Compression dictionary transport

The compression dictionary transport specification has moved to the IETF: Compression Dictionary Transport

Changelog

These are the changes that have been made to the specs as it has progressed through various standards organizations and based on developer feedback during browser experiments.

July 2024

• The dictionary link relation type was changed to compression-dictionary.
• The br-d content encoding changed to dcb and a header with the hash of the dictionary was added to the stream.
• The zstd-d content encoding changed to dcz and a header with the hash of the dictionary was added to the stream.
• The Content-Dictionary header was eliminated (since the dictionary hash was moved into the dcb and dcz response stream).

Feb 2023

• The Sec-Available-Dictionary request header changed to Available-Dictionary.
• The value of the Available-Dictionary request header changed to be a Structured Field Byte Sequence (base-64 encoding of the dictionary hash, surrounded by colons) instead of hex-encoded string.
• The content encoding string for brotli with a dictionary changed from sbr to br-d.
• The match field of the Use-As-Dictionary response header is now a URLPattern.
• The expiration of the dictionary now uses the cache expiration of the dictionary resource instead of a separate expires.
• The server can provide an id in the Use-As-Dictionary response header which is echoed in the Dictionary-ID request header by the client in future requests.
• The server needs to send a Content-Dictionary response header with the hash of the dictionary used when compressing a response with a dictionary (must match the Available-Dictionary from the request).
• match-dest was added to the Use-As-Dictionary response header to allow for matching on fetch destinations (e.g. match-dest=("document" "frame") and have the dictionary only be used for document requests).