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cw-out: avoid O(n^2) work while buffering paused output - #22896
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MegaManSec wants to merge 3 commits into
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MegaManSec wants to merge 3 commits into
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When a header callback returns CURL_WRITEFUNC_PAUSE, cw_out_do_write downgraded the resulting CURLE_AGAIN to CURLE_OK, so the HTTP/2 layer kept feeding it every remaining decoded header field in the current HPACK block instead of stopping. on_header() now returns NGHTTP2_ERR_PAUSE while paused, nghttp2's documented mechanism to halt decoding mid-block, and the pending-input loop breaks on pause too. Separately, the pause buffer's cw_out_buf chain was a stack replayed via recursive tail-hunting, and its buffered length was recomputed by a full list walk on every append: both O(n^2) over the chain. Track a tail pointer and a running length instead.
Contributor
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As I understand it, |
Contributor
Author
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Right, let's get rid of that and just keep this pr focused on one thing (the perf bump attempt). Will chahge |
MegaManSec
changed the title
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Author
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Updated as discussed: removed the HTTP/2 pause behavior changes. This PR now focuses only on the cw-out paused-buffer performance improvement. |
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🟢 Approval recommended
The queue invariants, byte accounting, cleanup, and output ordering remain correct.
Pull request overview
Optimizes paused-output buffering while preserving FIFO callback behavior.
Changes:
- Adds constant-time tail insertion and buffered-length tracking.
- Replaces recursive reverse-list flushing with iterative oldest-first flushing.
File summaries
| File | Description |
|---|---|
lib/cw-out.c |
Optimizes buffer append, size accounting, cleanup, and flushing. |
Review details
- Files reviewed: 1/1 changed files
- Comments generated: 0
- Review effort level: Balanced
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Thanks! |
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Improves paused-output buffer performance without changing protocol behavior.
The buffer chain now keeps a tail pointer, so appending does not repeatedly walk the list, and tracks the total buffered length instead of rescanning every buffer on each append. Flushing proceeds from the oldest buffer iteratively.
This reduces buffering many paused writes from quadratic list/replay bookkeeping to linear work.