.cachedRead(blob)`** - `cachedRead` is async, so it returns a NEW promise wrapping the inner promise. The `.catch()` on the inner promise doesn't prevent unhandled rejection on the async function's returned promise. 2. **`void p.then(...)`** in `getSnapshotTree()` - creates a derived promise that also rejects when `p` rejects. ## Solution Fix all three fire-and-forget patterns: ```typescript // Before (inner promise handled, but async wrapper not): void this.cachedRead(blob); // After (handles the async function's returned promise): this.cachedRead(blob).catch(() => {}); ``` ```typescript // Before (derived promise not handled): void p.then((tree) => this.prefetchTree(tree)); // After (handles the derived promise): void p.then(...).catch(() => {}); ``` ## Test plan - [x] New unit test for `getSnapshotTree` failure scenario - [x] All 5 PrefetchDocumentStorageService tests pass - [x] Build passes 🤖 Generated with [Claude Code](https://claude.ai/code) Co-Authored-By: anthony-murphy <anthony.murphy@microsoft.com> --------- Co-authored-by: anthony-murphy-agent <253562292+anthony-murphy-agent@users.noreply.github.com> Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com> Co-authored-by: anthony-murphy <anthony.murphy@microsoft.com>

jzaffiro approved these changes Jan 9, 2026

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anthony-murphy requested a review from Copilot January 9, 2026 20:21

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anthony-murphy-agent force-pushed the fix/prefetch-unhandled-rejection branch from 907fe32 to a3e582d Compare January 9, 2026 20:40

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anthony-murphy requested a review from Copilot January 9, 2026 20:46

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anthony-murphy enabled auto-merge (squash) January 9, 2026 20:52

anthony-murphy approved these changes Jan 9, 2026

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anthony-murphy merged commit 6f218b3 into microsoft:main Jan 9, 2026
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fix(driver-utils): prevent unhandled rejection in getSnapshotTree prefetch#26173

fix(driver-utils): prevent unhandled rejection in getSnapshotTree prefetch#26173
anthony-murphy merged 2 commits intomicrosoft:mainfrom
anthony-murphy-agent:fix/prefetch-unhandled-rejection

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