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Status: reproduced on a release build of main with a raw HTTP/1.1 client against a fetch handler. |
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ChangesFile Slice Response Framing
Suggested reviewers: Priority: ➖ Normal Merge Risk: ⚪ Minimal · up to
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Check skipped because no linked issues were found for this pull request. |
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Check skipped because no linked issues were found for this pull request. |
| Title check | |
The title clearly and concisely describes the primary change: deriving Content-Length from the file window being streamed. |
| Description check | |
The description explains the problem, fix, verification steps, test results, limitations, and related work. It uses Problem and Fix sections instead of the template headings, but it provides the requi… |
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Inline comments:
Review comments at @test/js/bun/http/bun-serve-file.test.ts:
- Around line 1381-1412: Update wireResponse to check whether the response-head
delimiter was received before parsing status, headers, or body; if missing,
throw a clear error that includes the captured raw response.
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src/runtime/server/RequestContext.rstest/js/bun/http/bun-serve-file.test.ts
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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 switching render_metadata from blob.size() to sendfile.remain changes any other response: needs_content_length is only set true at RequestContext.rs:1900 (regular files, right before remain is clamped at :1911-1918), cleared at :2549, and left false for FIFOs/char devices, so no other caller's Content-Length moves.
Extended reasoning...
The Rust change is a two-hunk edit to render_metadata in src/runtime/server/RequestContext.rs that makes Content-Length always come from the clamped sendfile window; the test file adds a shared raw-socket helper and three framing tests. No auth, crypto, or input-parsing surface is touched. The inline findings (helper resolving on error, a pinned 206-for-404 row, and the pre-existing fd-offset, HEAD, TRACE, and 200-without-Content-Range siblings) already signal a human should weigh the stacked status PR; this note only records the setter audit that was ruled out.
Additional findings (outside the current diff — GitHub can't attach inline comments there):
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🟣
src/runtime/server/RequestContext.rs— Clients that probe with HEAD before GET now get two different Content-Length values for the same slice once the file has shrunk. GET takes the clampedsendfile.remainat RequestContext.rs:3890, but HEAD at RequestContext.rs:2671-2678 still writes the Blob's cached size, whichresolve_sizeonly re-stats whenseekableis unset (Blob.rs:2132). On base both said the stale number, so a HEAD-then-GET client saw one length. Fix: size HEAD from the same clamp GET uses (re-stat indo_render_head_responseor route HEAD throughdo_sendfile), covering path and fd slices; the PR's own test exempts this row at test:1584.Why this was flagged
A long-lived server keeps a Bun.file whose
.sizewas read (setsseekable), returnsfile.slice(a)from a fetch handler, and the file is later truncated. GET goes through do_sendfile:b.size.set(stat_size)at RequestContext.rs:1893, remain clamped at :1911-1918, Content-Length written from remain at :3890 (6 in the test fixture). HEAD goes through do_render_head_response:blob.resolve_size()at :2671 skips the fstat becauseseekable.is_some()(Blob.rs:2132-2133) and writes the cached window (11) at :2678. On base GET wroteblob.size()= stat_size = 11 too, so HEAD and GET agreed. After merge a cache or download manager that validates with HEAD and then ranges or resumes with GET sees 11 vs 6 and treats the resource as changed or truncated on every request until restart. The REVIEW.md same-class rule names this sibling site; the PR defers it to #41585 but ships a test comment (test:1584) acknowledging the mismatch. Remedy: write HEAD's Content-Length from the same stat-and-clamp as GET.Verification: pre-existing; acknowledged in diff: the PR description lists "HEAD sizes from a cached stat" under "Not fixed here" and the test pins it at test/js/bun/http/bun-serve-file.test.ts:1584. HEAD sizes from
blob.size.get()(RequestContext.rs:2671-2678);resolve_sizeonly callsresolve_file_statwhenseekable.is_none()(Blob.rs:2132-2133). The HEAD value (11) is identical on base. -
🟣
src/runtime/server/RequestContext.rs— A TRACE request for a file response still leaves a keep-alive connection out of step, the same symptom this PR fixes for GET. At RequestContext.rs:1991 render_metadata writesContent-Length: remain(the slice length), then :1994!self.method.has_body()ends the response with zero bytes at :2002. The next request on that connection is read as the owed body, as the PR's own pipelining test shows for GET. Fix: when the method has no body, zeroremainbeforerender_metadata(or close the connection) so the declared length matches the 0 bytes sent, for TRACE and any future HEAD routed throughdo_sendfile.Why this was flagged
