saphid--frame-control/docs/apk-repos.md

APK repositories

Frame Control supports F-Droid-format repositories, including F-Droid, F-Droid archive, IzzyOnDroid and user-provided HTTPS repositories. Repository indexes are authenticated before their apps appear. Search lists builds with Android API ≤30 and arm64-v8a or no native libraries, using the same streaming reducer as the existing catalogue. This does not guarantee an app works in Lepton.

Formats considered

Format	Users and purpose	Support in this source
F-Droid v2	F-Droid, IzzyOnDroid, self-hosted fdroidserver repositories; consumed by F-Droid clients including Droid-ify and Neo Store	Preferred: signed entry.jar authenticates entry.json; its SHA-256 authenticates index-v2.json, which supplies APK SHA-256 hashes
F-Droid v1	Older F-Droid servers and clients	Fallback: verify index-v1.jar, then read its signed index-v1.json
Obtainium configurations / exports	Obtainium users share app URLs plus source-specific filters and update settings; exports can contain a list of app configuration objects	Not imported here: configurations describe how to find releases, not one signed repository index
SideQuest listings / custom feeds	SideQuest's own app discovery and installation service	No interoperable signed custom-repository specification was established from the public project documentation examined; SideQuest needs its own adapter
GitHub release lists	Developers publish APK assets on release pages; community lists link to projects	Not a repository standard: asset naming, build selection and publisher verification vary; handled separately from this F-Droid source
Minimal JSON list	A private list could contain package, title, APK URL and SHA-256	Deliberately not introduced: unsigned hashes downloaded alongside files do not authenticate their publisher; another bespoke signing/update protocol would duplicate F-Droid

Research references (checked 2026-09-28):

• F-Droid APIs and repository setup.
• F-Droid signing keys and IzzyOnDroid's repository page and fingerprint.
• Droid-ify and Neo Store.
• Obtainium, its configuration/deep-link format, and community app configurations.
• SideQuest's public client. The absence of a specification in these materials is not proof that no historical or private custom-feed format exists.

Add a repository in Frame Control

From the Frame Control checkout, use its source-management CLI:

python3 ui/apk_sources/fdroid.py add 'https://example.org/fdroid/repo?fingerprint=YOUR_64_HEX_CERTIFICATE_FINGERPRINT' --name 'My apps'
python3 ui/apk_sources/fdroid.py list
python3 ui/apk_sources/fdroid.py search SOURCE_ID 'music'
python3 ui/apk_sources/fdroid.py download SOURCE_ID org.example.app
python3 ui/apk_sources/fdroid.py remove SOURCE_ID

Replace SOURCE_ID with the id printed by add or list. --fingerprint can also supply the pin. fdroidrepos://example.org/fdroid/repo?fingerprint=… links are accepted and converted to HTTPS. Conflicting fingerprints are refused. A URL must identify the repository directory, not its website or an index file.

Adding fetches and validates the complete index before saving the source. Without a fingerprint, Frame Control verifies the JAR signature and remembers its signer: trust on first use (TOFU). This establishes continuity with the first server response, not independent publisher identity. Obtain the published fingerprint through a trusted channel when possible; the store's Add a source form shows the pinned one ("Trusted on first use: …") so you can compare it. Re-adding an existing URL preserves its pin; changing it requires deliberately removing and re-adding it.

The API for the search/server integration is in ui/apk_sources/fdroid.py: add_repo(url, fingerprint=None, name=None), remove_repo(source_id), set_enabled(source_id, enabled), and user_repos(). The module also exposes sources, search, details, and download from the shared source contract. This change supplies the CLI and API; the integrated source-management UI is separate work. Built-in sources can be disabled but cannot be removed.

Settings and pins live in frame_host.data_dir('apk-repos.json') (~/Library/Application Support/Frame Control/apk-repos.json on macOS). Authenticated reduced indexes and APKs live under frame_host.cache_dir('apk-sources'); indexes refresh after 24 hours. An expired index is still served (marked stale in the store) while it refreshes in the background; a failed refresh is retried after 10 minutes. Only the running Frame Control app prunes cached APKs (at start and after store downloads); the command-line tools never do. The existing catalogue's unverified index cache is never treated as authenticated.

Rollback protection: each repository's newest accepted signed index timestamp is kept in apk-repo-state.json next to the settings, and an older index is refused. Once a repository has served a v2 entry.jar, a missing entry.jar is an error rather than a reason to fall back to index-v1.jar. entry.jar must be signed with SHA-2 (SHA-1 is still accepted for legacy index-v1.jar). Removing a repository clears its state.

Publish your own repository

Only publish free APKs you own or have the developer's permission to distribute. Do not publish paid app mirrors or bypass store licences. Check distribution terms before adding someone else's repository; this module does not infer legal permission from a signature or automatically audit a repository's terms.

Install a current fdroidserver and its documented Android/Java dependencies on the publishing machine, then:

mkdir my-fdroid
cd my-fdroid
fdroid init
# Set repo_url in config.yml to https://example.org/fdroid/repo
# Also set repo_name and repo_description; keep the generated signing key safe.
cp /path/to/your-free-app.apk repo/
fdroid update --create-metadata
# Review the generated metadata (name, summary, licence, source and website).
fdroid update

Serve the generated repo directory at that HTTPS URL, including APKs, icons, entry.jar, index-v2.json and index-v1.jar. Do not publish the private signing keystore or configuration passwords. Configure fdroidserver's serverwebroot and run fdroid deploy for managed publication, or copy the public directory with your existing deployment tool. Publish the SHA-256 repository certificate fingerprint displayed by fdroidserver in a link such as https://example.org/fdroid/repo?fingerprint=….

Keep the repository signing key backed up: changing it breaks existing pins. For updates, add the new APK, edit metadata as needed, run fdroid update and publish again. Test the published URL with Frame Control's add, search and download commands. The above publisher setup is documented from fdroidserver; it was not executed as part of this implementation.

Verification and limits

The stdlib verifier supports one RSA PKCS#1 v1.5 JAR/CMS signer with a key of 2048–8192 bits; SHA-256/384/512 and legacy SHA-1 digest encodings are recognized. It checks the signer certificate pin, the signature over .SF, the whole-manifest digest, and the manifest's digest of the JSON member. ECDSA, DSA, RSA-PSS, multiple signers and section-only .SF manifests are rejected. Certificates are pinned identities, not validated as Web PKI chains. HTTPS certificates are separately checked by Python's normal TLS validation.

v1 fallback occurs only when entry.jar returns HTTP 404 or 410. Signature, fingerprint, index hash, TLS and server errors never trigger an unsigned fallback. APKs are cached by SHA-256 and checked again before reuse. Here, verified: true means the bytes match the signed repository's APK hash; it is not an independent APK publisher-signature or runtime compatibility verdict. There is no repository timestamp rollback/expiry policy or automated signing-key rotation yet. An old correctly signed index can still validate.

Offline fixtures exercise v2, v1, TOFU, pin changes, disabled sources, cache reuse, URL rejection and corruption of every signature/hash layer. On the Mac, the real IzzyOnDroid repository was added with its published pin, searched for Tiny Music Player, and its 16,520-byte APK downloaded with SHA-256 d7bcb24d101b04beb3394b695b24be4e2c3d6ed702f1d0e06bc4dd707f64d86a. No headset connection or installation was performed.