fix(ast): count UTF-8 bytes without Node's Buffer by frontegg-david · Pull Request #92 · agentfront/enclave

frontegg-david · 2026-10-03T23:41:36Z

Stack 1/10: main ← this ← #93 ← #94 ← #95 ← #96 ← #98 ← #99 ← #100 ← #101 ← #102

Fixes #87.

Validation

Reproduced. In a plain browser, BrowserEnclave.run('return 1;') failed with ReferenceError: Buffer is not defined. The cause is Buffer.byteLength in @enclave-vm/ast: libs/ast/src/pre-scanner/checks/size-check.ts:21 and libs/ast/src/transforms/string-extraction.transform.ts (3 call sites). The browser e2e suite and the browser demo app hid it with an injected Buffer shim.

Fix

New libs/ast/src/utils/utf8-byte-length.ts. It counts UTF-8 bytes by walking the string, with the same counts as Buffer.byteLength (a lone surrogate is 3 bytes). It doesn't allocate a copy: the pre-scanner measures untrusted input before any other check, so new TextEncoder().encode(source) would allocate a buffer as big as the attack input.
Used by the size check and the string extraction transform.
Removed the Buffer shims from libs/browser/e2e/build-test-bundle.mjs and apps/browser-demo/scripts/build-enclave-bundle.mjs, so the e2e suite runs the package the way a browser does.

Red → green

Suite	Before (main sources)	After
`libs/ast/src/__tests__/utf8-byte-length.spec.ts` (new: parity with `Buffer.byteLength` on 10 samples, plus pre-scan, validation and extraction with `globalThis.Buffer` deleted)	4 failed (`ReferenceError: Buffer is not defined`), 10 passed	14 passed
Browser e2e without the shim	40 of 64 failed	64 passed (new: `validates without a Node.js Buffer global`)

Verification

npx jest -c libs/ast/jest.config.ts: 25 suites, 814 passed
npx nx run browser:test-e2e: 64 passed
yarn lint, yarn format:check, yarn build: pass (pre-existing warnings only)

🤖 Generated with Claude Code

Summary by CodeRabbit

Bug Fixes
- Input-size checks and string extraction now correctly count UTF-8 bytes, including multibyte characters and surrogate pairs.
- Browser-based validation works without a global Buffer, including when returning Unicode strings.

coderabbitai · 2026-10-03T23:41:52Z

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📥 Commits

Reviewing files that changed from the base of the PR and between 25b3e03 and 94f68ab.

📒 Files selected for processing (9)

apps/browser-demo/scripts/buffer-shim.mjs
apps/browser-demo/scripts/build-enclave-bundle.mjs
libs/ast/src/__tests__/utf8-byte-length.spec.ts
libs/ast/src/pre-scanner/checks/size-check.ts
libs/ast/src/transforms/string-extraction.transform.ts
libs/ast/src/utils/utf8-byte-length.ts
libs/browser/e2e/buffer-shim.mjs
libs/browser/e2e/build-test-bundle.mjs
libs/browser/e2e/validation.spec.ts

💤 Files with no reviewable changes (4)

libs/browser/e2e/build-test-bundle.mjs
apps/browser-demo/scripts/buffer-shim.mjs
libs/browser/e2e/buffer-shim.mjs
apps/browser-demo/scripts/build-enclave-bundle.mjs

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📝 Walkthrough

Walkthrough

The AST now uses a shared UTF-8 byte counter for input sizing and string extraction. Browser demo and e2e bundles no longer inject a Buffer shim. Tests cover sizing without a global Buffer and Unicode output in the browser.

Changes

Browser-compatible UTF-8 sizing

Layer / File(s)	Summary
UTF-8 byte counting in AST sizing `libs/ast/src/utils/utf8-byte-length.ts`, `libs/ast/src/pre-scanner/checks/size-check.ts`, `libs/ast/src/transforms/string-extraction.transform.ts`, `libs/ast/src/__tests__/utf8-byte-length.spec.ts`	The AST adds `utf8ByteLength` and uses it for input-size checks and string extraction byte counts. Tests compare byte counts with `Buffer.byteLength` and cover sizing and extraction when `Buffer` is absent.
Browser bundles without Buffer shim `apps/browser-demo/scripts/buffer-shim.mjs`, `apps/browser-demo/scripts/build-enclave-bundle.mjs`, `libs/browser/e2e/buffer-shim.mjs`, `libs/browser/e2e/build-test-bundle.mjs`, `libs/browser/e2e/validation.spec.ts`	The browser demo and e2e builds stop injecting the Buffer shim. An e2e test checks that `Buffer` is undefined and that code returning a Unicode string produces no error and returns that string.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Bug fix · Severity of issue fixed: Medium

