Add C# language bindings for payjoin-ffi

.github/workflows/csharp.yml

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+name: Build and Test CSharp
+on:
+  pull_request:
+    paths:
+      - payjoin-ffi/**
+env:
+  RUSTUP_TOOLCHAIN: 1.85
+
+jobs:
+  build-csharp-and-test:
+    name: "Build and test csharp"
+    runs-on: ${{ matrix.os }}
+    defaults:
+      run:
+        working-directory: payjoin-ffi/csharp
+    strategy:
+      matrix:
+        os: [ubuntu-latest, macos-latest]
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Install Rust 1.85.0
+        uses: dtolnay/[email protected]
+
+      - name: Use cache
+        uses: Swatinem/rust-cache@v2
+
+      - name: Install .NET 8 SDK
+        uses: actions/setup-dotnet@v4
+        with:
+          dotnet-version: "8.0.x"
+
+      - name: Install LLVM (macOS)
+        if: matrix.os == 'macos-latest'
+        run: brew install llvm
+
+      - name: Generate bindings and binaries
+        run: bash ./scripts/generate_bindings.sh
+
+      - name: Run tests
+        run: dotnet test --logger "console;verbosity=minimal"

payjoin-ffi/csharp/.gitignore

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+# Generated bindings
+src/*.cs
+
+# Build outputs
+bin/
+obj/
+
+# IDE
+.vs/
+*.user
+*.suo
+
+# NuGet
+*.nupkg
+packages/
+/lib/*.so
+/lib/*.dylib

payjoin-ffi/csharp/Payjoin.Tests.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net8.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+    <IsPackable>false</IsPackable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.8.0" />
+    <PackageReference Include="xunit" Version="2.6.2" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.5.4">
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+      <PrivateAssets>all</PrivateAssets>
+    </PackageReference>
+  </ItemGroup>
+
+  <!-- Include native library - copied to output directory for testing -->
+  <Target Name="CopyNativeLibraries" AfterTargets="Build">
+    <Copy SourceFiles="lib/libpayjoin_ffi.so" DestinationFolder="$(TargetDir)" Condition="Exists('lib/libpayjoin_ffi.so')" />
+    <Copy SourceFiles="lib/libpayjoin_ffi.dylib" DestinationFolder="$(TargetDir)" Condition="Exists('lib/libpayjoin_ffi.dylib')" />
+  </Target>
+
+</Project>

payjoin-ffi/csharp/README.md

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+# Payjoin C# Bindings
+
+Welcome to the C# language bindings for the [Payjoin Dev Kit](https://payjoindevkit.org/)!
+
+## Running Tests
+
+Follow these steps to clone the repository and run the tests.
+
+```shell
+git clone https://github.com/payjoin/rust-payjoin.git
+cd rust-payjoin/payjoin-ffi/csharp
+
+# Generate the bindings
+bash ./scripts/generate_bindings.sh
+
+# Build the project
+dotnet build
+
+# Run all tests
+dotnet test
+```
+
+## Requirements
+
+- .NET 8.0 or higher
+- `uniffi-bindgen-cs` fork at `chavic/external-types-support` (the `scripts/generate_bindings.sh` script will install it automatically if it's not already on your PATH)
+
+## Configuration
+
+You can specify the path to `uniffi-bindgen-cs` via environment variable:
+```shell
+export UNIFFI_CS=/path/to/uniffi-bindgen-cs
+dotnet build
+```

