Adds support for an explicit time-to-live for dictionaries used in Compression Dictionary Transport. This is a backward-compatible extension to the "Use-As-Dictionary" HTTP response header that adds a "ttl" parameter. The ttl is the number of seconds after the dictionary was last fetched that it is usable as a compression dictionary and overrides the default expiration (which is to expire when the underlying resource expires from the HTTP cache). For example: Use-AsDictionary: match="/*", ttl=600 Would make the response available as a compression dictionary for 10 minutes independent of the HTTP caching headers. This capability was part of the original feature but dropped during the standards process because of a lack of compelling use cases at the time. New use cases have emerged as the feature gains adoption that make it useful to add as an extension. Doc: https://docs.google.com/document/d/1uAutnUWpC6V-ka_MA-4m74YV12LAA6qP1sYjy97S2-0/edit?usp=sharing
This allows for developers to use non-cacheable HTTP responses as dictionaries for future requests (i.e. HTML documents). It also allows for explicitly shortening the lifetime of a dictionary for long-lived resources (to minimize cache variants which vary on Available-Dictionary).
Docs: https://docs.google.com/document/d/1uAutnUWpC6V-ka_MA-4m74YV12LAA6qP1sYjy97S2-0/edit?usp=sharing
Explainers: https://docs.google.com/document/d/1uAutnUWpC6V-ka_MA-4m74YV12LAA6qP1sYjy97S2-0/edit?usp=sharing