How to compute the positions for a Readium Web Publication?

[mickael-menu]

We have an implementer using EPUB converted to actual RWPM in their app, wanting to use the positions service.

Currently in the Readium Mobile Toolkits, we don't have an implementation of the positions service for an ebook RWPM, only for:

• EPUB
• PDF
• CBZ
• RWPM LCPDF and Divina

Should we provide a default positions service for vanilla/HTML RWPM as well?

I would argue that we can't reasonably determine positions for a real WebPub, as the layout and reading flow is not constrained. However, if a RWPM conforms to the EPUB profile ("conformsTo":"https://readium.org/webpub-manifest/profiles/epub"), we could inject the same Positions Service implementation used by the EPUB parser.

[qnga]

Injecting a Positions service into publications which conform to the EPUB profile does make sense to me. More generally, I think we should ensure that what the RWPM parser outputs with conformsTo including EPUB is similar to what the EPUB parser outputs.

[mickael-menu]

We discussed this issue during the last dev call.

Applying the EPUB positions service to a "streamed" RWPM is not easily feasible, as we need the compressed length equivalent of each resource. Fetching all the resources to calculate the positions list is also not desirable.

The recommended approach is to have the server provides explicitly the positions list as a JSON document, as described in the specification, with a link in the RWPM.

For RWPM conforming to the EPUB profile, we can fallback in two specific cases:

• If we have a packaged RWP, then we can use the regular EPUB positions service.
• If the RWPM contains extended metadata for each reading order resources with the archive compressed entry length, then we could use the regular EPUB positions service.