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bundler(html): percent-encode output paths written into src and href, and serve them under that name - #41793
bundler(html): percent-encode output paths written into src and href, and serve them under that name#41793robobun wants to merge 10 commits into
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An asset or chunk whose output name contains a space, '#', '?', '%' or a non-ASCII byte was written into the rewritten <img src>, <script src> and <link href> as raw bytes. A browser parses that value as a URL, so "./shot #1-6wrh68hc.png" is cut at the '#' and the request for "./shot%20" misses the file. HTML chunks now percent-encode the path they splice in for each asset and chunk reference (the WHATWG path percent-encode set plus '%' and '\\'), so the emitted URL decodes back to the file on disk. JS and CSS output is unchanged.
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Reproduced on 1.4.3-canary (f42e980): printf PNG1 > 'shot #1?.png'; printf PNG2 > 'my photo.png'
echo '<!doctype html><html><body><img src="./my photo.png"><img src="./shot #1?.png"></body></html>' > index.html
bun build ./index.html --outdir o && grep -o '<img[^>]*>' o/index.html
# <img src="./my photo-crx865yh.png"> <img src="./shot #1?-6wrh68hc.png">
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WalkthroughHTML bundler output now percent-encodes rewritten asset paths and escapes ampersands in HTML attributes. Bundled-file routes register encoded and raw paths. Tests cover special-character filenames, external URLs, generated files, and asset responses. ChangesHTML URL Encoding
Suggested reviewers: Priority: ➖ Normal Merge Risk: 🟡 Moderate · up to
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| Title check | |
The title clearly and specifically summarizes the main change: percent-encoding HTML output paths and serving assets under the encoded names. |
| Description check | |
The description provides detailed problem, fix, background, trade-offs, scope, verification steps, test coverage, and follow-up context. It does not use the template headings exactly, but it contains … |
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Inline comments:
In `@src/bundler/Chunk.rs`:
- Line 878: Update the count pass around cheap_normalizer so each path undergoes
platform_to_posix_in_place before cheap_prefix_normalizer, matching the write
pass’s separator normalization and keeping encoded length calculations
consistent. Add a regression case using a Windows backslash separator to verify
the count matches the encoded output.
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src/bun_core/string/immutable.rssrc/bundler/Chunk.rstest/bundler/bundler_html.test.ts
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I reviewed this and didn't find any bugs, but a human look is worthwhile: the change threads a length-affecting transform through the two-pass count/write buffer sizing in IntermediateOutput::code_with_source_map_shifts, and the encode set is meant to line up with #41615's route keys.
What was reviewed:
- Count pass and write pass both call
percent_encode_url_pathoncheap_normalizer[1], so the preallocatedtotal_lenmatches; over-count on Windows (write pass runsplatform_to_posix_in_place, count pass does not, so\counts as%5Cbut writes as/) only leaves slack —commit_spareusestotal_len - remain.len(), nottotal_len, so no uninitialized bytes leak. needs_escapematches the WHATWG path percent-encode set plus%/\;/and RFC 3986 sub-delims are left alone;cheap_normalizer[0](publicPath /./) is intentionally not encoded..iter().position(|&b| needs_escape(b))is a predicate, not a byte-literal equality, so thebyte-searchsource lint does not flag it.- Test fixture filenames (space,
#,%, parens, UTF-8) are all legal on NTFS; the externalcdn.example.comURL is only matched as text, never fetched.
Extended reasoning...
Overview
The PR adds strings::percent_encode_url_path (a Cow-returning helper that escapes the WHATWG URL path percent-encode set plus % and \) and applies it in src/bundler/Chunk.rs when the chunk being emitted is HTML, so that rewritten src/href values containing spaces, #, ?, %, or non-ASCII bytes still resolve to the emitted file. A new itBundled case in test/bundler/bundler_html.test.ts exercises four asset filenames covering each class and asserts the exact encoded URLs, that an external absolute URL is untouched, and that each encoded URL decodes to a file on disk.
