css: reject stylesheets of 2 GiB or more instead of aborting on an int cast

[robobun]

Problem

• A .css input of 2 GiB or more aborts bun build and Bun.build with panic: int cast: TryFromIntError(PosOverflow). Found by inspection during Reject sources of 2 GiB or more before parsing instead of aborting in usize2loc #39095, no user report.
• bun_css casts offsets, lines and columns to i32 with expect("int cast"): src/css/css_parser.rs:3102, src/css/properties/css_modules.rs:50, src/css/error.rs:190.

Fix

• parse_with, StyleAttribute::parse and Bun.color reject input longer than MAX_INPUT_LEN: CSS file is too large to parse (2 GiB maximum). MAX_INPUT_LEN is i32::MAX - 1, one below Source::MAX_PARSEABLE_LEN (src/ast/lib.rs:2591): a column at the end of input is len + 1.
• add_import_record stored the unescaped url() length as the record range. Raw NULs expand to 3-byte U+FFFD, so it can pass i32::MAX under the limit. It now stores the source span, as on_import_rule does. That input still aborts elsewhere (Downsides).
• Verified: test/js/bun/css/input-too-large.test.ts (five cases, Notes), test/bundler/css, test/js/bun/css. Self-reviewed: 3 concerns, 3 addressed.

Background

• bun_ast::Loc is the i32 byte offset the pipeline uses, so every parser has a 2 GiB ceiling. Nothing bounded CSS input.
• ImportRecord.range is the source range a resolve error reports.

Downsides

• position.length of a CSS resolve error becomes the token's source span: url("./a\30 .png") reports 24, not 14. Nothing reads it.
• A url() of about 716 MiB of raw NULs still aborts, in the resolver: src/resolver/package_json.rs:1371 casts the specifier length to i32.
• The tests take 25 to 30 s in a debug build: four children of 2 to 4.4 GiB gated on 10 GiB of memory, one 8.3 GiB child on 16 GiB.

Notes

The error has no position, so Err::add_to_logger gives a positionless error a file-only location (init_or_null with Range::NONE). Only this error takes that branch. bun build --no-bundle formats only the text, as error: <message> parsing.

Test cases, each a child process that gets a stylesheet of one comment followed by .a{composes:b}:

1. Bun.build with an in-memory file of 2**31 + 17 bytes. The composes sits past byte 2**31. Without the fix: the panic above, after a 2 GiB tokenize. With it: success: false and one error with position.file set. Runs on Windows too (zero pages of a Uint8Array).

2. Bun.build with exactly MAX_INPUT_LEN + 1 bytes. Every offset in it fits an i32, so without the fix it parses. With it, it is rejected. The at-limit side (MAX_INPUT_LEN bytes parse) is not tested: tokenizing 2 GiB takes about 4 minutes in a debug build (256 MiB took 31 s).

3. bun build --no-bundle on a sparse file of the same shape (8 KiB on disk, not on Windows). Exact stderr: error: CSS file is too large to parse (2 GiB maximum) parsing. The parsing suffix is pre-existing for every CSS error on that path (src/bundler/transpiler.rs:3192) and left alone.

4. StyleAttribute::parse through bun:internal-for-testing, its only caller. A JS string holds at most 2**31 - 1 code units, so the tail is Latin-1 é characters that grow in UTF-8 and put the composes past byte 2**31. Without the fix: the panic. With it: parsing failed: CSS file is too large to parse (2 GiB maximum). 8 to 11 s in a debug build. The transcode holds the Buffer, the string and two UTF-8 buffers at once, hence the 8.3 GiB peak and the separate 16 GiB gate.

5. Bun.color on the longest JS string, 2**31 - 1 ASCII chars, which is MAX_INPUT_LEN + 1 bytes and borrows with no transcode. Without the fix: null (an invalid color). With it: the throw. 4 s and 4.4 GiB in a debug build. A non-ASCII string was tried first: its Latin-1 to UTF-8 transcode takes 120 s in a debug build.

Debug-build times: 3.8 s, 3.5 s, 5.7 s, 11 s, 4 s. The default per-test budget is 5 s, so the file sets one shared 30 s timeout.

The NUL url() case was verified by hand: .a{background:url("<716 MiB of NUL>")} aborts bun 1.4.3 in add_import_record, and aborts this build in the resolver instead (stack: Package::parse_name from Resolver::load_node_modules). It is not a test: about 10 minutes and 12 GiB in a debug build.

test/js/bun/css as a whole shows timeouts of tests that spawn children loading bun:internal-for-testing (about 1.7 s each) when the directory runs in parallel under this debug ASAN build. Each passes alone.

