76 lines
3.2 KiB
Markdown
76 lines
3.2 KiB
Markdown
# Flamenet Messenger. Android
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The Android app, and the two libraries under it. The product's site is at
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<https://flamenetmessenger.com>.
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```
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engine/ the protocol: X3DH, Double Ratchet, sealed sender, safety numbers,
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key transparency. Plain Kotlin/JVM, no Android in it at all.
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client/ the relay transport: HTTP, auth, the §8 routes.
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app/ the Compose app.
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interop/ the cross-engine driver; not shipped.
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```
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`engine` and `client` are deliberately plain JVM libraries. The protocol has
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nothing to do with Android, and keeping it off the platform means their tests
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run anywhere a JVM does, no SDK, no emulator, no device, which is also what
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lets them gate in CI on Linux:
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```
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./gradlew :engine:test :client:test
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```
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The app's own unit tests need the Android SDK but still no emulator
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(Robolectric):
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```
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./gradlew :app:testDebugUnitTest
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```
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## Where it stands
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**[PARITY.md](PARITY.md) is the definition of done for this app, read that,
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not this.** Every row there names the iOS file it came from so it can be
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re-checked rather than trusted. Headlines: messaging, groups, attachments,
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voice notes, stories, calls, sealed sender, key transparency and the encrypted
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vault are built and tested, and a cross-platform round trip against iOS is
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verified.
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If a claim here ever disagrees with PARITY.md or with the tree, believe those,
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and fix this.
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## Why the engine came first, and is held to the vectors
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An Android client needs the protocol implemented a third time, and the third
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implementation is the one that finds the places where the specification says
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less than the two existing engines quietly agreed on, but only if it is
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written against the spec and the published vectors rather than against a
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reading of our own Swift and JavaScript. So the engine is held to
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`test/vectors/protocol-v1.json` in
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[flamenet-e2e](https://gitlab.com/paulhitt/flamenet-e2e), the same file the
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other two engines are checked against, read from that repository rather than
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copied here, because a copied vector file drifts and a drifting vector file
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stops being a check. `PublishedVectorsTest` looks for it beside this checkout
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and fails loudly if it cannot find it; `FLAMENET_VECTORS` overrides the search.
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Two implementations that agree may both be wrong in the same way, especially
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when one was written while reading the other. The audit-path ordering in §19 is
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the worked example: a top-down reading of a bottom-up path produces the correct
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root for every left-spine index, so it passes any test that only checks index
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0. The vector file pins a right-descending index for that reason, and the
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Kotlin tests assert both that the published path verifies and that the same
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path reversed does not.
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If this engine ever disagrees with the file, the interesting question is which
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of the three is wrong, not this one by default.
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## Contributing and security
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- [CONTRIBUTING.md](CONTRIBUTING.md), building (JDK 21, `JAVA_HOME` is not
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optional on a Mac), the test gate, and the platform traps that cost an hour
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each.
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- [PARITY.md](PARITY.md), what iOS does, what this does, and what is left. It
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is the definition of done for this app.
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- [SECURITY.md](SECURITY.md), threat model and where to send a vulnerability
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report. **Not an issue tracker matter:** security@flamenetmessenger.com.
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