flipcash-shared-core-spm

Swift Package distribution for SharedCore — the Kotlin that the Flipcash iOS and Android apps both run, built as an XCFramework and wrapped in a Swift API.

What's shared

Not everything that could be shared is here. This is the code where a difference between the two apps isn't cosmetic: a different derived key is a different account, a different signature is a rejected transaction, and a different curve answer is a mispriced trade. UI, networking, and storage stay native on both platforms.

Scannable codes

The geometry behind the tip card and the scanner. KikCodeSpec holds the drawing spec — ring count, bits per ring, the badge well ratio — which used to live twice, with ratios that agreed and a frame that didn't. KikCode.figure(payload:dimension:) turns a payload into the mark and badge CGPaths the code view draws, and KikCode.svg(payload:) renders the same code for export.

LuminancePlane is the decode side: how many bytes the native scanner reads out of a camera frame's luminance plane, and how to unpad one whose rows are stride-aligned. Both apps had this wrong in opposite directions before it moved here.

Account keys and recovery

BIP39 phrase to seed, and SLIP-10 hardened derivation on top of it — SharedDerivation.seed(mnemonic:passphrase:) and SharedDerivation.derivedKey(seed:hardenedIndexes:). An account's keys come from here, so the same recovery phrase has to produce the same address on either platform.

Signing and hashing

SharedEd25519 for keypairs, signing, verification, and on-curve checks. SharedHash for SHA-256, SHA-512, HMAC, and PBKDF2-SHA512. Base58 for account addresses. These are the primitives Solana addresses and transaction signatures are built from; both platforms compile the same vendored C reference implementation underneath ed25519.

Pricing

SharedBondingCurve — spot price at a given supply, tokens to value and back, and the rate for an exchange, read against the discrete pricing and cumulative tables. This was two implementations with different precision handling, UInt128 on the Swift side and BigDecimal on the Kotlin one.

This repository is generated

The source lives in code-payments/code-android-app under kmp/shared-core. Everything here except this README — Package.swift, Sources, Tests, and the SharedCore.xcframework.zip release assets Package.swift points at — is produced by that repo's Publish SharedCore workflow.

Do not edit Package.swift by hand; the next publish overwrites it.

Using it

.package(url: "https://github.com/code-payments/flipcash-shared-core-spm", from: "0.6.0")

import SharedCoreKit

SharedCoreKit is the only product. It's a thin Swift target over the SharedCore binary framework, so callers get Swift types and default arguments rather than the Kotlin framework's own surface of KotlinByteArray and .shared singletons.

Cutting a release

Run the Publish SharedCore workflow in code-payments/code-android-app, passing the version to publish. It builds the XCFramework, uploads it as a release here, rewrites Package.swift to point at that asset, tags the commit with the version, and writes the release notes from the commits since the last publish. The Kotlin it was built from is tagged shared-core/<version> in code-android-app.