Method::has_body (src/http_types/Method.rs:176-178) is false for HEAD and TRACE. HEAD is diverted earlier, but TRACE of a route that returns
Bun.file(path)or a slice reaches do_sendfile.set_needs_content_length(is_regular)at :1900 is true, render_metadata at :1991 writescontent-lengthfromsendfile.remain(:3890), then :1994 takes the no-body branch and callsresp.end(b"", close)at :2002 withclosefromshould_close_connection(), which keeps the connection open for HTTP/1.1 keep-alive. The peer now owes N bytes it never gets; a proxy or client reusing the connection parses the next response head as body, the exact failure the PR description reports for GET (curl 'end of response with N bytes missing'). Base wroteblob.size()and had the same bug, but the PR's stated goal is framing from bytes sent, and the no-body branch still declares a length it does not send. Population: any public Bun.serve exposed to scanners that issue TRACE (common in security probes). Remedy: set remain to 0 (or force close) on the!has_body()path before rendering metadata.Verification: pre-existing; acknowledged in diff: the PR description's Limits section cites #19615 for TRACE of a file body, on main and with this PR. Trigger: an HTTP/1.1 keep-alive TRACE request to a fetch handler that returns
Bun.file(path). src/runtime/server/RequestContext.rs:1991render_metadatawritescontent-lengthassendfile.remain; then :1994!self.method.has_body()takes the no-body branch and :2002resp.end(b"", close).
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| if self.flags.needs_content_length() { | ||
| resp.write_header_int(b"content-length", size as u64); | ||
| resp.write_header_int(b"content-length", sendfile.remain as u64); |
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🟣 pre-existing, not blocking: pre-existing: a Bun.file(fd) response whose window starts at byte 0 still declares more bytes than it sends when the descriptor's position is not 0, so clients still hang or read the next response out of step. The header at src/runtime/server/RequestContext.rs:3890 now promises sendfile.remain bytes (clamped from the stat'd size), but the reader path only positions the fd when offset > 0 (src/runtime/server/FileResponseStream.rs:245-249), so reader.start reads from wherever the descriptor is. Fix: for regular files read every window with pread from sendfile.offset, including offset 0 (always start_file_offset), so the bytes sent match the declared length on both the reader and sendfile paths.
A small fix can ride a push you are already making; otherwise a short reply is enough.
Why this was flagged
A handler returns new Response(Bun.file(fd)) or Bun.file(fd).slice(0, n) for a regular file whose descriptor position is not 0 (a prior read, or a shared fd reused across requests). do_sendfile stats the file and sets sendfile.remain to the window clamped against st_size (RequestContext.rs:1911-1918) and render_metadata writes Content-Length: remain (RequestContext.rs:3890). FileResponseStream::start passes offset: 0, and at FileResponseStream.rs:245-249 it calls reader.start(fd, pollable) instead of start_file_offset, so the BufferedReader uses plain read(2) from the current position (PipeReader.rs:576-579 only sets USE_PREAD in start_file_offset). The reader hits EOF after st_size - position bytes and ends the response short of the declared length. On the base branch the header was the full file size and the body was the same short read, so the response was mis-framed there too; the PR fixes the header for offsets > 0 and for fd slices but this input class stays out of step.
Verification: src/runtime/server/RequestContext.rs:1901-1918 computes sendfile.remain purely from the stat'd size and the blob window, never from the fd position. src/runtime/server/FileResponseStream.rs:245-249 calls reader.start(opts.fd, pollable) when opts.offset == 0, and only start_file_offset sets USE_PREAD. On the base commit the same route fails identically for a whole Bun.file(fd).
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Confirmed, and this PR does not change it. One descriptor that serves slice(0, 4) three times sends 0123, 4567, 89AB on main and here. #33873 had the change (pread for a regular file at offset 0) and was closed as stale. It is being revived as a separate PR.
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@robobun rebase |
…w it streams `render_metadata` took the length from the blob size unless the `needs_content_range` bit was set. `do_sendfile` sets the blob size to the file size. It sets the bit from the slice length before the clamp, and never for a file descriptor. So a slice as long as the file that starts past byte 0, and every slice of `Bun.file(fd)`, declared the whole file and sent the window. The connection stays open after the short body. `render_metadata` now writes `sendfile.remain`, the length that `do_sendfile` gives to `FileResponseStream`. No status changes.