Self-review concerns: the attribute case's memory (gated on 16 GiB), the one-byte difference from Source::MAX_PARSEABLE_LEN (stated above), and the span change's effect on position.length and its limits (stated above). A later review named Bun.color (src/css_jsc/color_js.rs) as the third parser entry over user bytes, now covered. The other ParserInput::new callers parse slices of an already bounded stylesheet.

Repro:

bun -e '
const fs = require("fs");
const fd = fs.openSync("big.css", "w");
fs.writeSync(fd, Buffer.from("/*"), 0, 2, 0);
const tail = Buffer.from("*/.a{composes:b}\n");
fs.writeSync(fd, tail, 0, tail.length, 2 ** 31);   // sparse: 8 KiB on disk
fs.closeSync(fd);'
bun build ./big.css --outdir out             # before: panic: int cast: TryFromIntError(PosOverflow), exit 134
bun build --no-bundle ./big.css              # before: same panic

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no test proof · iteration 0 · platform-specific test(s) that do not run on this machine, deferring to CI, which covers all platforms: test/js/bun/css/input-too-large.test.ts

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• src/css/css_parser.rs
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Walkthrough

CSS stylesheet, style-attribute, and Bun.color parsing now reject input above i32::MAX - 1. Errors without a stored location receive a file-level location. URL import records use the consumed source span for their range length.

Changes

CSS parser handling

Layer / File(s)	Summary
Parser validation, errors, and source ranges src/css/css_parser.rs, src/css/error.rs, src/css_jsc/color_js.rs, test/js/bun/css/input-too-large.test.ts	Stylesheet, style-attribute, and Bun.color parsing reject oversized input and report the shared size error. Errors without a stored location receive a file-level location. URL import ranges use the consumed source span. Tests cover oversized input through Bun.build, bun build --no-bundle, style-attribute parsing, and Bun.color.

Suggested reviewers: jarred-sumner

Priority: ➖ Normal

Merge Risk: 🔵 Low · up to 6a971

The change rejects oversized CSS and color input with a clear error instead of aborting. The only open concern is a minor test-guideline issue: the new tests set explicit timeouts, which should be removed. It is low risk and does not block the fix.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly describes the main change: rejecting oversized CSS stylesheets instead of aborting on an integer cast. It does not mention every affected entry point, but it remains specific and rel…
Description check	✅ Passed	The description provides detailed problem, fix, verification, test coverage, limitations, and reproduction information. It does not use the required headings "### What does this PR do?" and "### How d…

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[robobun]

^{Updated 11:47 PM PT - Sep 30th, 2026}

✅ @robobun, your commit 6a971b3a9607027b8e6ebdd268d0c244af006d11 passed in Build #122219! 🎉

---

🧪   To try this PR locally:

bunx bun-pr 39113

That installs a local version of the PR into your bun-39113 executable, so you can run:

bun-39113 --bun

[robobun]

Status: fix and test pushed, waiting on CI.

Reproduced on 1.4.0 with a sparse 2 GiB .css file (a comment covering the first 2 GiB, then .a{composes:b}): bun build big.css --outdir out and bun build --no-bundle big.css both abort with panic: int cast: TryFromIntError(PosOverflow). With this branch both exit 1 with error: CSS file is too large to parse (2 GiB maximum).

The new test (test/js/bun/css/input-too-large.test.ts) fails the same way on the unfixed binary and passes with the fix, for both callers of bun_css (Bun.build and bun build --no-bundle).

Companion to #39095, which adds the same limit to the JS, TOML, YAML and XML parsers; the two touch different files.

[claude]

LGTM — converts a user-reachable panic on ≥2 GiB CSS input into a recoverable build error, matching the JSON parser's precedent.

What was reviewed:

• Length check placement in parse_with and StyleAttribute::parse — runs before any read of code; return type matches so ? propagates cleanly.
• init_or_null with Range::NONE takes the is_empty() early return, so the file-only location does not scan the oversized source.contents.
• Other loc: None producers (PrinterError::fmt_error / no_import_records) — attaching a file-only location if they ever reach add_to_logger is a strict improvement, not a regression.
• Test follows harness conventions: memory gate mirrors fs-oom.test.ts, pipes drained concurrently, Windows skip on the sparse-file case is justified, per-test timeouts commented.

Extended reasoning...

