feat: use SSE in query.live to avoid weird middleman quirks with normal streamed responses - #15957
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Rich-Harris
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Rich-Harris
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June 5, 2026 19:17
This was referenced Jun 5, 2026
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This PR was opened by the [Changesets release](https://github.com/changesets/action) GitHub action. When you're ready to do a release, you can merge this and the packages will be published to npm automatically. If you're not ready to do a release yet, that's fine, whenever you add more changesets to main, this PR will be updated. # Releases ## @sveltejs/kit@2.63.1 ### Patch Changes - fix: use SSE for `query.live` ([#15957](#15957)) - fix: use forward slashes in the generated `env.d.ts` import path on Windows ([#15977](#15977)) - fix: allow `$app/environment` with a warning when `explicitEnvironmentVariables` is enabled ([#15980](#15980)) - fix: avoid importing Vite while validating explicit environment variables ([#15953](#15953)) - docs: adjust the release version of explicit env vars ([#15968](#15968)) - fix: ensure `version` is defined when importing from `$app/env` with explicit environment variables ([#15971](#15971)) Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
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Don't think this helps with nginx. Just checked the codebase, it has this in the endpoint: return new Response(stream, {
headers: {
'Content-Type': 'text/event-stream',
'Cache-Control': 'no-cache',
'Connection': 'keep-alive',
'X-Accel-Buffering': 'no', // Disable buffering for nginx
},
}); |
Rich-Harris
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This PR was opened by the [Changesets release](https://github.com/changesets/action) GitHub action. When you're ready to do a release, you can merge this and the packages will be published to npm automatically. If you're not ready to do a release yet, that's fine, whenever you add more changesets to version-3, this PR will be updated.⚠️ ⚠️ ⚠️ ⚠️ ⚠️ ⚠️ `version-3` is currently in **pre mode** so this branch has prereleases rather than normal releases. If you want to exit prereleases, run `changeset pre exit` on `version-3`.⚠️ ⚠️ ⚠️ ⚠️ ⚠️ ⚠️ # Releases ## @sveltejs/kit@3.0.0-next.2 ### Patch Changes - fix: use SSE for `query.live` ([#15957](#15957)) - fix: use forward slashes in the generated `env.d.ts` import path on Windows ([#15977](#15977)) - fix: avoid importing Vite while validating explicit environment variables ([#15953](#15953)) - docs: adjust the release version of explicit env vars ([#15968](#15968)) - fix: ensure `version` is defined when importing from `$app/env` with explicit environment variables ([#15971](#15971)) Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
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`read_stream` accumulates decoded text in one string, re-runs `indexOf` over the whole buffer after every transport chunk and re-slices the buffer for every emitted record. When one frame spans many chunks, every prefix is rescanned and total work grows quadratically with frame size. This parser sits behind streamed page data and remote functions (NDJSON) and `query.live` (SSE), so the cost lands on the client for large payloads. With this change only newly decoded text is searched. Already searched text accumulates in an array and is joined once per completed frame. The last `delimiter.length - 1` characters stay in the unsearched tail so a delimiter split across chunk boundaries still matches. One 2 MiB frame, Node 22 x64, median of repeated runs: | transport chunks | before | after | speedup | | ---: | ---: | ---: | ---: | | 2048 × 1 KiB | 1720.7 ms | 4.0 ms | 429× | | 512 × 4 KiB | 431.0 ms | 3.2 ms | 135× | | 128 × 16 KiB | 111.5 ms | 3.1 ms | 36× | | 32 × 64 KiB | 31.3 ms | 3.1 ms | 10× | Many small records, the common path, get slightly faster (2 MiB of 64 byte records in 16 KiB chunks, ~21 ms to ~15 ms) because the old code re-sliced the buffer once per record. Output is unchanged. The rewrite matched the previous implementation across 4000 randomized cases covering both delimiters, delimiters split between chunks, multibyte UTF-8 split between chunks and trailing unterminated records. The new unit tests also pass against the previous implementation. `read_stream` was extracted in #15957 and last changed in #16423. No open PR modifies `stream.js`, `ndjson.js` or `sse.js`. --- ### Before submitting the PR, please make sure you do the following - [ ] It's really useful if your PR references an issue where it is discussed ahead of time. In many cases, features are absent for a reason. For large changes, please create an RFC: https://github.com/sveltejs/rfcs - [x] This message body should clearly illustrate what problems it solves. - [x] Ideally, include a test that fails without this PR but passes with it. ### Tests - [x] Run the tests with `pnpm test` and lint the project with `pnpm lint` and `pnpm check` ### Changesets - [x] If your PR makes a change that should be noted in one or more packages' changelogs, generate a changeset by running `pnpm changeset` and following the prompts. Changesets that add features should be `minor` and those that fix bugs should be `patch`. Please prefix changeset messages with `feat:`, `fix:`, or `chore:`.
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closes #15956
closes #15921
closes (maybe) #15790?
Some middlemen (antivirus, nginx) do weird buffer-y things with streamed responses, in spite of the no-store cache directives we use. SSE is more universal and seems to bypass some of these behaviors. TBD on whether this works for the nginx issue.
Due to weird GitHub quirks I couldn't push to @IAkumaI's branch. This still contains his commits.