payjoin-ffi/csharp/UnitTests.cs

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+using Xunit;
+using uniffi.payjoin;
+
+namespace Payjoin.Tests;
+
+public class UriTests
+{
+    [Fact]
+    public void UrlEncodedPayjoinParameter()
+    {
+        var uri = "bitcoin:12c6DSiU4Rq3P4ZxziKxzrL5LmMBrzjrJX?amount=1&pj=https://example.com?ciao";
+        var result = Url.Parse(uri);
+        Assert.NotNull(result);
+    }
+
+    [Fact]
+    public void ValidUrl()
+    {
+        var uri = "bitcoin:12c6DSiU4Rq3P4ZxziKxzrL5LmMBrzjrJX?amount=1&pj=https://example.com?ciao";
+        var result = Url.Parse(uri);
+        Assert.NotNull(result);
+    }
+
+    [Fact]
+    public void MissingAmountShouldBeOk()
+    {
+        var uri = "bitcoin:12c6DSiU4Rq3P4ZxziKxzrL5LmMBrzjrJX?pj=https://testnet.demo.btcpayserver.org/BTC/pj";
+        var result = Url.Parse(uri);
+        Assert.NotNull(result);
+    }
+
+    [Theory]
+    [InlineData("bitcoin:12c6DSiU4Rq3P4ZxziKxzrL5LmMBrzjrJX", "https://example.com")]
+    [InlineData("bitcoin:12c6DSiU4Rq3P4ZxziKxzrL5LmMBrzjrJX", "http://vjdpwgybvubne5hda6v4c5iaeeevhge6jvo3w2cl6eocbwwvwxp7b7qd.onion")]
+    [InlineData("BITCOIN:TB1Q6D3A2W975YNY0ASUVD9A67NER4NKS58FF0Q8G4", "https://example.com")]
+    [InlineData("bitcoin:tb1q6d3a2w975yny0asuvd9a67ner4nks58ff0q8g4", "https://example.com")]
+    public void ValidUrisWithDifferentAddressesAndEndpoints(string address, string pj)
+    {
+        var uri = $"{address}?amount=1&pj={pj}";
+        var result = Url.Parse(uri);
+        Assert.NotNull(result);
+    }
+}
+
+public class InMemoryReceiverPersister : JsonReceiverSessionPersister
+{
+    private List<string> _events = new();
+
+    public void Save(string @event)
+    {
+        _events.Add(@event);
+    }
+
+    public string[] Load()
+    {
+        return _events.ToArray();
+    }
+
+    public void Close()
+    {
+        // no-op for tests
+    }
+}
+
+public class InMemorySenderPersister : JsonSenderSessionPersister
+{
+    private List<string> _events = new();
+
+    public void Save(string @event)
+    {
+        _events.Add(@event);
+    }
+
+    public string[] Load()
+    {
+        return _events.ToArray();
+    }
+
+    public void Close()
+    {
+        // no-op for tests
+    }
+}
+
+public class PersistenceTests
+{
+    private static readonly byte[] OhttpKeysData = new byte[]
+    {
+        0x01, 0x00, 0x16, 0x04, 0xba, 0x48, 0xc4, 0x9c, 0x3d, 0x4a,
+        0x92, 0xa3, 0xad, 0x00, 0xec, 0xc6, 0x3a, 0x02, 0x4d, 0xa1,
+        0x0c, 0xed, 0x02, 0x18, 0x0c, 0x73, 0xec, 0x12, 0xd8, 0xa7,
+        0xad, 0x2c, 0xc9, 0x1b, 0xb4, 0x83, 0x82, 0x4f, 0xe2, 0xbe,
+        0xe8, 0xd2, 0x8b, 0xfe, 0x2e, 0xb2, 0xfc, 0x64, 0x53, 0xbc,
+        0x4d, 0x31, 0xcd, 0x85, 0x1e, 0x8a, 0x65, 0x40, 0xe8, 0x6c,
+        0x53, 0x82, 0xaf, 0x58, 0x8d, 0x37, 0x09, 0x57, 0x00, 0x04,
+        0x00, 0x01, 0x00, 0x03,
+    };
+
+    [Fact]
+    public void ReceiverPersistence()
+    {
+        var persister = new InMemoryReceiverPersister();
+        var address = "tb1q6d3a2w975yny0asuvd9a67ner4nks58ff0q8g4";
+        var ohttpKeys = OhttpKeys.Decode(OhttpKeysData);
+
+        var builder = new ReceiverBuilder(address, "https://example.com", ohttpKeys);
+        var transition = builder.Build();
+        var initialized = transition.Save(persister);
+
+        var result = PayjoinMethods.ReplayReceiverEventLog(persister);
+        var state = result.State();
+
+        Assert.IsType<ReceiveSession.Initialized>(state);
+    }
+
+    [Fact]
+    public void SenderPersistence()
+    {
+        var receiverPersister = new InMemoryReceiverPersister();
+        var address = "2MuyMrZHkbHbfjudmKUy45dU4P17pjG2szK";
+        var ohttpKeys = OhttpKeys.Decode(OhttpKeysData);
+
+        var receiver = new ReceiverBuilder(address, "https://example.com", ohttpKeys)
+            .Build()
+            .Save(receiverPersister);
+        var uri = receiver.PjUri();
+
+        var senderPersister = new InMemorySenderPersister();
+        var psbt = "cHNidP8BAHMCAAAAAY8nutGgJdyYGXWiBEb45Hoe9lWGbkxh/6bNiOJdCDuDAAAAAAD+////AtyVuAUAAAAAF6kUHehJ8GnSdBUOOv6ujXLrWmsJRDCHgIQeAAAAAAAXqRR3QJbbz0hnQ8IvQ0fptGn+votneofTAAAAAAEBIKgb1wUAAAAAF6kU3k4ekGHKWRNbA1rV5tR5kEVDVNCHAQcXFgAUx4pFclNVgo1WWAdN1SYNX8tphTABCGsCRzBEAiB8Q+A6dep+Rz92vhy26lT0AjZn4PRLi8Bf9qoB/CMk0wIgP/Rj2PWZ3gEjUkTlhDRNAQ0gXwTO7t9n+V14pZ6oljUBIQMVmsAaoNWHVMS02LfTSe0e388LNitPa1UQZyOihY+FFgABABYAFEb2Giu6c4KO5YW0pfw3lGp9jMUUAAA=";
+
+        var withReplyKey = new SenderBuilder(psbt, uri)
+            .BuildRecommended(1000)
+            .Save(senderPersister);
+
+        var replayed = PayjoinMethods.ReplaySenderEventLog(senderPersister);
+        var state = replayed.State();
+
+        Assert.IsType<SendSession.WithReplyKey>(state);
+    }
+}
+
+public class ValidationTests
+{
+    private static readonly byte[] OhttpKeysData = new byte[]
+    {
+        0x01, 0x00, 0x16, 0x04, 0xba, 0x48, 0xc4, 0x9c, 0x3d, 0x4a,
+        0x92, 0xa3, 0xad, 0x00, 0xec, 0xc6, 0x3a, 0x02, 0x4d, 0xa1,
+        0x0c, 0xed, 0x02, 0x18, 0x0c, 0x73, 0xec, 0x12, 0xd8, 0xa7,
+        0xad, 0x2c, 0xc9, 0x1b, 0xb4, 0x83, 0x82, 0x4f, 0xe2, 0xbe,
+        0xe8, 0xd2, 0x8b, 0xfe, 0x2e, 0xb2, 0xfc, 0x64, 0x53, 0xbc,
+        0x4d, 0x31, 0xcd, 0x85, 0x1e, 0x8a, 0x65, 0x40, 0xe8, 0x6c,
+        0x53, 0x82, 0xaf, 0x58, 0x8d, 0x37, 0x09, 0x57, 0x00, 0x04,
+        0x00, 0x01, 0x00, 0x03,
+    };
+
+    [Fact]
+    public void ReceiverBuilderRejectsBadAddress()
+    {
+        var ohttpKeys = OhttpKeys.Decode(OhttpKeysData);
+
+        Assert.Throws<ReceiverBuilderException.InvalidAddress>(() =>
+        {
+            new ReceiverBuilder("not-an-address", "https://example.com", ohttpKeys);
+        });
+    }
+
+    [Fact]
+    public void InputPairRejectsInvalidOutpoint()
+    {
+        Assert.Throws<InputPairException.InvalidOutPoint>(() =>
+        {
+            var txin = new PlainTxIn(
+                new PlainOutPoint("deadbeef", 0),
+                new byte[] {},
+                0,
+                new byte[][] {}
+            );
+            var psbtIn = new PlainPsbtInput(null, null, null);
+            new InputPair(txin, psbtIn, null);
+        });
+    }
+}