Overview

The PR adds an up-front length bound (MAX_INPUT_LEN = i32::MAX - 1) at the two CSS parser entry points (StyleSheet::parse_with and StyleAttribute::parse), a new ParserError::input_too_large variant with a Display arm, and changes Err::add_to_logger to emit a file-only bun_ast::Location when loc is None. A new test file exercises both the Bun.build and bun build --no-bundle paths with a 2 GiB comment plus a composes declaration.

Security risks

None introduced. This is a defensive hardening change: it removes a user-reachable panic (which REVIEW.md classes as a DoS) and replaces it with a graceful error. No new parsing, no new trust of input, no new allocation before validation.

Level of scrutiny

Low-to-medium. The Rust change is ~25 lines: a const, a 7-line guard function called at two entry points, one enum variant + match arm, and one line in add_to_logger. I verified that bun_ast::Location::init_or_null(Some(source), Range::NONE) short-circuits on r.is_empty() (src/ast/lib.rs:767) and returns a file-only location without touching source.contents, so the positionless error path does not scan the 2 GiB buffer. The i32::MAX - 1 bound is correctly justified in the doc comment (accounts for len + 1 cases: 1-based line count / column at EOF).

Other factors

• The wording and limit match the existing JSON parser message ("... too large to parse (2 GiB maximum)"), and the PR description notes #39095 does the same for JS/TOML/YAML/XML — this is the CSS sibling.
• The only other loc: None producers in the crate are PrinterErrorKind::fmt_error and no_import_records; the add_to_logger change would give those a file name too if they ever flow through it, which is not a behavior regression.
• Tests follow the repo's harness conventions closely: bunEnv/bunExe/tempDir, concurrent pipe draining via Promise.all, stderr/stdout asserted before exitCode, describe.skipIf on total memory (same 10 GiB gate as fs-oom.test.ts), a commented reason for the Windows skip on the sparse-file case, and a comment explaining why the tests are serial and have 30 s timeouts.
• The PR description states the tests were verified to fail under USE_SYSTEM_BUN=1 and pass under bun bd, and that the existing CSS suites still pass modulo pre-existing debug-ASAN timeouts.

[claude]

Nothing blocking. The comments below are optional suggestions. There is no need to push a fix for them before merging.

Beyond the inline findings, I also checked the third parser entry point, Bun.color (src/css_jsc/color_js.rs:330-337), for the same missing length check: it builds a bare Parser and only runs CssColor::parse, which never reaches the i32 cast sites (import records, composes, CSS-module identifiers) or the logger location conversion, so it does not need check_input_len.

Extended reasoning...

The change adds a length guard (MAX_INPUT_LEN = i32::MAX - 1) at the top of StyleSheet::parse_with and StyleAttribute::parse in src/css/css_parser.rs, a new ParserError::input_too_large variant, a file-only logger location for positionless errors in src/css/error.rs, and a memory-gated test file. It touches no security-sensitive surface; the guard runs before any input is read. Four verified findings are posted inline (test-side gaps and a missing sibling-entry-point test), so approval is not appropriate; this note only records the one additional entry point examined and ruled out.

[claude]

Nothing blocking. The comments below are optional suggestions. There is no need to push a fix for them before merging.

Beyond the inline findings, I also checked whether the loc: None -> init_or_null(Some(source), Range::NONE) change in Err::add_to_logger (src/css/error.rs:77) alters any existing diagnostic: add_to_logger is only called from the bundler's parse and minify error paths (src/bundler/ParseTask.rs:1316, :1337), and the only other positionless Err constructions in the crate are the printer's fmt_error / no_import_records (src/css/printer.rs:234, :242), which do not go through that function — so only the new input_too_large error gets the file-only location.

Extended reasoning...

The change adds a length guard at both CSS parse entry points, a new ParserError variant, and a file-only location for positionless errors; the ruled-out note records that the location change cannot reach any pre-existing diagnostic, since no other loc-less error flows through add_to_logger.

Still open from earlier reviews (4):

• Unresolved: 4 minor or pre-existing.

Additional findings (outside the current diff — GitHub can't attach inline comments there):

• 🟣 src/css/css_parser.rs — pre-existing: bundling a CSS file well under the new 2 GiB limit still aborts with panic: int cast when one url() holds enough NUL bytes. check_input_len bounds source bytes, but src/css/css_parser.rs:3105 casts url.len(), the unescaped token, and the tokenizer expands each raw NUL to the 3-byte U+FFFD. So about 683 MiB of NULs inside a url() yields a length past i32::MAX. Fix: store a source span as the record length (self.position() - start_position, which the TODO on that line already asks for) or clamp it, so every add_import_record caller is covered (url.rs:21, image.rs:393, custom.rs:55, css_modules.rs:156).

