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…ed whole at EOF The decode budget from #43123 stopped at the end of the transport. `finalize_body_on_eof` decodes everything that is held, and a lot is held whenever the end arrives while the reader is behind: - Through a CONNECT tunnel, whose socket is never paused, all of the body and then the origin's close reach the client at once. A 256 MB-logical zstd or gzip body (270 KB on the wire) grew the client by 507 to 551 MB whether it ended by Content-Length, chunked or close; 1 GiB-logical by 1278 MB. - On a direct TLS connection the socket is paused, which defers a FIN but not a close_notify that came in with the body: 3 of 30 runs grew by 288 MB for a 64 MB-logical body. Now the end of the transport marks the body complete and decodes one budgeted pass like any other read. If input is still held, the client registers in `socketless_bodies` by `async_http_id` and stays alive without a socket. The consumer's pulls (`drain_queued_receive_resumes`) decode the rest a pass at a time through `send_progress_update_without_socket`, the socket-free update h2 and h3 already use, and an abort (`drain_queued_shutdowns`) fails it. The entry is removed by `unregister_abort_tracker`, which every terminal path runs before the client is freed. A tunnel whose inner TLS stream closes first keeps draining through its outer socket until the proxy closes that too. Also: the CONNECT test from #43123 never reached its proxy where the ambient NO_PROXY lists 127.0.0.1. The client env now drops the proxy variables and the test asserts that the proxy saw the CONNECT.
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Included review availability: Your plan provides up to 10 included reviews per hour; 5 remain after this review. WalkthroughThe HTTP client can return compressed response data for decoding after transport completion. FetchTasklet retains and decodes this data according to consumer demand. Tests cover framing, proxy tunnels, deferred errors, aborts, workers, secure responses, and connection reuse. ChangesHeld body decompression
Priority: ➖ Normal Merge Risk: ⚪ Minimal · up to No actionable issue remains in the supplied review evidence; the change is ready for normal merge checks. 🚥 Pre-merge checks | ✅ 4✅ Passed checks (4 passed)
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StatusReproduced on main (0ffd5b2, debug build with ASAN). The origin and the CONNECT proxy run in a separate node process.
The fix is in this PR: #43169. CI on 31132d6: the diff is green. The one red test is |
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the need for this hash map seems wrong? Can you come up with a way that makes this work by design instead?
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2 verified lower-impact observations (convention, logging or cleanup points) were not posted.
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src/http/lib.rs— nit: A maintainer reading the SAFETY invariant of from_erased_backref is told every stored NonNull lives in a holder the client outlives, which the new SOCKETLESS_BODIES static contradicts. The map at src/http/lib.rs:929 outlives every client; its entries are safe only because unregister_abort_tracker removes them before the client is freed. Fix: extend the INVARIANT list at src/http/lib.rs:851-858 to name socketless_bodies and state its removal-before-free rule, so the comment the unsafe block cites stays accurate.Extended reasoning...
src/http/lib.rs:1175 socketless_body() calls HTTPClient::from_erased_backref on a pointer taken from the SOCKETLESS_BODIES static map. The doc comment at lib.rs:851-858 says every NonNull reaching from_erased_backref is stored in an intrusive container (h2/h3 Stream.client, PendingConnect.waiters, ClientSession.pending_attach, socket ext slots) whose holder is strictly outlived by the HTTPClient's embedding AsyncHTTP. A process-lifetime static is the opposite: it outlives the client, and the guarantee that no dangling pointer is dereferenced comes from unregister_abort_tracker at lib.rs:1821-1823 running on every terminal path (fail at 4047, done at 4423, redirect at 4472, on_close at 2154). The unsafe block at lib.rs:866 cites this comment as its SAFETY argument, so the argument is now incomplete. Consequence: a future terminal path that skips unregister_abort_tracker would leave a dangling entry and the comment would not warn the author; the base branch had no such holder.
Verification: nit. Triggering condition: any maintainer reading the SAFETY justification for the
unsafeblock infrom_erased_backrefafter this change merges. Mechanism verified:/home/claude/bun/src/http/lib.rs:851-858(unchanged by the diff) states "INVARIANT: everyNonNull<HTTPClient<'static>>reaching here is a back-ref ... stored in an intrusive container (h2/h3Stream.client,… | nit.…
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Agreed. The map exists because the object that I kept alive is the HTTP client. A client without a socket has no owner and no address: every cross-thread message ( New shape, which I am building now: the rest of the body is a value, and the consumer owns it.
