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…nsumed formData() lifted the payload out of an unread .body stream to find the body's own Content-Type, and a static or file route did the same to get the bytes it serves. Since #42516 that lift closes and locks the stream. When the body was then not consumed (a Content-Type that is not form data, a Response that stays reusable as a route), the program's stream was left locked while bodyUsed stayed false, and Bun.write() refused the Response as already used. formData() now decides the type before the lift, and a route shares the payload with the stream instead of taking it.
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Updated 9:40 AM PT - Oct 11th, 2026
✅ @robobun, your commit 879a7aa0e139dfbafcc3f82e76d9f5b3e0fcca35 passed in 🧪 To try this PR locally: bunx bun-pr 44930That installs a local version of the PR into your bun-44930 --bun |
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Reproduced on the released 1.4.3 line with two reduced programs, each run on that build and on this branch:
Test: This PR is limited to |
- Remove the formData() reorder, Value::blob_content_type and the get_content_type hunks. formData() is as on main. - FileRoute::from_js refuses a file descriptor from the peeked Blob, before any lift. It decides whether a second reader would compete for the file with store_yields_bytes_once, which does not stat into the shared store. - Tests: a fetched Response as a route, a refused Bun.file(fd) route, and Bun.file().size after a route over its stream.
…-at-body-without-spending-stream
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robobun
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No actionable comments were generated in the recent review. 🎉 ℹ️ Recent review info
WalkthroughUnread response streams can expose reusable blobs to file and static route construction without consuming the original body. File routes retain a duplicate and initialize from response headers and status. Tests cover route delivery and body preservation across several response types. ChangesResponse body route construction
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The title clearly and concisely describes the main change: sharing a route payload with an unread Response body stream. |
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The description explains the problem, implementation, scope, trade-offs, and verification results. It does not use the exact template headings, but it provides the required information and is sufficie… |
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Explanation
The description explains the problem, implementation, scope, trade-offs, and verification results. It does not use the exact template headings, but it provides the required information and is sufficiently complete.
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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 test note, I also checked the FileRoute::init restructure for behavior drift on the lift path (fd refusal still precedes use_(), and global_this.set now runs on both the peeked and lifted Blob), and whether store_yields_bytes_once writes a stat into the store the program's Bun.file() shares (it caches mode_seen_by_clone separately, so file.size is unaffected). The open design question in the description — whether the stream taken from .body should stay the body after a route looks at it — is a call for a maintainer, so a human look is still worthwhile.
Extended reasoning...
The change adds a non-consuming peek path through Body.rs, ReadableStream.rs, ByteBlobLoader.rs and ByteStream.rs and rewires StaticRoute/FileRoute init to share a Response's payload with an already-obtained but unread .body stream instead of lifting it; it touches no auth, crypto or injection surface. It is not approvable automatically because it changes observable body/stream semantics across four webcore sources, the author explicitly leaves a design question open, one verified finding is being withheld from the posted review, and the only applicable earlier bot thread was self-resolved by the author.
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Inline comments:
Review comments at @test/js/bun/http/bun-serve-static.test.ts:
- Line 442: Remove the local deadline and timeout check from the
serveOnceArrived polling logic so slow buffering can complete; rely on Bun’s
test timeout to bound a stuck poll.
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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 nit, I also checked the raw loader deref in ReadableStream::peek_blob (same stream-alive lifetime as the existing to_any_blob arm, read-only) and the store sharing (self.store.clone()? in ByteBlobLoader::peek_blob is a balanced RefPtr clone, the loader keeps its store), and confirmed FileRoute::serve now refuses an fd before any lift on both branches. The bounded poll from the earlier round is in place.
Extended reasoning...
The change replaces the destructive to_blob_if_possible() lift in StaticRoute and FileRoute with a non-destructive peek_blob over the Blob/File/Bytes/JS stream sources, sharing the underlying store with the program's .body stream; it touches no auth or injection surface. The only finding this round is a test-coverage nit, and the prior nit was addressed by d685979, but the design question the author raised for a maintainer (share versus lift-and-repoint) and the shared-store semantics still warrant a human look.
