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dictionary-worker

dictionary-worker is Patrick Meenan's open-source reference implementation of RFC 9842: Compression Dictionary Transport, running the full dictionary lifecycle inside a single Cloudflare Worker using WASM-compiled Zstandard. Meenan is the author of RFC 9842; the Worker is an existence proof that origin-side RFC 9842 implementation is possible today, without waiting for Cloudflare's managed rollout.

What it does

• Serves Use-As-Dictionary response headers on configured resource paths.
• Accepts Available-Dictionary request headers on subsequent requests and delta-compresses the response against the cached dictionary using WASM-Zstandard.
• Emits Content-Encoding: dcz (delta-compressed Zstandard) response bodies.
• Falls back to standard compression when the client doesn't advertise dcb/dcz support or doesn't have a dictionary.
• Manages dictionary bytes + cache-variant keys inside the Worker runtime.

Why it matters as a systems-design exemplar

The Worker shows two things:

1. RFC 9842 is implementable today without CDN-tier managed support — any origin running a Cloudflare Worker (or any compute layer with WASM-Zstandard + cache access) can ship shared-dictionary compression now.
2. But the origin-side cost is high enough to motivate moving it to the CDN. Cloudflare's shared-dictionaries launch post names the complexity explicitly — generate, serve, match, compress, fall back, manage cache variants, handle mid-deploy client-population splits — and argues "this is a coordination problem that belongs at the edge." The existence of dictionary-worker doesn't invalidate the claim; it's precisely the thing most customers won't build for themselves.

dictionary-worker is therefore the canonical what Phase 2 of systems/cloudflare-shared-dictionaries absorbs: advanced customers today run something like this; Phase 2 managed dictionaries turn it into a CDN-native feature that the long tail of zones can use without touching the implementation.

See also

• systems/rfc-9842-compression-dictionary-transport — the standard Meenan authored.
• systems/cloudflare-shared-dictionaries — the managed CDN feature that supersedes the need for origin-side implementations.
• systems/cloudflare-workers — the compute substrate.
• patterns/edge-managed-protocol-complexity — broader framing of why protocol-implementation complexity migrates to CDNs.

Seen in

• sources/2026-04-17-cloudflare-shared-dictionaries-compression-that-keeps-up-with-the-agent — named as the canonical existing customer implementation before Cloudflare's managed rollout: "some people have already built their own implementations like RFC author Patrick Meenan's dictionary-worker, which runs the full dictionary lifecycle inside a Cloudflare Worker using WASM-compiled Zstandard (as an example)."