high_level_overview.md

High level overview

• Uses lnd as a daemon/library because it fully conforms to the BOLT specifications and is easy to cross-compile and run on mobile platforms.
• rawtx is cross compiled using xgo. xgo brings up a docker image with all the build tools required for compiling Go into different platforms. It also supports building an .aar package for Android and a .framework package for iOS.
• The UI/app is built using react-native, which gives us the performance of a native app with development convenience of Javascript.
• Architecture looks like: react-native -> (glue) -> lnd
  • glue here is the native code (Java on Android and objC on iOS) that allows react-native to manage and call lnd. glue let's us:
    • start, stop and query the state of lnd,
    • write, read files, scan QR codes,
    • make REST calls to lnd,
    • on Android, manages the background lnd process.
• To support multiple wallets, the app has a wallet.conf that keeps track of all wallets. multi-wallet support from the very beginning sets user expectations and allows things like:
  • running Bitcoin and Litecoin(when ready) wallets side-by-side,
  • running multiple Bitcoin wallets (testnet or mainnet when ready),
  • allows adding remote wallets(coming soon) for those running their own nodes,
    • also will enable monitoring of multiple remote nodes when prometheus is merged into lnd,
  • allows shipping 2 binary versions of lnd (ex: lnd upgrades from 0.4.2 to 0.5),
    • it's possible that there will be backwards-incompatible changes, by having 2 binaries we can use the new binary for new wallets and old binary for existing wallets, prompting the user to switch funds,
    • makes it possible to ship a new lnd version and detect regression on newly created wallets, etc.
  • allows having additional implementations like c-lightning for some wallets.
• On Android, the lnd daemon is isolated in it's own process, so it's easier to manage and when it hangs or shutdowns, the whole process is removed, keeping the app's own process "clean" and makes it more difficult for native code to crash the app.
• On iOS, lnd runs in the same process as the main app and there are far more restrictions on memory/cpu/processes, so when the wallet is closed, the user can't reopen another wallet without quitting the app.