Security risks
None identified. This is output serialization for build artifacts; the input is bundler-generated output filenames, not attacker-controlled data at runtime. Percent-encoding strictly narrows the byte set written into HTML attribute values, which is a hardening direction (e.g. " is now encoded).
Level of scrutiny
Moderate-to-high. The change sits inside a two-pass exact-count-then-write buffer allocation where a length mismatch would either panic (under-count) or trip a debug_assert!(remain.is_empty()) (over-count). I traced both passes: they call the identical helper on cheap_normalizer[1], so on POSIX the lengths are byte-identical. On Windows the write pass first runs platform_to_posix_in_place (turning \ into /) while the count pass does not, so a backslash would count as 3 bytes and write as 1 — but that is an over-count, and the tail commit uses total_len - remain.len() rather than total_len, so release builds emit correct output and only the debug assertion could fire. This was already flagged and ruled out this run. The PR also intentionally scopes to Content::Html only, deferring CSS url() to #41557 and leaving JS unchanged to match esbuild — a reasonable boundary, but the encode set is meant to be shared with #41615's Bun.serve route keys, which is a cross-PR coordination point a human should confirm.
Other factors
The new test is well-constructed: it uses itBundled, asserts exact encoded forms with toEqual on the full ordered array, verifies the round-trip new URL(url).pathname === url, and checks each decoded path exists on disk. Fixture filenames avoid Windows-invalid characters. The .iter().position(predicate) scan is not the byte-literal pattern the repo's source lint targets, and there is no obvious strings:: SIMD helper for a mixed range+set predicate. The double encoding (once per pass) is a minor cost but keeps the passes structurally symmetric.
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…der the encoded name too The bundled page now references each asset by its percent-encoded output name. Register the static route under that name (and keep the raw name for JS file-loader strings, which are emitted as is), in both the HTML-import path and the compiled HTML manifest path, and percent-encode the SourceMap header value the same way.
robobun
changed the title
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Ordering note from #41616 (the input side: it decodes |
…-url-percent-encoding
…ncode_url_path Both write a byte as is or as %XX with upper-case hex; they differ only in the byte set. percent_encode_except holds the loop, each caller passes its set. No change in output for either.
StaticRouteEntry::push_bundled_file adds a bundler output under its percent-encoded name and under its raw name. The HTML-import path and the compiled HTML manifest path both call it, and so does the page's own route, so every output file is reachable by the URL a browser requests for it. AnyRoute derives Clone (each variant holds a RefPtr, so a clone is another ref on the same route). That replaces the match on the route kind, which no longer compiled against main, where AnyRoute::FrameworkRouter is a unit variant. AnyServer::append_static_route and ServerConfig::append_static_route had no other caller and are gone.
The count pass uses the existing platform_to_posix_buf, which copies only on Windows, so JS and CSS chunks on POSIX take the same path as before. Both passes call one url_path binding in place of two copies of the if-HTML block.
| // HTML `src`/`href` values are URLs; JS and CSS strings stay raw. | ||
| let url_path: fn(&[u8]) -> Cow<'_, [u8]> = if matches!(chunk.content, Content::Html) | ||
| { | ||
| strings::percent_encode_url_path |
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🔴 Anyone who feeds a bun build HTML output back into Bun (bun ./dist/index.html, a Bun.serve import of the built page, a second bun build) now gets a Could not resolve error for any asset whose name has a space, #, % or non-ASCII byte, where the base resolved it. The page now carries ./my%20photo-<hash>.png (src/bundler/Chunk.rs:727), but HTMLScanner::create_import_record (src/bundler/HTMLScanner.rs:71) hands that attribute value to the resolver without percent-decoding, so the file lookup is for a name that is not on disk. Fix: decode the percent-encoded path before resolving an HTML src/href (the #41616 change) in the same release as this emitter change, so every URL this PR writes resolves again when Bun is the consumer.