Merge Risk: ⚪ Minimal · up to 94f68

No confirmed issue prevents merging. The browser validation test covers running a Unicode-returning script without a Buffer global.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Issue `#87` requires browser validation without a Node.js `Buffer` global. The PR replaces AST `Buffer.byteLength` calls with `utf8ByteLength`, removes the browser test and demo shims, and adds tests fo…
Out of Scope Changes check	✅ Passed	All reported changes support issue `#87`. The UTF-8 helper, AST call-site updates, shim removal, and unit and browser e2e tests implement or verify browser validation without a Node.js `Buffer` global. …
Docstring Coverage	✅ Passed	Docstring coverage is 80.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 5 functions across 5 files.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly describes the main change: counting UTF-8 bytes without relying on Node.js Buffer.

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@enclave-vm/browser could not validate any script in a plain browser: the pre-scanner's input size check and the string extraction transform called Buffer.byteLength, so run() failed with "Buffer is not defined". The browser e2e suite and the demo app hid it with an injected Buffer shim. Add an allocation-free utf8ByteLength helper (same counts as Buffer.byteLength, lone surrogates included), use it in both places, and drop the shims so the e2e suite runs the package as a browser would. Fixes #87 Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Copilot

Copilot review overview

🟢 Approval recommended

The implementation correctly preserves UTF-8 sizing semantics and includes focused unit and browser regression coverage.

Review effort: Balanced
Findings: None

What changed in this PR

Replaces Node-specific UTF-8 sizing in the AST package so browser validation works without a Buffer global.

Changes:

Adds allocation-free UTF-8 byte counting and adopts it across AST size checks and string extraction.
Removes browser/demo Buffer shims.
Adds unit and browser regression coverage.

File	Description
`libs/ast/src/utils/utf8-byte-length.ts`	Implements UTF-8 byte counting.
`libs/ast/src/pre-scanner/checks/size-check.ts`	Uses the browser-compatible utility.
`libs/ast/src/transforms/string-extraction.transform.ts`	Replaces `Buffer.byteLength` calls.
`libs/ast/src/__tests__/utf8-byte-length.spec.ts`	Tests parity and Buffer-free operation.
`libs/browser/e2e/validation.spec.ts`	Adds browser regression coverage.
`libs/browser/e2e/build-test-bundle.mjs`	Stops injecting the test shim.
`libs/browser/e2e/buffer-shim.mjs`	Removes the obsolete test shim.
`apps/browser-demo/scripts/build-enclave-bundle.mjs`	Stops injecting the demo shim.
`apps/browser-demo/scripts/buffer-shim.mjs`	Removes the obsolete demo shim.

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frontegg-david mentioned this pull request Oct 3, 2026

fix(browser): reject function-valued globals at construction #93

Merged

This was referenced Oct 3, 2026

fix(browser): sanitize script results like @enclave-vm/core #94

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fix(browser): apply core's timeout rules to tool calls #95

Merged

feat(core): accept a host-supplied sandboxAdapter #96

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frontegg-david added this pull request to stack #97 October 3, 2026 23:55

frontegg-david requested a balanced review from Copilot October 3, 2026 23:56

frontegg-david force-pushed the fix/ast-utf8-byte-length-without-buffer branch from 94f68ab to 6f04820 Compare October 3, 2026 23:56

Copilot started reviewing on behalf of frontegg-david October 3, 2026 23:56

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Copilot AI reviewed Oct 3, 2026

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This was referenced Oct 4, 2026

fix(core): return Dates from the single VM as Dates #98

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ci: run the browser Playwright suite #99

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alexmercerpo approved these changes Oct 4, 2026

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This was referenced Oct 4, 2026

fix(core): convert worker results like the other adapters #100

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chore(deps): update Nx to 22.7.12 #101

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chore(deps): update vulnerable transitive dependencies #102

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frontegg-david merged commit a909613 into main Oct 4, 2026
8 checks passed

frontegg-david deleted the fix/ast-utf8-byte-length-without-buffer branch October 4, 2026 10:55

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fix(ast): count UTF-8 bytes without Node's Buffer - #92

fix(ast): count UTF-8 bytes without Node's Buffer#92
frontegg-david merged 1 commit into
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fix/ast-utf8-byte-length-without-buffer

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Validation

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frontegg-david commented Oct 3, 2026 •

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