Add UniFFI Kotlin bindings for payjoin-ffi

.github/workflows/kotlin.yml

@@ -0,0 +1,42 @@
+name: Build and Test Kotlin
+on:
+  workflow_run:
+    workflows: ["Flake maintenance"]
+    types: [requested]
+    branches:
+      - "update_flake_lock_action"
+  pull_request:
+    paths:
+      - payjoin-ffi/**
+      # The jobs run inside the flake's kotlin dev shell, so changes to
+      # the flake change this workflow's environment.
+      - flake.nix
+      - flake.lock
+      - .github/workflows/kotlin.yml
+
+jobs:
+  build-kotlin-and-test:
+    name: "Build and test kotlin"
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os: [ubuntu-26.04, macos-latest]
+    env:
+      RUSTUP_TOOLCHAIN: 1.85.0
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v6
+      - name: "Install Rust 1.85.0"
+        uses: dtolnay/rust-toolchain@1.85.0
+      - name: "Use cache"
+        uses: Swatinem/rust-cache@v2
+        with:
+          shared-key: msrv-workspace
+      - name: Set up nix
+        uses: ./.github/actions/setup-nix
+      - name: "Build and test"
+        run: nix develop .#kotlin -c bash ./payjoin-ffi/kotlin/contrib/test.sh
+      - name: "Compile production bindings"
+        run: |
+          nix develop .#kotlin -c env PAYJOIN_FFI_FEATURES= bash ./payjoin-ffi/kotlin/scripts/generate_bindings.sh
+          nix develop .#kotlin -c bash -c 'cd payjoin-ffi/kotlin && ./gradlew --no-daemon compileKotlin'

flake.nix

@@ -389,6 +389,25 @@
           BITCOIND_SKIP_DOWNLOAD = 1;
         };
 
+        kotlinDevShell = pkgs.mkShell {
+          name = "kotlin-dev";
+          packages =
+            with pkgs;
+            [
+              rustVersions.msrv
+              jdk21
+              python3
+              bzip2
+            ]
+            ++ lib.optionals pkgs.stdenv.isLinux [
+              pkg-config
+              openssl
+              clang
+            ];
+          BITCOIND_EXE = pkgs.lib.getExe' pkgs.bitcoind "bitcoind";
+          BITCOIND_SKIP_DOWNLOAD = 1;
+        };
+
         # Rust toolchain for the python dev shell: msrv pinned to match
         # payjoin-ffi/python build requirements, with per-arch targets added
         # so cargo can build artifacts under nix for payjoin-ffi/python/scripts/generate_bindings.sh
@@ -502,6 +521,7 @@
           javascript = javascriptDevShell;
           csharp = csharpDevShell;
           dart = dartDevShell;
+          kotlin = kotlinDevShell;
         };
         formatter = treefmtEval.config.build.wrapper;
         checks =

payjoin-ffi/README.md

@@ -16,6 +16,7 @@ The directories below include instructions for using, building, and publishing t
 | Dart       | linux, macOS          | [payjoin-ffi/dart](dart)             | [pub.dev](https://pub.dev/packages/payjoin)     |
 | JavaScript | linux, macOS          | [payjoin-ffi/javascript](javascript) | [npm](https://www.npmjs.com/package/payjoin)    |
 | C#         | linux, macOS, windows | [payjoin-ffi/csharp](csharp)         | [nuget](https://www.nuget.org/packages/Payjoin) |
+| Kotlin     | linux, macOS          | [payjoin-ffi/kotlin](kotlin)         | (not published)                                 |
 
 ## Minimum Supported Rust Version (MSRV)
 

payjoin-ffi/contrib/test.sh

@@ -2,7 +2,7 @@
 set -e
 cd "$(dirname "$0")/.."
 cargo test --package payjoin-ffi --verbose --features=_manual-tls,_test-utils
-BINDINGS="dart javascript python csharp"
+BINDINGS="dart javascript python csharp kotlin"
 pids=()
 tmpfiles=()
 for binding in $BINDINGS; do

payjoin-ffi/kotlin/.gitignore

@@ -0,0 +1,15 @@
+# Generated UniFFI Kotlin
+src/main/kotlin/org/
+
+# Native library copied by generate_bindings.sh
+/lib/*.so
+/lib/*.dylib
+/lib/*.dll
+
+# Gradle
+.gradle/
+build/
+local.properties
+
+.idea/
+.DS_Store

payjoin-ffi/kotlin/CONTRIBUTING.md

@@ -0,0 +1,29 @@
+# Contributing to the Payjoin Kotlin Bindings
+
+Kotlin/JVM bindings for the [Payjoin Dev Kit](https://payjoindevkit.org/), generated from
+`payjoin-ffi` with Mozilla UniFFI. This document covers building from source and running tests.
+
+## Development
+
+```shell
+git clone https://github.com/payjoin/rust-payjoin.git
+cd rust-payjoin/payjoin-ffi/kotlin
+bash ./scripts/generate_bindings.sh
+./gradlew test
+```
+
+Generation uses the in-tree `uniffi-bindgen` binary (`--language kotlin`). There is no extra Cargo
+feature on `payjoin-ffi`. By default, development generation enables `_test-utils`. For production
+bindings, set `PAYJOIN_FFI_FEATURES` to empty:
+
+```shell
+PAYJOIN_FFI_FEATURES= bash ./scripts/generate_bindings.sh
+```
+
+Protocol `close` is renamed to `closeSession` only in `[bindings.kotlin.rename]` in
+`payjoin-ffi/uniffi.toml`, so it does not clash with `AutoCloseable.close()`.
+
+With nix, `nix develop .#kotlin` provides the pinned MSRV Rust toolchain, JDK 21, and
+`BITCOIND_EXE` (via `nixpkgs`, with `BITCOIND_SKIP_DOWNLOAD=1`), and is what CI uses. Without
+nix, use a local JDK 21+ and the Gradle wrapper; `corepc-node` will download `bitcoind` on
+first test run.

