[darkweak]

Summary

• esi.NewStream(dst, req): an io.WriteCloser that processes ESI tags while the document is written. Static content goes out immediately, includes are fetched concurrently and written in document order, and the destination is flushed whenever output waits on an include or more input. Tags split across writes are handled; Write never blocks on an include.
• esi.Parse: same signature, now fetches includes in parallel and builds the output in one pre-sized allocation instead of re-appending the whole buffer after each tag.
• writer.Writer: thin http.ResponseWriter over the stream. Middlewares become NewWriter → next.ServeHTTP → Close, removing the busy-wait goroutine (and its data race) from caddy, roadrunner and traefik.
• Efficiency: byte search instead of regexes for tag/closing detection (offline parse ~2× faster, ~90× less memory); includes share a pooled transport (64 idle conns/host), use the request context, and no longer leak the response body on alt fallback.
• Go 1.27 across all modules and CI; caddy upgraded v2.6.4 → v2.11.9 (old quic-go doesn't build on Go ≥ 1.21); golangci-lint config migrated to v2; traefik vendor refreshed.

Breaking changes / behaviour differences

• writer.NewWriter(rw, rq) no longer takes a *bytes.Buffer; AsyncBuf, Done, Iteration removed; Close() must be called.
• Upstream status codes are passed through (previously always 200).
• Content-Length is dropped properly; the invalid Content-Encoding: chunked header is no longer set.
• Unsupported tags (e.g. <esi:try>) are emitted verbatim instead of crashing Parse.
• A failing include without onerror="continue" is removed instead of truncating the rest of the document.
• Parse no longer mutates its input.

Test plan

• go test -race ./... in the root module (tests now start their own fixture server on :9080, or reuse the CI caddy)
• New tests: every chunk split / byte-by-byte streaming vs Parse, parallel includes (20 × 200 ms in ~210 ms), flush before slow include, write errors, writer status/Content-Length handling
• caddy middleware integration test and roadrunner tests under -race
• golangci-lint run (v2.13): 0 issues on the root module
• Traefik plugin loads under Yaegi (traefik:latest, middleware/traefik stack) and processes vars, remove, include and alt fallback. Yaegi does not support generic stdlib types nor the clear/min builtins, so the core package avoids them.

[p0358]

Dang it, I did local ESI reimplemention 2 weeks ago and forgot to PR it xD

Should I still push it somewhere for comparison in case there's anything useful there to salvage?

[darkweak]

I think you can push a PR 😄