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Rebased onto e655c58 (now 4bdf0f8). The conflict was in The push also takes three review notes. On the two findings outside the diff: HEAD takes its length from the cached stat (#41585 routes HEAD through |
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I reviewed the new push and found no bugs; the two nits from my earlier pass (the shared helper's error() now rejects, and the explicit-status row moved to the framing-only group) are addressed. A maintainer look is still worthwhile only for the design point the PR itself flags: slice(5, 21) now answers a cleanly framed 200 with no Content-Range, with the status question left to the stacked PR.
What was reviewed:
- Traced the one-line change in
render_metadata:needs_content_lengthis set only indo_sendfile(RequestContext.rs:1900) afterSendfileContextis clamped to the stat'd size, the Range branch rewritesremainbeforerender_metadata_corkedruns, anddo_render_head_responseclears the flag, sosendfile.remainis always populated when the header is written. - Checked the tests fail on main for the right reason:
path slice(5, 21)declared 16 and sent 11 before, and the Linux sendfile variant covers the 1 MiB reader/sendfile boundary on both path and fd windows. - Confirmed the hoisted
wireResponsehelper preserves the original file-route test's assertions (samecontentLength/bodyfields).
Extended reasoning...
The diff is a one-line change in src/runtime/server/RequestContext.rs that writes Content-Length from the clamped sendfile window instead of the blob size, plus ~300 lines of new tests in test/js/bun/http/bun-serve-file.test.ts covering path/fd slices, GET/HEAD, TLS, keep-alive framing, and the Linux sendfile path. It touches HTTP response framing (a request-desync-adjacent surface) and the change makes framing stricter, not laxer; no auth, crypto, or permission code is involved. The Rust change was traced end to end and the prior inline feedback was addressed in the new commit, but the PR deliberately leaves a user-visible status/Content-Range decision to a stacked PR and a maintainer commented before the latest push, so a human decision on that semantic point is the reason for defer rather than approve.
Still open from earlier reviews (1):
- Unresolved: 1 minor or pre-existing.
Problem
Bun.file()slice can declare more bytes than it sends.slice(5, 21)of a 16-byte file answersContent-Length: 16with 11 bytes. EveryBun.file(fd)slice declares the whole file. curl waits 12 s, then fails withend of response with 5 bytes missing. A relay that reuses the connection reads the next response as those bytes.render_metadata(src/runtime/server/RequestContext.rs:3797) took the length from the blob size (the file size) unless theneeds_content_rangebit was set.do_sendfile(:1906) sets that bit before it clamps the slice, and never for an fd.Fix
render_metadatawritesContent-Lengthfromsendfile.remain, the length thatdo_sendfilegives the stream.Content-Rangedo not change (probes in Notes).test/js/bun/http/bun-serve-file.test.tsfail on main by assertion. Also ran that file andserve.test.tsin full.Background
SendfileContext { offset, remain, total }is the byte window of a file response.FileResponseStreamsendsremainbytes fromoffset.Downsides
slice(5, 21)now answers a framed200with noContent-Range. A client of the documentedRangehandler takes those 11 bytes for the whole file. Bun.serve: answer 206 for a Bun.file() slice as long as the file that starts past byte 0 #44827 decides the status.Notes
Found by a fuzzer that checks the bytes of
Bun.servefile responses. No user has reported it.Who reaches it. The handler in
docs/runtime/http/routing.mdx("To send part of a file") returnsnew Response(bigFile.slice(start, end))from theRangeheader.Range: bytes=100-307300on a 307200-byte file (end minus start equal to the file size, start above 0) gets200,Content-Length: 307200and 307100 bytes on main. Other reaches of the same line: everyBun.file(fd)slice, a slice of a sized file that then shrinks to the stored length of the slice, and a sizedBun.file(fd)whose file grows.What a client sees on main (documented handler, 16-byte file,
Range: bytes=5-21). curl:curl: (18) end of response with 5 bytes missingafter 12,056 ms. The controlbytes=5-20answers in 237 ms. A raw client that sends a second request on the connection after the 11 bytes reads56789ABCDEFHTTP/as the body. With this PR curl exits 0.Observed, debug builds of 620b50f.