The same hand-off fits h2 and h3 at END_STREAM. I will keep that for a follow-up. If this is more than you want for this bug, the small alternative is no new map: the abort tracker value becomes an enum with a |
…consumer When every wire byte of a compressed body has arrived and the consumer's decode budget has left part of it undecoded, the request now ends as usual. The final result carries a HeldBody: the undecoded input and the decoder. FetchTasklet owns it and decodes one budget per reader pull in a work-pool job. No client outlives its socket, so the socketless registry is gone, and so are the special cases for a body that is complete but held.
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Updated 1:52 PM PT - Sep 24th, 2026
✅ @Jarred-Sumner, your commit 7d93c6e0e826f7b1ebd0a7baeb1b5c668b03cb39 passed in 🧪 To try this PR locally: bunx bun-pr 43169That installs a local version of the PR into your bun-43169 --bun |
robobun
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@Jarred-Sumner pushed in 0760886. The map is gone, and so is the client that outlived its socket.
Numbers for your 1 GiB gzip through CONNECT with a close: +1278 MB on main, +55 MB here (debug build with ASAN). The rest is in the PR body. The |
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Inline comments:
In `@src/http/lib.rs`:
- Around line 4093-4097: Update HTTPClient::decodes_on_demand so HTTP/1.1
responses with takes_held_body return true when the receive mode is either
demand-driven or BufferAll. Preserve the existing unlimited decompression cap in
the HeldBodyPass work-pool path.
In `@src/runtime/webcore/fetch/FetchTasklet.rs`:
- Line 2448: Remove the drive_held_body call from the
on_response_finalize/finalizer path so it never reads held_body or schedules JS
jobs during GC sweep; defer held-body processing to a non-finalizer execution
path instead, preserving abandon_response_body and abort_transport behavior.
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…le the wire is live The S3 download stream reads under the same backpressure signals as fetch, and takes no HeldBody. It keeps its per-pass budget until the last chunk. The last chunk is decoded in full for it, as a close did before.
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Beyond the inline finding, two other things were checked this round: the new is_body_abandoned discard in process_received_body (src/http/lib.rs:4112) is reached only from h1 call sites, so h2/h3 END_STREAM handling (still finalize_body_on_eof) is unchanged by it; and the S3 per-pass budget concern from the previous round is addressed in f8ef451 — decodes_on_demand no longer requires takes_held_body, and only the final chunk of a non-taker is uncapped.
Extended reasoning...
A confirmed use-after-free finding on the HeldBodyPass job under a stopped module-graph context is posted inline, and a CHANGES_REQUESTED review from a maintainer is outstanding, so approval is not on the table. This note only records what else was examined and ruled out in this run: the h1-only reach of the new abandoned-body discard (grep shows process_received_body is called solely from lib.rs h1 paths; h2/h3 ClientSession still call finalize_body_on_eof), and that the latest commit reworked decodes_on_demand/decompress_output_cap(is_final_chunk) so demand-driven consumers without takes_held_body (S3) keep the 256 KB per-pass budget on non-final chunks.
One verified lower-impact observation (a convention, logging or cleanup point) was not posted.
…xt too A decode pass whose context stopped is released unrun, and the end of an unread body was such a pass. The tasklet was then freed with the Response body still locked on it. The end of the body is now the tasklet's own task, which runs whatever became of the context, as the HTTP thread's last result does. A pass that is released unrun queues the same task.
…tion pointer A pass and the task that ends an unread body form &mut and can drop the last ref, so their pointer must not come from a &self. The append of a pass goes through handle_oom, like the HTTP thread's.
