DPUB IG Telco, 2015-10-19: Service Workers, extended description analysis

See minutes online for a more detailed record of the discussions. (The headers below link into the relevant sections of the minutes.)

Overview of Service Workers

Jake Archibald, one of the editors of the Service Workers Draft, was a guest of the meeting, and gave a short overview of Service Workers.

(The reason of this discussion is because Service Workers have been identified as one of the possible means to create a PWP Architecture.)

SW itself is just a javascript runtime that can operate on a separate thread. Key difference in life cycle is that it can spin up without the existence of pages on the origin. The starting point for the web becomes the SW rather than the page. One of the key features is offline because you get a fetch event for every request the page makes, so you can create an offline experience by listening for fetch events. You get to choose what to do, the default being nothing, but you can create a response, a string or blob and send that back, you can fetch things from named caches, from IndexedDB, etc. The Gold standard of this type of app development is “offline first”, i.e., create the offline experience before even attempting to go to the network, seeing the network as progressive enhancement. The aim is to ship stuff from the caches as quickly as possible, and then go to the network. Lots of user experience we are trying to figure out now, but the SW specification doesn't make any of these decision.

Service workers can also be used to unpack content on the fly, whether the packed content is in some ZIP format or other packaging format (the issue around the streaming ability of ZIP and other formats came up during the discussion).

There were some discussion about the availability of SW in browsers (is true for Chrome and Firefox, Microsoft Edge is in the process of development, nothing is known of Safari). There are also plans to create more tutorials and introductory texts for the specification.

Subsequent discussions on the meeting concentrated on the experience using Service Workers. Dave Cramer, from Hachette, has already played with this with a good first impression. The Readium consortium has also tried using it, and Daniel Wreck, from the consortium, shared his experiences and questions. The Readium proof-of-concept implementation is able to handle an EPUB content that is exploded on the web server or is able to do some ZIP unpacking (the current implementation does not do caching, only fetch intercepts). There were issues about same-origin constraints, usage of HTTPS as opposed to HTTP.

Extended Description Analysis

The PF Working group has created a document analyzing the various proposed content description techniques for accessibility purposes (i.e., usage of longdesc, aria-describedat, <detail>, etc. That document aimed describing the various needs of the publishing industry; that was now reviewed by Deborah and Mia, primarily, with comments from others. The document is now 'back' to the PF Working Group.