Problem
const s = r.bodyon a Responser,Bun.serve({ routes: { "/a": r } })leavesslocked whiler.bodyUsedis false.s.getReader()throwsReadableStream is locked.Bun.write(path, r)fails withERR_BODY_ALREADY_USED. So does aBun.file()body (1.4.2 read the file).StaticRoute::from_jsandFileRoute::from_jscallto_blob_if_possible()to look at the payload. Since Close a body's stream when a consumer takes its payload without reading it #42516 that lift closes and locks the stream, and a route never reads it.Fix
ReadableStream::peek_blobreturns a Blob over the same store and takes nothing out.FileRouterefuses a file descriptor before any lift.test/js/bun/http/bun-serve-static.test.ts(29 new cases, 27 fail on main).Background
.bodymakes a bodyLocked: its payload sits behind a native stream. A lift takes the payload out as a Blob and spends the stream..body, asclone()does: the stream the program holds stays spent.Downsides
.bodywas read copies the received bytes once.size).formData()(formData(): check the Content-Type before the lift that spends the .body stream #44999) and in a handler's 204 or 304 Response.Notes
.bodywas read (string,HEAD,Uint8Array): the stream is locked whilebodyUsedis false in 3 of 3 cases on 1.4.3, in 0 of 3 here.const r = new Response(Bun.file(p)), s = r.body, thenras a route and one GET, then five uses (reads,s.tee(),new Response(s).text(),Bun.write(path, r),r.text()): 4 of 5 are refused on 1.4.3, all 5 give the whole file here. The same holds for a string body.peek_blobmirrorsto_any_blobsource by source. A Blob store and a lazy file store are shared by reference. A fully received network body is copied. A closed unread JS stream is the empty Blob. Anything else is not peeked, and the route lifts or refuses as before.FileRoutedecides "a second reader would compete" withstore_yields_bytes_once. It does not stat into the store that the program'sBun.file()answers from, sofile.sizekeeps following the file..bodystay the body after the look (this PR)? The other design lifts and then re-points.body(about 15 lines, and it covers every look site), but the stream the program holds stays spent.text/plainfor a string body whose.bodywas read. It readswas_stringafter the lift inStaticRoute::from_js, and this PR removes that lift. Whichever lands second takeswas_stringfrom the loader at the peek.from_jsfunctions. The conflict is textual.formData()with a Content-Type that is not form data (get_form_datainsrc/runtime/webcore/Body.rs). formData(): check the Content-Type before the lift that spends the .body stream #44999 fixes it with no behaviour change. formData(): read the body before the MIME type check rejects #44969 proposes Fetch's end state (the body is used up), which is breaking.src/runtime/server/RequestContext.rs:2582) andprotect_for_body_and_render(:4035). On 1.4.3 aGETanswered with status 204 or 304 leaves{"locked":true,"bodyUsed":false}. Neither Bun.serve: do not end a body stream that a reader holds, and refuse it on HEAD as on GET #43973 nor Bun.serve: resolve a file body for HEAD the same way as for GET #41585 removes that lift. It is reported separately.Bun.file().sizethrough a stat into the shared store (fixed), the fd refusal came after the lift (fixed), aformData()end state and a widerget_content_typewere in this PR (removed), the overlapping PRs were not named (named above), the HEAD site was said to be covered by Bun.serve: do not end a body stream that a reader holds, and refuse it on HEAD as on GET #43973 (corrected above). Open: the question above.bun-serve-static,bun-serve-static-stress-access-body,bun-serve-static-stress-no-body,bun-serve-file,bun-serve-routes,bun-serve-headers,serve-reused-response,serve-file-slice-read-error,bun-server,body,body-clone. Failures seen were 5 s timeouts on the debug build in tests that do not use routes:bun-serve-file.test.ts"pollable Bun.file(path) ... resumes when the client reads",bun-server.test.ts"server.stop() drain promise" (12 concurrent child processes, each passes alone),body.test.ts"string body consumption does not leak".