payjoin-ffi/kotlin/README.md

@@ -0,0 +1,34 @@
+# Payjoin Kotlin Bindings
+
+Kotlin/JVM bindings for the [Payjoin Dev Kit](https://payjoindevkit.org/), generated from `payjoin-ffi` with UniFFI (`--language kotlin`).
+
+Payjoin lets the receiver contribute inputs to the sender's transaction. These bindings implement [BIP 78](https://github.com/bitcoin/bips/blob/master/bip-0078.mediawiki) and [BIP 77](https://github.com/bitcoin/bips/blob/master/bip-0077.md).
+
+Requires **JDK 21+**. Native `payjoin_ffi` is loaded via JNA.
+
+Protocol session teardown on pending-fallback and JSON persisters is `closeSession()`. `AutoCloseable.close()` drops the Rust handle (try-with-resources / `.use`). Other language bindings keep `close`.
+
+## Build and test
+
+```shell
+cd payjoin-ffi/kotlin
+bash ./scripts/generate_bindings.sh
+./gradlew test
+```
+
+Or `bash ./contrib/test.sh` from this directory (uses `Cargo-recent.lock`).
+
+`./gradlew test` includes a v2↔v2 integration test that starts a local payjoin directory, OHTTP relay, and bitcoind. Inside the nix `.#kotlin` shell, `BITCOIND_EXE` points at the nixpkgs
+`bitcoind` and `BITCOIND_SKIP_DOWNLOAD=1` is set, so no download happens. Outside the nix shell,
+Bitcoin Core is downloaded by corepc-node (`29_0`) on first run instead.
+
+Without nix: Rust (see repo `rust-toolchain.toml` / MSRV 1.85), JDK 21+, and the Gradle wrapper in this directory. Network access is required the first time bitcoind is fetched.
+
+## Stability
+
+Pre-1.0. Generated sources are not committed; run generate before test or pack.
+
+## Documentation
+
+- [Payjoin Dev Kit](https://payjoindevkit.org/)
+- [rust-payjoin](https://github.com/payjoin/rust-payjoin)

payjoin-ffi/kotlin/build.gradle.kts

@@ -0,0 +1,47 @@
+plugins {
+    // KGP's Gradle compatibility matrix must cover the wrapper version pinned in
+    // gradle/wrapper/gradle-wrapper.properties (currently 9.1.0). 2.1.20 only tests
+    // against Gradle up to 8.12.1; 2.3.20+ is the first stable KGP line whose matrix
+    // extends to 9.1.0 (tested up to 9.3.0).
+    kotlin("jvm") version "2.3.21"
+}
+
+repositories {
+    mavenCentral()
+}
+
+dependencies {
+    api("net.java.dev.jna:jna:5.17.0")
+    api("org.jetbrains.kotlinx:kotlinx-coroutines-core:1.10.2")
+    testImplementation(kotlin("test"))
+    testImplementation("org.jetbrains.kotlinx:kotlinx-coroutines-test:1.10.2")
+    testImplementation("org.jetbrains.kotlinx:kotlinx-serialization-json:1.8.1")
+}
+
+java {
+    sourceCompatibility = JavaVersion.VERSION_21
+    targetCompatibility = JavaVersion.VERSION_21
+}
+
+kotlin {
+    compilerOptions {
+        jvmTarget.set(org.jetbrains.kotlin.gradle.dsl.JvmTarget.JVM_21)
+    }
+}
+
+tasks.test {
+    useJUnitPlatform()
+    val libDir = layout.projectDirectory.dir("lib").asFile
+    val os = System.getProperty("os.name").lowercase()
+    val nativeName = when {
+        os.contains("mac") || os.contains("darwin") -> "libpayjoin_ffi.dylib"
+        os.contains("win") -> "payjoin_ffi.dll"
+        else -> "libpayjoin_ffi.so"
+    }
+    val native = libDir.resolve(nativeName).takeIf { it.exists() }
+    if (native != null) {
+        inputs.file(native)
+        systemProperty("uniffi.component.payjoin.libraryOverride", native.absolutePath)
+    }
+    systemProperty("jna.library.path", libDir.absolutePath)
+}

payjoin-ffi/kotlin/contrib/test.sh

@@ -0,0 +1,15 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+REPO_ROOT="$(cd "$(dirname "$0")/../../.." && pwd)"
+cd "$REPO_ROOT"
+source contrib/lockfile.sh
+use_lockfile Cargo-recent.lock
+
+cd "$REPO_ROOT/payjoin-ffi/kotlin"
+
+echo "==> Generating FFI bindings..."
+bash ./scripts/generate_bindings.sh
+
+echo "==> Running Kotlin tests..."
+./gradlew --no-daemon test

payjoin-ffi/kotlin/gradle.properties

@@ -0,0 +1,2 @@
+org.gradle.jvmargs=-Xmx1g
+kotlin.code.style=official

payjoin-ffi/kotlin/gradle/wrapper/gradle-wrapper.properties

@@ -0,0 +1,8 @@
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-9.1.0-bin.zip
+distributionSha256Sum=a17ddd85a26b6a7f5ddb71ff8b05fc5104c0202c6e64782429790c933686c806
+networkTimeout=10000
+validateDistributionUrl=true
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists