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Status: reproduced all three divergences on bun 1.4.3 against node v26.3.0 with standalone scripts (the probe table is in the PR body). The fix is in the PR, rebased onto current main. Tests: CI: the diff is green across three runs (177 of 181 jobs on the latest). The red lanes are unrelated to this change: a Verdaccio registry fixture that exits with code 2 on some Linux lanes ( |
WalkthroughChangesBuffer range validation now supports safe-integer offsets and buffer-specific end limits. Detached-buffer searches treat the haystack as empty. Buffer inspection delegates property formatting to Suggested reviewers: Merge Risk: ⚪ Minimal · up to This updates Buffer range handling, detached-buffer searches, and inspection formatting for Node compatibility. The covered behavior is ready to merge with no remaining product-facing risk identified. 🚥 Pre-merge checks | ✅ 4✅ Passed checks (4 passed)
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Inline comments:
In `@test/js/node/buffer.test.js`:
- Line 5445: Replace the loops parameterizing offset and start values in the
relevant buffer tests with describe.each() blocks, so every independent value
produces a separate test result while preserving the existing assertions and
coverage. Apply this to both the offset and start cases near the affected test
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Updated 6:45 AM PT - Sep 6th, 2026
❌ @robobun, your commit 2672ca0 has 4 failures in
🧪 To try this PR locally: bunx bun-pr 41498That installs a local version of the PR into your bun-41498 --bun |
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Re-reviewed after f3538d2 and 69f5cf3 — both of my earlier inline findings are addressed: compare() now validates targetStart → targetEnd → sourceStart → sourceEnd in argument order (with a test pinning which name ERR_OUT_OF_RANGE reports on doubly-invalid input), and the inspect-extras path now copies ctx via putDirectMayBeIndex with a prototype-pollution test. I didn't find further issues, but given this is hand-written JSC binding C++ on Buffer.prototype (re-entrant util.inspect call, detached-buffer read paths), a human pass is still worthwhile.
What was reviewed
compare()rewrite: argument-order validation,MAX_SAFE_INTEGERstart bounds, per-buffer end bounds; the empty-range early return below still guardsmemcmp.refetchBufferState: confirmedcomputeIndexOfRange's length-0 branches return before anytypedVectordereference, so the null vector on detach is not read.- Inspect extras:
RETURN_IF_EXCEPTIONpresent after eachget/getOwnPropertyNames/call/toWTFString;extrasuses null-prototype structure soputDirecton it can't hit a setter;Bun__inspect_singlelinestill has callers inErrorCode.cppandJSMessageEvent.cpp, so removing only the local extern is correct.
Extended reasoning...
Overview
Four Node-compat fixes in src/jsc/bindings/JSBuffer.cpp with tests appended to test/js/node/buffer.test.js: compare() offset validation rewritten to argument order with MAX_SAFE_INTEGER start bounds and per-buffer end bounds; fill() offset bound raised to MAX_SAFE_INTEGER; indexOf/lastIndexOf/includes now treat a detached haystack as empty instead of returning -1 unconditionally; and the [util.inspect.custom] hook now delegates extra own-property formatting to a single util.inspect call on a null-prototype copy, slicing the [Object: null prototype] { ... } wrapper off the result. The unused local Bun__inspect_singleline extern is dropped.
Security risks
None identified. The detached-buffer path sets typedVector = nullptr, len = 0 and relies on computeIndexOfRange short-circuiting before any memory read when the haystack length is 0 — I traced that this holds for the number, string, and Uint8Array needle branches. The inspect path calls back into JS (util.inspect), which is re-entrant, but every call site has RETURN_IF_EXCEPTION and no raw buffer pointers are held across it (the hex-byte loop finished earlier). The options object is built with putDirect/putDirectMayBeIndex (define semantics), so Object.prototype setters are not invoked — this was my earlier objection and is now fixed with a covering test.
Level of scrutiny
High. This is hand-written C++ against JSC internals on Buffer.prototype methods — the "most-blocked category" per REVIEW.md. The inspect change introduces a re-entrant call into util.inspect from native code and a string-prefix-slicing heuristic on its output; the detached-indexOf change removes an early return in a path that later reads a possibly-null vector pointer. Both warrant a maintainer's eyes even though I found no defect.
Other factors
Both inline findings from my previous review were addressed by follow-up commits, each with a dedicated regression test (compare() names the first invalid offset in argument order and builds its inspect options without running setters on Object.prototype). Several github-actions[bot] inline threads were resolved by the PR author; I cannot see their content and author-self-resolution is not independent evidence they were addressed, which is another reason to keep a human in the loop rather than approve outright. Test coverage for the new behavior is thorough (offset boundary matrix, detached vs. empty equivalence table, colors/depth/showHidden variants, prototype-pollution guard).
