OPDS to provide multiple links per book

[rgaudin]

Due to openzim/cms#300 and the reliance of both ZIM and Metalink links by readers, we'd like to be able to get both an application/x-zim and an application/metalink4+xml link for our books

[rgaudin]

FYI here's the current readers usage of this information.

reader	Using URL from	.meta4 suffix handling	Multiple links safe?
libkiwix	Sets downloadUrl from link with rel="http://opds-spec.org/acquisition/open-access"	-	❌ will use last open-access
PWA	Uses Link with both rel="http://opds-spec.org/acquisition/open-access" type="application/x-zim"	Treat .meta4 as Metalink	✅ will use first matching
Apple	downloadUrl from libkiwix	removes suffix if it exists	❌ libkiwix
Android	downloadUrl from libkiwix	removes suffix if it exists	❌ libkiwix
Desktop	downloadUrl from libkiwix	passes it directly to aria2 or libtorrent	⚠️ may not benefit from metalink/torrent
Cardshop	Uses Link with type="application/x-zim"	removes suffix if it exists	✅ will use last x-zim
Seeder	Uses Link with type="application/x-zim"	removes suffix if it exists	✅ will use last x-zim

libkiwix will need to decide how to expose the other links and what goes into the downloadUrl (or rename this prop). Kiwix-desktop will have to adapt as it can download differently.

---

 <entry>
    <id>urn:uuid:00072115-bf0f-1e6e-e1cd-9d8c0751f7ed</id>
    <title>Klexikon – das Kinderlexikon</title>
    <updated>2026-05-09T00:00:00Z</updated>
    <summary>Klexikon ist die Wikipedia für Kinder.</summary>
    <language>deu</language>
    <name>klexikon_de_all</name>
    <flavour>nopic</flavour>
    <category></category>
    <tags>zum;_pictures:no;_videos:no;_details:yes;_ftindex:yes</tags>
    <articleCount>5659</articleCount>
    <mediaCount>73</mediaCount>
    <link rel="http://opds-spec.org/image/thumbnail"
          href="/catalog/v2/illustration/00072115-bf0f-1e6e-e1cd-9d8c0751f7ed/?size=48"
          type="image/png;width=48;height=48;scale=1"/>
    <link type="text/html" href="https://browse.library.kiwix.org/content/klexikon_de_all_nopic_2026-05" />
    <author>
      <name>Klexikon</name>
    </author>
    <publisher>
      <name>openZIM</name>
    </publisher>
    <dc:issued>2026-05-09T00:00:00Z</dc:issued>
    <link rel="http://opds-spec.org/acquisition/open-access" type="application/x-zim" href="https://lbo.download.kiwix.org/zim/other/klexikon_de_all_nopic_2026-05.zim.meta4" length="9807872" />
  </entry>

[kelson42]

We definitely needs this soon, but kind of blocked by kiwix/overview#59 and #1309