v130 · network / connectivity

Compression dictionary transport with Shared Brotli and Shared Zstandard

This feature adds support for using designated previous responses, as an external dictionary for content encoding compressing responses with Brotli or Zstandard.

concepts

  1. Shared CDT simulator

    Edit a dictionary and a new resource. A local server route measures regular Brotli, a real dictionary-compressed payload, the RFC dcb framing overhead, and the fallback path when the dictionary hash does not match.

  2. Library version evolution

    The chromestatus motivation calls out "incremental library updates" as the primary win. Steps through four real versions of a JS cart bundle (patch, minor, major) and contrasts the dcb delta against fresh brotli at each step.

  3. Use-As-Dictionary header builder

    Build the response header that promotes a resource into Chrome's dictionary cache. Toggle match-dest chips, edit the URL pattern, and probe future requests live to see which would actually pick up the dictionary.

  4. Handshake protocol walkthrough

    Five-step browser↔server ladder diagram for the full CDT handshake: initial fetch, dictionary registration, follow-up request carrying Available-Dictionary: :sha256:, the dcb-encoded delta response, and the plain Brotli fallback when no valid dictionary can be used.

why it shipped

If the browser and server share a dictionary, using the dictionary for compression can significantly reduce the amount of data transferred. This is especially useful for incremental library updates, or when browsing multiple pages that have a lot of common parts in their files.

references