feat(effect): add HttpMiddleware.compression for gzip/deflate response compression

[kitlangton]

Summary

Adds an HTTP response compression middleware so Effect HttpApi users don't have to roll their own. Effect-smol's HttpMiddleware ships logging, tracing, and CORS, but no compression — Hono, Express, Fastify, and nginx all ship one.

This is platform-agnostic: it uses the Web Standard CompressionStream (available in Node 18+, Bun, Deno, and browser-style runtimes) instead of node:zlib, so it works anywhere effect-smol runs.

What's added

• HttpMiddleware.compression(options?) — middleware that conditionally compresses response bodies with gzip or deflate.
• HttpRouter.compression(options?) — matching Layer<never, never, HttpRouter> registration, mirroring the cors pattern.
• HttpServerResponse.removeHeader — small public addition; the compression middleware uses it to clear stale Content-Length after swapping in a Stream body of unknown length.

Defaults (mirroring Hono's compress)

• threshold: 1024 bytes
• compressibleContentType: regex covering text/*, common application/* (json/xml/javascript/wasm/…), image/svg+xml, +json/+xml/+yaml/+text suffixes, etc. text/event-stream is always excluded so SSE chunks flow immediately.
• encodings: ["gzip", "deflate"] — gzip preferred when both are accepted. br is intentionally not included; it would need separate handling and isn't supported by CompressionStream everywhere.
• skip?: (request) => boolean — user predicate (e.g., to bypass specific paths).

Skip conditions

• HEAD requests
• Response already has Content-Encoding
• Response has Cache-Control: no-transform
• Content type not in the allowlist, or is text/event-stream
• Known Content-Length < threshold
• Body is Empty / Raw / FormData (only Uint8Array and Stream are compressed)

When compressing

• Replaces body via Stream (or Uint8Array if the original body was Uint8Array)
• Sets Content-Encoding
• Drops stale Content-Length for stream bodies (compressed length unknown)
• Merges Accept-Encoding into any existing Vary header (preserving e.g. Vary: Origin from CORS)
• Weakens strong ETag to W/...

Test plan

15 new unit tests covering all branches:

• Compresses Uint8Array body with gzip; round-trip decompresses correctly
• Prefers gzip when both gzip and deflate are accepted
• Compresses Stream body and clears stale Content-Length
• Skips when Accept-Encoding is missing
• Skips when no encoding is supported (e.g., br only)
• Skips bodies smaller than threshold
• Skips non-compressible content types (e.g., image/png)
• Skips text/event-stream
• Skips when response already has Content-Encoding
• Skips when Cache-Control: no-transform
• Skips HEAD requests
• Respects user skip predicate
• Merges Accept-Encoding into existing Vary header
• Weakens strong ETag ("abc" → W/"abc")
• Leaves weak ETag unchanged
• pnpm check:tsgo, pnpm lint-fix, pnpm docgen
• All 107 test/unstable/http/ tests pass
• Changeset added (minor)

Open questions for the maintainers

• Naming: I went with HttpMiddleware.compression to match the existing module style; happy to rename to compress if that's preferred.
• Brotli: skipped intentionally for a first cut; CompressionStream doesn't accept "br" in Node, so it would need a Node-only path. Easy follow-up.
• Configuration shape: the compressibleContentType option is a single RegExp (matching Hono). Open to making it a predicate (contentType) => boolean if more flexibility is wanted.

[changeset-bot]

🦋 Changeset detected

Latest commit: ce75a9c

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 27 packages

Name	Type
effect	Major
@effect/opentelemetry	Major
@effect/platform-browser	Major
@effect/platform-bun	Major
@effect/platform-node-shared	Major
@effect/platform-node	Major
@effect/vitest	Major
@effect/ai-anthropic	Major
@effect/ai-openai-compat	Major
@effect/ai-openai	Major
@effect/ai-openrouter	Major
@effect/atom-react	Major
@effect/atom-solid	Major
@effect/atom-vue	Major
@effect/sql-clickhouse	Major
@effect/sql-d1	Major
@effect/sql-libsql	Major
@effect/sql-mssql	Major
@effect/sql-mysql2	Major
@effect/sql-pg	Major
@effect/sql-pglite	Major
@effect/sql-sqlite-bun	Major
@effect/sql-sqlite-do	Major
@effect/sql-sqlite-node	Major
@effect/sql-sqlite-react-native	Major
@effect/sql-sqlite-wasm	Major
@effect/openapi-generator	Major

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