  Why this was flagged

  A stylesheet such as .a{background:url("<715,827,883 NUL bytes>")} (about 683 MiB, under MAX_INPUT_LEN at src/css/css_parser.rs:2335) reaches parse_bundler from src/bundler/ParseTask.rs:1306 for bun build / Bun.build. consume_quoted_string at src/css/css_parser.rs:4702-4705 and consume_unquoted_url at :4838-4841 replace every raw 0x00 byte with REPLACEMENT_CHAR_UNICODE (3 bytes), so the token value is three times longer than its source span. Url::parse at src/css/values/url.rs:21 hands that value to add_import_record, and src/css/css_parser.rs:3105 does i32::try_from(url.len()).expect("int cast"), which panics once the expanded length exceeds 2^31-1. The PR's guard at :2338 only compares code.len(), so it does not cover this cast. The base branch panics the same way, so this is a remaining site of the class the PR sets out to close rather than a regression; the same helper is also reached from src/css/values/image.rs:393, src/css/properties/custom.rs:55 and src/css/properties/css_modules.rs:156.

  Verification: pre-existing (base has the identical cast at the pre-PR line 3090, so the same input aborts the base by the same route). Trigger: bun build / Bun.build on a stylesheet under MAX_INPUT_LEN whose url() contains ~716M raw NUL bytes. check_input_len (src/css/css_parser.rs:2335-2343) bounds only code.len(), while :3105 does i32::try_from(url.len()).expect("int cast") on the UNESCAPED token value, where each raw 0x00 byte becomes the 3-byte REPLACEMENT_CHAR_UNICODE.

[claude]

Nothing blocking. The comments below are optional suggestions. There is no need to push a fix for them before merging.

Beyond the inline finding, I also checked the new end_position - start_position span in add_import_record (src/css/css_parser.rs:3099-3107): all four callers (values/url.rs, values/image.rs, properties/custom.rs, properties/css_modules.rs) take start_position from input.position() before consuming the url/string token, so the subtraction cannot underflow and stays within MAX_INPUT_LEN. I also looked at the one user-reachable parser entry that bypasses check_input_len, Bun.color at src/css_jsc/color_js.rs:330: it parses only a color, creates no import records, symbols, or logger locations, so it reaches none of the i32 casts and is not affected.

Extended reasoning...

The latest push (07467b0) addressed the earlier feedback: a named CHILD_TIMEOUT constant with a measured-time comment, a MAX_INPUT_LEN + 1 case, exact toBe stderr assertions, a StyleAttribute::parse case, and a constrainedMemory-aware gate. The remaining concern is the inline finding about the new attrTest child's peak memory on 10-12 GiB runners; nothing else in the Rust changes stood out.

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Actionable comments posted: 1

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• 🪄 Fix CodeRabbit comments on this PR

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Inline comments:
Review comments at @test/js/bun/css/input-too-large.test.ts:
- Around line 56-74: Remove the explicit CHILD_TIMEOUT argument from each of the
four input-size tests and delete the now-unused CHILD_TIMEOUT constant; update
the header comment to no longer mention the timeout, while leaving each test’s
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• src/css/css_parser.rs
• src/css/error.rs
• test/js/bun/css/input-too-large.test.ts

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[claude]

Nothing blocking. The comments below are optional suggestions. There is no need to push a fix for them before merging.

Beyond the inline finding, I also checked the widened None arm in Err::add_to_logger (src/css/error.rs:78): add_to_logger is only called from the two sites in src/bundler/ParseTask.rs, and the only loc: None constructions in src/css besides the new variant are the two PrinterErrors in src/css/printer.rs, which never reach that function, so the file-only location applies to the new error alone. The remaining i32::try_from(end_position - start_position) at src/css/css_parser.rs:3106 is bounded by check_input_len on every path through parse_with, so it is a provable invariant there.

Extended reasoning...

The change adds a 2 GiB input guard to the two StyleSheet/StyleAttribute parse entry points, a new ParserError variant with a file-only log location, and switches the @ import record length to the source span; no auth, crypto, or injection surface is touched. A verified finding about a third unguarded parser entry point (Bun.color) is posted inline, and a further verified finding is unposted, so approval is not appropriate; this note only records what else was examined.

[claude]

Code review found no issues

No high-confidence issues detected in this change.