payjoin-ffi/csharp/scripts/generate_bindings.sh

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+#!/usr/bin/env bash
+set -euo pipefail
+
+OS=$(uname -s)
+echo "Running on $OS"
+
+if [[ $OS == "Darwin" ]]; then
+    LIBNAME=libpayjoin_ffi.dylib
+elif [[ $OS == "Linux" ]]; then
+    LIBNAME=libpayjoin_ffi.so
+else
+    echo "Unsupported os: $OS"
+    exit 1
+fi
+
+# Get the directory where this script is located
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+# Navigate to payjoin-ffi directory (parent of csharp, which is parent of scripts)
+cd "$SCRIPT_DIR/../.."
+
+echo "Generating payjoin C#..."
+cargo build --features _test-utils --profile dev -j2
+
+# Use uniffi-bindgen-cs from the fork/branch we track, installed via cargo (no manual clone).
+UNIFFI_CS=${UNIFFI_CS:-$HOME/.cargo/bin/uniffi-bindgen-cs}
+
+if [[ ! -x "$UNIFFI_CS" ]]; then
+    echo "Installing uniffi-bindgen-cs from https://github.com/chavic/uniffi-bindgen-cs.git#chavic/external-types-support..."
+    cargo install --git https://github.com/chavic/uniffi-bindgen-cs.git --branch chavic/external-types-support --locked uniffi-bindgen-cs
+fi
+
+# Clean output directory to prevent duplicate definitions
+echo "Cleaning csharp/src/ directory..."
+rm -f csharp/src/*.cs
+
+# From payjoin-ffi/, library is at ../target/debug/ (workspace root target)
+$UNIFFI_CS --library ../target/debug/$LIBNAME --out-dir csharp/src/
+
+# UniFFI marks foreign handles via the low bit. Older generators needed a patch to start at 1 and
+# increment by 2. If the expected patterns are missing, assume upstream fixed it and skip.
+python3 - <<'PY'
+from pathlib import Path
+
+path = Path("csharp/src/payjoin.cs")
+text = path.read_text()
+replaced = 0
+
+replacements = [
+    ("ulong currentHandle = 0;", "ulong currentHandle = 1;"),
+    ("currentHandle += 1;\n            map[currentHandle] = obj;\n            return currentHandle;",
+     "var handle = currentHandle;\n            currentHandle += 2;\n            map[handle] = obj;\n            return handle;"),
+]
+
+for old, new in replacements:
+    updated = text.replace(old, new, 1)
+    if updated != text:
+        replaced += 1
+        text = updated
+
+if replaced:
+    path.write_text(text)
+    print(f"Applied handle-map patch ({replaced} replacements).")
+else:
+    print("Handle-map patch not needed (generator already emits odd handles).")
+PY
+
+# Copy native library to csharp/lib/ directory for testing
+echo "Copying native library..."
+mkdir -p csharp/lib
+cp ../target/debug/$LIBNAME csharp/lib/$LIBNAME
+
+echo "All done!"