Why this was flagged
A project with my photo.png referenced from index.html is built with bun build ./index.html --outdir dist; after this change dist/index.html contains <img src="./my%20photo-<hash>-png"> (src/bundler/Chunk.rs:727 selects strings::percent_encode_url_path for every Content::Html chunk). The user then runs bun ./dist/index.html, imports ./dist/index.html in Bun.serve, or bundles dist/index.html again. The scan pass creates the import record from the raw attribute bytes at src/bundler/HTMLScanner.rs:71-121 with no percent-decoding anywhere under src/bundler, so the resolver looks for dist/my%20photo-<hash>.png, which does not exist, and the build logs Could not resolve: "./my%20photo-<hash>.png" (src/bundler/bundle_v2.rs:2870) instead of serving the page. On the base branch the same output carried the raw name ./my photo-<hash>.png, which resolves. The PR description notes that #41616 adds the decoding on the input side; until that lands, nothing in this change lets Bun consume the HTML it now writes for these names.
Verification: Acknowledged in diff: the PR description notes #41616 percent-decodes before resolving, but nothing in this PR closes the gap. src/bundler/Chunk.rs:725-730 percent-encodes, so the emitted page carries ./my%20photo-<hash>.png; src/bundler/HTMLScanner.rs:71-123 never percent-decodes, so src/bundler/bundle_v2.rs:7014-7024 logs Could not resolve: "...". On the base, the raw bytes resolve, so this is a regression.
An automated safety screen replaced some characters, such as angle brackets, in the code quoted in this comment with HTML escape codes.
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Correct, and this PR cannot close it alone: the decode belongs to #41616, which rewrites create_import_record and is stacked on #43854. A second decoder here would conflict with it.
The two PRs are the two halves of one rule (decode src/href on input, encode on output). #41616 can land first without this regression, because its decoder does not change what main writes. So the order that has no window is #43854, then #41616, then this PR. After #41616 is in, this PR can also let its decoder accept %23, %25, %3F and %22 (it refuses them today because main cannot write them) and add a test that builds the built page again.
The PR description now says this on its first line. I am leaving this thread open until #41616 is on main.
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Inline comments:
Review comments at @src/bun_core/string/immutable.rs:
- Around line 2263-2267: Update the path-encoding predicate around
byte.is_ascii_graphic() to encode ampersands as %26 before inserting paths into
HTML attributes, keeping the encoded URL consistent with route registration.
- Line 2270: Replace the predicate-based byte search over path with
bun_core::strings searches for rejected ASCII and non-ASCII bytes, then select
the earliest match. Preserve Cow::Borrowed(path) when neither search finds a
rejected byte.
Review comments at @src/runtime/server/ServerConfig.rs:
- Line 232: Update the route-key generation around percent_encode_url_path so
raw and encoded manifest paths cannot register the same URL key. Ensure
colliding files remain reachable through distinct emitted URL paths; do not
retain aliases that recreate the collision.
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📒 Files selected for processing: 8
src/bun_core/string/immutable.rssrc/bundler/Chunk.rssrc/runtime/server/HTMLBundle.rssrc/runtime/server/ServerConfig.rssrc/runtime/server/mod.rssrc/runtime/server/server_body.rstest/bundler/bundler_html_server.test.tstest/js/bun/http/bun-serve-html.test.ts
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A rewritten src/href is spliced into a double-quoted attribute, so a browser reads `©-` in `cut©-<hash>.png` as a character reference. The HTML splice now writes the URL path with `&` as `&`. The URL itself keeps the `&`, so the request and the route key for such a name do not change. Tests: `cut©.png` in the three HTML tests, and a JS file-loader URL that is a valid percent-encoding (`a%20b.png`) keeps serving under its raw name.
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Beyond the inline findings, I checked the new & -> & rewrite added in the latest commit: the count pass and the write pass both go through the same html_attribute_url selected once per chunk in src/bundler/Chunk.rs, and the route key (push_bundled_file) and the SourceMap header use percent_encode_url_path directly, so the request line and the registered route both keep the raw & and still match.
Extended reasoning...