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I ran the tests of #43386 against this branch's
If that is intended (for example the body completes and the connection goes back to the pool), the case in #43386 needs a different expectation once this lands. If it is not, this may be a To reproduce: take bun bd test test/js/web/fetch/fetch-backpressure.test.ts -t 'its Response is collected: the fetch is aborted'Separately, both PRs rewrite |
…#43386) ### Problem - Since #43123, a gzip response body that inflates to between 512 KB and 32 MB costs 1.5 to 2.2x the client CPU (as reported) when it is read with `arrayBuffer()` or `text()`. - One exact-size libdeflate call used to inflate a body that arrived whole. It usually arrives before the caller has the `Response`, so the mode is still `Flowing`. `decompress_bytes` (`src/http/InternalState.rs`) budgets `Flowing` at 256 KB and runs zlib passes. ### Fix - `FetchTasklet` starts in a new receive mode, `Unclaimed`: no consumer has attached. It is demand-driven, like `Flowing`. - When such a body is complete and undecoded, `process_received_body` (`src/http/lib.rs`) moves `Unclaimed -> Paused` and decodes nothing. The consumer that attaches resumes the transport. `BufferAll` gets the libdeflate call, and a reader gets budgeted zlib passes. - Correct because one compare-and-swap from `Unclaimed` decides who was first. A held body is decoded only when a consumer attaches or its connection ends (Notes). - Verified: 23 new cases in `test/js/web/fetch/fetch-backpressure.test.ts`. The debug-log case fails on main with two zlib passes. The whole file passes. ### Background - `BodyReceiveMode` (`src/http/Signals.rs`) is the receive backpressure for a body handed to JS. Under `Flowing` and `Paused` the client decodes at most 256 KB per pass. `BufferAll` (`.text()`, `.arrayBuffer()`) never pauses. - libdeflate inflates a whole buffer into a whole buffer, so it cannot stop at a budget. zlib can, but is slower. - A gzip stream ends with ISIZE, the decoded size. It sizes the libdeflate output, up to 32 MB. <details><summary>Notes</summary> **#43169 rewrites the same function. Please read this before choosing a merge order.** #43169 (open) rewrites `process_received_body` and gives `decompress_output_cap` a parameter, so the two PRs conflict there. It does not fix this regression. I built its `src/` at 31132d6 under this PR's tests: the debug-log case still fails, with the libdeflate attempt followed by a zlib pass over the body. So both changes are needed, and the one that lands second has to carry the hold through the other's `process_received_body`. One more case of this PR, `held, and its Response is collected: the fetch is aborted`, times out after 5 s on that build, in 3 of 3 runs. It takes 0.5 s on main and here. The three collected-`Response` cases that main already has pass on that build, so this is specific to a body that is complete and held when the `Response` is collected. I do not know if that is an intended change in #43169 or a hang. The test helper edits (`serveConnectProxy` counts CONNECTs) are the same lines in both PRs. **Where the numbers come from.** Release builds of fd8422c (then main) with and without this diff, and of b52d513 (before #43123). This PR is the same diff on 367d939: it applied without changes, and none of the commits in between touch these hunks. I did not measure again after that rebase. Client CPU is `process.cpuUsage()` per request over keep-alive fetches of one gzip body. The origin is a separate process on other cores. The host is shared and ran at load 40 to 75. A 7-run median moved by about 13% between runs there, so only ratios inside one run are comparable. Median us CPU per request, 9 interleaved runs x 1000 requests, `arrayBuffer()`, before #43123 / main / this diff: ``` 524,288 B (control) 215 / 221 / 234 ranges overlap 786,432 B 316 / 419 / 286 1,048,576 B 431 / 534 / 381 1,572,864 B 552 / 751 / 547 4,194,304 B 1,904 / 2,315 / 1,949 ``` Main is 1.22 to 1.36x here. This diff is within noise of the cost before #43123 on every size in the band. The ratios below 1.00 are noise, not a speedup: this diff does two more thread hops per response than the old code. `text()` gives the same shape (1 MiB 569 / 704 / 570). So does an origin that sends the head a tick before the body (1 MiB 323 / 442 / 316), which is the path where the hold happens with no callback. A `res.body` reader costs the same as on main (1 MiB 629 / 585, 4 MiB 1,969 / 1,972). A 300 B keep-alive body, 15 runs x 3000 requests in two orders: 43 / 44 / 44 and 45 / 46 / 45. I did not use `bench/snippets/fetch-gzip.mjs`. It runs the server in the client process and reports wall time. On this host its unchanged rows moved by 20 to 27% between binaries, so it could not resolve the effect. **What the tests prove.