…Of, and inspect extras - fill() and compare() bound a start offset by 2**53 - 1 like Node's validateOffset, so a start past the end is an empty range instead of ERR_OUT_OF_RANGE. An end is validated against its buffer's length in the same call, which also gives it Node's message. - indexOf, lastIndexOf and includes treat a detached buffer as an empty one: an empty needle is found at 0. - Buffer.prototype[inspect.custom] formats extra own properties through util.inspect on a null-prototype object, like Node, so keys and values get the same quoting, colors and depth as the surrounding output.
…ons copies Node names the first invalid offset in argument order (targetStart, targetEnd, sourceStart, sourceEnd). The fallthrough switch validated them in reverse, so two invalid ends named sourceEnd. The inspect options object is now built with define semantics, like the spread in Node, so a setter on Object.prototype under an option name does not run.
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Problem
Three
node:bufferbehaviors differ from Node v26.3.0, all insrc/jsc/bindings/JSBuffer.cpp:buf.fill(v, offset)andbuf.compare(t, targetStart, ..., sourceStart)throwERR_OUT_OF_RANGEfor a start above 232 (jsBufferPrototypeFunction_fillBody,jsBufferPrototypeFunction_compareBody). Node bounds a start by its kMaxLength (253 - 1) and treats a start past the end as an empty range. Bun used its own kMaxLength (2**32). The end check incomparealso printed>= 0 and <= 3instead of Node's>= 0 && <= 3.indexOf(''),lastIndexOf('')andincludes('')return -1 / false on a detached Buffer (refetchBufferStateinindexOf). Node reads a detached Buffer as empty, so an empty needle is found at 0.util.inspect(buf)with extra own properties prints<Buffer 03, x: "y">(double quotes, unquoteda-bkeys, bare symbol names, no depth limit, no colors). Node prints<Buffer 03, x: 'y'>. Bun formatted each value withBun__inspect_singleline.Fix
fillandcomparevalidate a start withvalidateInteger(0, kMaxOffset)like Node'svalidateOffset, in argument order.kMaxOffsetis a new named constant inJSBuffer.h(253 - 1, Node'skMaxLengthsince deps: update V8 to 12.4 nodejs/node#52465). It is separate from Bun'skMaxLength(232), which bounds an allocation size and stays in place forallocandBuffer.concat.comparevalidates an end against its own buffer's length in the same call, which gives Node's message.refetchBufferStateno longer short-circuits a detached haystack to -1. It sets length 0, andcomputeIndexOfRangealready handles an empty haystack without reading the vector.util.inspecton it with the caller's options plusbreakLength: Infinity, compact: true, and keeps the text between[Object: null prototype] {and}. This is Node'sBuffer.prototype[inspect.custom], so keys, values, colors and depth match.test/js/node/buffer.test.js(8 new tests fail on bun 1.4.3, all 688 pass here). Also Node'stest-buffer-{fill,compare,compare-offset,indexof,includes,inspect,prototype-inspect,alloc}.js,util-inspect.test.js,console-log.test.ts.Background
Bun::V::validateIntegeris the port of Node'svalidateInteger(value, name, min, max). It throwsERR_OUT_OF_RANGEwith>= min && <= max.Bun::Buffer::kMaxLengthisMAX_ARRAY_BUFFER_SIZE(2**32) because JSC caps anArrayBufferthere. It is the right bound for an allocation size (alloc,concat), not for a start offset, which can never index past a real buffer and is an empty range in Node.byteLength()0 and a null vector.computeIndexOfRangereturns an immediate result for an empty haystack or an empty needle, so the search code never reads the vector.globalObject->utilInspectFunction()isnode:util'sinspect, the same functioninternal/util/inspect.jspasses to a custom inspect hook.Notes
Node reference:
validateOffsetinlib/buffer.js(validateInteger(value, name, 0, kMaxLength)withkMaxLength = 2**53 - 1),_fill(validateOffset(offset, 'offset'),validateOffset(end, 'end', 0, buf.length), thenif (offset >= end) return buf),compare(validateOffset(targetEnd, 'targetEnd', 0, target.length)),IndexOfOffsetinsrc/node_buffer.cc(empty needle past the end points at the end), andBuffer.prototype[customInspectSymbol].Probe on node v26.3.0 vs bun 1.4.3, all now identical on this build:
Review follow-ups in this PR:
compare()validates its offsets in argument order so the first invalid one is the one named (the switch used to run in reverse), and the inspect options copy uses define semantics so a setter onObject.prototypeunder an option name does not run. Both have tests.Bun.inspect(buf)keeps its own default depth (8), so the test passes{ depth: 2 }to the native formatter.console.log(buf)uses depth 2 and matches Node.Related open PRs for the other rows of the same report: #39073 (
toJSONon a detached Buffer), #39028 (isUtf8/isAsciiwith a DataView). #36138 (%sof a Buffer) merged.no test proof · iteration 3 · platform-specific test(s) that do not run on this machine, deferring to CI, which covers all platforms: test/js/node/buffer.test.js