The latest commit addresses the & character-reference gap raised in an earlier run by wrapping the HTML-chunk path encoder in html_attribute_url; both measurement and emission use that one function pointer, and the server-side registration and header do not apply the HTML escaping, which is the correct split. The two remaining inline findings are pre-existing behaviors (:/* route-key prefixes and CSS url() names) not introduced by this diff.
Still open from earlier reviews (1):
- Unresolved: 1 blocking on lines changed since (possibly already fixed).
If you have decided not to act on one of these findings, resolve its thread (a reply alone leaves it open) and the next review stops counting it. To review this commit again now, use Re-run on its "Claude Code Review" check.
Land after #41616 or in the same release (Downsides).
Problem
bun build ./index.htmlwith<img src="./shot #1.png">writes<img src="./shot #1-6wrh68hc.png">. A browser ends the path at#and requests./shot%20.?,%and©break too.code_with_source_map_shifts(src/bundler/Chunk.rs) splices the raw output path into the attribute.Bun.serveregisters each output under the raw name, somy photo.pngis a 404.Fix
strings::percent_encode_url_path(what a browser escapes, plus%and\), with&as&.StaticRouteEntry::push_bundled_fileregisters each output of an HTML import or compiled manifest under that URL path and the raw name.Background
src/href. The linker replaces it with the output path.%26for&: it changes the request forQ&A.png. Considered only the encoded route key: a JSfileloader URL is sent raw.Downsides
Could not resolve: "./my%20photo-<hash>.png").Notes
html/percent-encodes-rewritten-urls(test/bundler/bundler_html.test.ts), "production build serves assets whose names need percent-encoding" (test/js/bun/http/bun-serve-html.test.ts),compile/{api,cli}/HTMLServerPercentEncodedAssets(test/bundler/bundler_html_server.test.ts). Names:my photo.png,shot #1.png,100%.png,ünï.png,cut©.png, a page namedmy page.html, anda%20b.pngthrough a JS import.<img src="./my%20photo-crx865yh.png"> <img src="./shot%20%231%3F-6wrh68hc.png">. The files on disk keep their names.Bun.serve({ routes: { "/": page }, development: false })on 1.4.3,my photo.png,shot #1.png,100%.pngandünï.pnggive 404, 404, 200, 404. With this change all four are 200. The page itself is also reachable by its own name (/my%20page.html), because its route goes through the same function.",#,%,<,>,?,\,^,`,{,}, DEL and every non-ASCII byte, upper-case hex./and every other ASCII byte are kept. For each byte in the WHATWG set a browser writes the same escape, so the request does not change for a name that works today.&stays in the URL and is written as&only in the attribute.cut©-<hash>.pngfollowed by-is a legacy character reference for a browser.%26would fix that too, but it would change the request line for every&name, and a server that maps the request path to a file without decoding would miss.[name]-[hash]names and theBun.serveHTML import uses the default templates. A JSfileloader URL for a file literally nameda%20b.pngkeeps its 200 because of the raw key (covered in the serve test).Bun.servescans each output path once at registration.percent_encode_uri_component(added on main by install: use the shared percent-encoding helpers in the yarn berry migration #45051) and the new function share one loop,percent_encode_except. They differ only in the byte set.encodeURIComponentitself is the wrong set here: it escapes/,@,+and&./_bun/asset/<hash>.<ext>and does not reach the splice. Standalone HTML (--compile --target=browser) inlines chunks anddata:URLs before the splice.url()(it needs the decode and the encode in one change, and has a false#fragmentdefect next to them) and a route key that starts with:(read as a route pattern). Both are present on main and are handed off as their own fixes.%23,%25,%3Fand%22and add a test that builds the built page again.sizetext 106,333,043 to 106,334,067 bytes (+1,024), data and bss equal, stripped file 106,505,992 bytes for both.bundler_html,bundler_html_server,standalone,html-import-manifest,bun-serve-html,bun-serve-static,bun-serve-routes,bun-serve-html-entry,bake/dev/html,bundler_splitting,esbuild/splitting,bundler_naming,cli/install/migration/yarn-berry, the source lints.