** One case discriminates, and only in a debug build: it reads the `HTTPInternalState` debug log and expects one `Decompressing N bytes with libdeflate` line. On main it also sees `Decompressing 6167 bytes` and `Decompressing 4583 bytes`, the two zlib passes. From JavaScript the two paths deliver the same bytes by design, so nothing else can tell them apart. The other 22 cases pass on main too. They guard the new state: both framings, a buffered consumer and a reader, the body arriving with the head, after the head, and after the consumer, TLS, a CONNECT tunnel, an origin that closes the connection or the tunnel before a consumer attaches, a `Response` nobody reads (the process exits), and a collected `Response` (the fetch is aborted). The CONNECT proxy cases clear `NO_PROXY` and the proxy variables for the child and assert that the proxy saw one CONNECT. An ambient `NO_PROXY` that lists 127.0.0.1 makes `fetch()` ignore its `proxy` option, and the case then passes without a tunnel. I observed 0 CONNECTs that way and 1 with the variables cleared. **Please check this one.** `handle_response_body_from_multiple_packets` no longer sets `is_libdeflate_fast_path_disabled` after a pass over the final chunk. It sets it before a pass over a non-final chunk only. A held body needs the flag to stay clear so that the later pass can use libdeflate. I believe the rest is unchanged: `decompress_bytes` sets the flag itself when it enters the libdeflate block, and every later call sees a decoder that is not `None`. The chunked paths never set it after a final chunk. **At the end of the transport.** The first version of this description said that nothing is decoded for a `Response` that nobody reads. That is true only while the connection is open. A review pointed out that `finalize_body_on_eof` decodes whatever is held with no budget, and a held body reaches it whole. Through a CONNECT tunnel the socket is never paused, so an origin that closes an idle connection gets there before any consumer. I confirmed it: a `res.body` reader whose tunnel closed first got its body from one `Decompressing 6167 bytes with libdeflate` call. Main has the same gap for the part of a body it has not decoded yet (#43123 lists it as still unbounded), and the hold never decodes more than main does. It does not close the gap. #43169 is the change that bounds it, so I did not copy that work here. The four close cases assert exact bytes, not memory. **What the hold costs.** A reader of a held body gets its first chunk one thread round trip later. A held body that nobody reads keeps its connection with nothing decoded, where main keeps it with 256 KB decoded. For a gzip stream with a truthful trailer, the set of bodies is a subset of what #43123 already parks (a decoded size of 256 KB or more). The hold trusts the trailer. A stream whose trailer overstates its size is held too, where main would decode it and free the connection. That gives a server nothing new: it can already make a client park a connection with a real body of that size, which is a few KB on the wire. **Unchanged.** Bodies up to 512 KB, deflate, brotli and zstd, HTTP/2 and HTTP/3 (they start `Unclaimed` but are never held, because their output cap is unbounded), S3 (its `Store` still starts `Flowing`), and any body that arrives in more than one read. </details> --------- Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
… its consumer main's #43386 held such a body in the HTTP client (Unclaimed -> Paused) until a consumer attached. Here the request ends and the body goes to the consumer as a HeldBody, so that hold is gone: - process_received_body decodes nothing of it while no consumer has attached. - HeldBody::decode inflates it in one exact-size libdeflate call for a consumer that takes the whole body. A reader gets budgeted zlib passes. - FetchTasklet decodes nothing of a held body until a consumer attaches. - Signals::hold_for_consumer is removed. The test of a collected Response with a held body expected the origin to see its connection close. The request has ended by then and the connection is back in the pool, so the test now counts the freed tasklets and the decode passes.
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- 🪄 Fix CodeRabbit comments on this PR
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Inline comments:
In `@src/runtime/webcore/fetch/FetchTasklet.rs`:
- Around line 1926-1931: Update the merge logic for scheduled_response_buffer in
FetchTasklet so that when pass.out is larger than the buffered prefix, move
pass.out into the output and prepend the existing buffered bytes. Keep the
current assignment for an empty buffer and retain the existing write path when
the buffer is not smaller.
In `@test/js/web/fetch/fetch-backpressure.test.ts`:
- Line 1298: Update the spawned client’s environment in the fetch backpressure
test to use clientEnv instead of bunEnv, ensuring proxy variables are excluded;
if clientEnv is not in scope for this describe block, move its definition to the
shared scope.
- Around line 1305-1316: Add a separate test case in the fetch backpressure test
that consumes a compressed response and asserts the `passes` collected by the
`scan` helper are non-empty, confirming decompression logging is active. Keep
the existing collected-response assertion that expects `passes: []` unchanged.