Content-RangechangedThe matrix row that stays mis-framed is
Bun.file(fd).slice(0, 100)after an earlier read of that descriptor:Content-Length: 100, 0 bytes (main:307200, 0 bytes). See the limits.History per transport (documented handler,
Range: bytes=100-307300, official release binaries).200, length 307200, 307100 bytes206, length 307100,bytes 100-307199/*200, length 307200, 307100 bytes200, length 307200, 307100 bytes200, length 307100200, length 307100The first tag that has #29202 is bun-v1.3.13. The bit and its use for the length date from 0617896 (first tag bun-v0.3.0). Also measured: plain HTTP mis-frames on v1.0.0 and v1.3.0, and TLS is right on v1.3.0. Windows and macOS were not run.
Limits that this PR does not change.
slice(0, 4)served three times sends0123,4567,89ABon main and with this PR. The header is now 4. The bytes come from the position of the descriptor (FileResponseStream::startcallsstart_file_offsetonly for an offset above 0).slice(4, 8)is right. The tests give each fd window its own descriptor and an offset above 0. Bun.file(fd): use pread so bytes match fstat-derived size #33873 had a fix and was closed as stale. Bun.serve: read a Bun.file(fd) body at its offset, not at the descriptor's position #45266 now reads such a body at its offset. Land Bun.serve: read a Bun.file(fd) body at its offset, not at the descriptor's position #45266 before this PR or together with it: this PR alone turns an fd slice at byte 0 from a failed response into a well-framed one with the wrong bytes (Content-Length: 4over4567). The test helperwireResponseis the same in both PRs, byte for byte. The PR that lands second adds theContent-Lengthassertion for aBun.file(fd)slice at byte 0.do_render_head_responsesizes the blob from its cached stat. Sized file of 1000 bytes,slice(100, 1000), then truncate to 900: main GET 900 (800 bytes sent), HEAD 900. This PR GET 800, HEAD 900. Bun.serve: resolve a file body for HEAD the same way as for GET #41585 routes HEAD throughdo_sendfile.200,content-length: 16, 0 bytes, on main and with this PR.do_sendfileends a method without a body after the head. TRACE body not sent #19615.Content-Lengthheader: Bun.serve: drop Transfer-Encoding and Content-Length from a Bun.file() route's Response headers #43108. A stream that ends short of its length: Close the connection when a Bun.file response ends short of its Content-Length #41622.Cost for other responses. None added, and one removed. On main
render_metadatacallsblob.size()for every response and uses the result only for a file. For a GET whose body is an ASCII string that call is a UTF-8 length pass over the body. Release builds of 620b50f and of this PR, gdbstepifrom entry to return ofrender_metadata, two runs each with equal counts:Code bytes (
nm -S,size, the same builds):render_metadata2385 and 2422 to 2321 and 2334 (2 bodies),do_sendfile4571 unchanged (8 bodies), text of the stripped binary 88,977,421 to 88,976,769. Syscalls: 2pread64per path-plus-fd response pair before and after (gdbcatch syscallon debug builds,straceis not available in this environment).Tests (
bun-serve-file.test.ts).a fetch handler frames a Bun.file() slice by the bytes it serves: 18 windows over a raw socket, GET and HEAD, the shrink case, and one window over TLS. For a path slice as long as the file that starts past byte 0, and for a slice with an explicit status, it asserts the framing only. The status of the other rows is pinned.a Range as long as the file, past byte 0, leaves the next response on the connection in step: the documented handler, two requests on one connection.a fetch handler frames a Bun.file() slice that goes through sendfile(Linux): a file of 1 MiB + 100 bytes. Three windows of 1 MiB take sendfile(2), one of 1 MiB - 1 takes the reader.bun-serve-file.test.ts(179): 174 pass. The one failure is apollabletest that times out on main too.serve.test.ts(330): 326 pass. The 3 failures are on main too: the root-port test (the machine runs as root) and two timeouts (abort a sendfile response,--hot reload of a node:http server).Other PRs. This PR should land before #41585: by a reading of its diff, without this PR it makes HEAD of a path slice as long as the file declare the file size. With it, the line that #41585 adds for an fd (
b.size.set(sendfile.remain)) is not needed. The status hunk of draft #43910 is in #44827.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/http/bun-serve-file.test.ts