[FlightReply] Don't drop FormData entries in decodeReplyFromBusboy#36468
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could store queueFields on the file entry. always push to the top pendingFile.
Then you only flush when you get data an end even on value and you flush each file followed by it's queueFields until you hit the next pending file. splice the files array to eliminate flushed files and fields
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Fixes a regression from facebook#36425 where referenced `FormData` entries can be dropped by `decodeReplyFromBusboy` when files are interleaved with text fields in the payload. `decodeReplyFromBusboy` queues text fields that arrive while a file is being streamed and flushes them after the last file's `'end'`, working around busboy emitting `'end'` deferred relative to subsequent `'field'` events. With multiple files interleaved with text, this loses the relative order of the affected text entries. The reorder was a long-standing but invisible issue — entries came back in the wrong order but were all present — until facebook#36425 tightened how referenced FormData entries are collected from the backing store to rely on them being contiguous. With that assumption violated, referenced FormDatas can now come back with some entries dropped. The pattern is most easily surfaced through `useActionState` actions that return the submitted `FormData` as part of their state. This replaces the tail-flush with a positionally-tagged buffer drained in arrival order. `flush()` walks from a monotonic index pointer, resolving text immediately and files once their `'end'` has fired, and holding later entries when the cursor lands on a still-streaming file. The backing FormData now matches the payload's order, restoring the contiguity assumption (and fixing the long-standing reorder as a side effect). The same change is applied to all five copies in `react-server-dom-{webpack,turbopack,parcel,esm,unbundled}`. Two new tests cover the multi-file interleave. fixes vercel/next.js#93822
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Fixes a regression from #36425 where referenced
FormDataentries can be dropped bydecodeReplyFromBusboywhen files are interleaved with text fields in the payload.decodeReplyFromBusboyqueues text fields that arrive while a file is being streamed and flushes them after the last file's'end', working around busboy emitting'end'deferred relative to subsequent'field'events. With multiple files interleaved with text, this loses the relative order of the affected text entries. The reorder was a long-standing but invisible issue — entries came back in the wrong order but were all present — until #36425 tightened how referenced FormData entries are collected from the backing store to rely on them being contiguous. With that assumption violated, referenced FormDatas can now come back with some entries dropped. The pattern is most easily surfaced throughuseActionStateactions that return the submittedFormDataas part of their state.This replaces the tail-flush with a linked list of pending files. Text fields that arrive while a file is in flight are queued on the tail file's
queuedFields; fields that arrive when the list is empty resolve immediately.flush()walks from the head, resolving each completed file followed by its queued fields, and stops at the first file that hasn't ended yet. The backing FormData now matches the payload's order, restoring the contiguity assumption (and fixing the long-standing reorder as a side effect). The same change is applied to all five copies inreact-server-dom-{webpack,turbopack,parcel,esm,unbundled}. Two new tests cover the multi-file interleave.fixes vercel/next.js#93822