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…f copying it When .text() takes the rest of a held body, the decoded output can be far larger than the bytes already buffered. Copying it onto the buffer doubled peak memory. The buffered bytes now go in front of the output, and the output becomes the buffer. The collected-Response test now runs its client without proxy variables, and its GC loop is bounded so that a tasklet that is never freed fails the count.
The debug-log tests in fetch-backpressure.test.ts count decode passes. A zlib pass over a held body wrote no log line, so a fallback from the one libdeflate call to zlib was invisible to them.
The collected-Response case asserts that no pass is logged while the bodies are held. After they are freed, the client now reads one more body, and the test expects exactly one pass from it.
A held body is the undecoded rest of a response whose transport is done. Its consumer decodes it in work-pool jobs, and the first job starts pool threads. That is not worth it for a short rest. - With the last of a body, the HTTP thread decodes up to 64 KB more than the budget. A body that ends inside that leaves no held body. - A paused consumer gets the same 64 KB with the last of a body. - A zlib pass over a held body is tagged in the debug log, so a test can tell it from a pass on the HTTP thread.
Three comments still said that the HTTP client keeps a complete body and that the consumer resumes it. The Response keeps the body now. No code change.
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Problem
fetch()body decodes ahead of its reader, but not when the transport ends:finalize_body_on_eof(src/http/InternalState.rs) decodes everything that is held. Through a CONNECT tunnel, a 256 MB gzip body whose origin closes grows the client by 507 to 551 MB.close_notifyin one read does the same: 3 of 30 runs grew 288 MB.Fix
HeldBody: the undecoded input and decoder (to_result,src/http/lib.rs).FetchTaskletowns it. Each reader pull decodes one pass in a work-poolJob(drive_held_body), and.text()decodes the rest in one. An abort, a cancel, or a collected Response drops it.Signals::hold_for_consumeris gone. Nothing outlives its socket, so there is no registry.test/js/web/fetch/fetch-backpressure.test.ts(five new cases fail on main). Also the fetch compression, abort, h2, h3 and proxy suites.Background
InternalState::compressed_body.Options::takes_held_bodygets aHeldBody. The S3 download stream does not: its last chunk is decoded in full.bun_jsc::Jobruns on the work pool and completes on the JS thread. A VM that stops waits for it, then drops it unrun.Notes
Measured (debug build with ASAN, origin and proxy in a node process, reader takes 16 chunks 100 ms apart, 256 MB is 270 KB on the wire):
.bytes()over a 512 MB zstd body with one budget already buffered (6b5d6da): peak RSS (VmHWM) grows by 1029 MB when the pass is copied onto the buffer, and by 802 MB now that the pass becomes the buffer.A rest that is short ends on the HTTP thread (985938d): with the last of a body it decodes up to 64 KB more than the budget (
HELD_BODY_MIN), so such a body needs no work-pool job. A paused consumer gets the same 64 KB.Every byte still arrives.
.bytes(). 9 of 9 exact. Keep-alive: 2 of 2..bytes(). All exact.await (await fetch(url)).text()racing the first pass: 600 of 600 in a debug build.What each end of a held body does.
ZlibError, after the eight good budgets before it.AbortSignal: the pending read, or a later.text(), rejects withAbortError.FetchTaskletdebug log).Bun.ModuleGraphthat fetched it:dispose()ends its body withAbortError. The end of an unread body is the tasklet's own task (ContextId::NONE), so it runs in a stopped context too and settles the body before the tasklet is freed.Also in this PR.
process_received_body). It was a pre-existing spike on the path from fetch: bound decompressed output to reader demand #43123.NO_PROXYlists 127.0.0.1. The client now runs without proxy variables, and the test asserts that the proxy saw one CONNECT.Not in this PR. h2 and h3 still decode what arrives. The same hand-off fits them at END_STREAM. The S3 download task takes no
HeldBodyyet, so what one socket read left undecoded when the wire completes is decoded at once for it. S3 streams and.bytes()of an 8 MB object are exact for gzip, br and zstd with Content-Length, chunked and close-delimited framing (9 of 9), andgzip from S3: a reader that takes a little holds a littlecovers its budget.Local runs that fail the same way on main's
src/(slow debug build, no IPv6, root user):fetch-tcp-stress, one case offetch-leak, some cases offetch.test.tsandfetch.stream.test.ts.no test proof · iteration 5 · platform-specific test(s) that do not run on this machine, deferring to CI, which covers all platforms: test/js/web/fetch/fetch-backpressure.test.ts