Adapt payjoin implementation to the BIP (#1569)

BTCPayServer.Tests/FakeServer.cs

@@ -0,0 +1,74 @@
+using System.Threading.Channels;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Net.Http;
+using System.Text;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.Hosting;
+using Microsoft.AspNetCore.Hosting.Server.Features;
+using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Hosting;
+
+namespace BTCPayServer.Tests
+{
+    public class FakeServer : IDisposable
+    {
+        IWebHost webHost;
+        SemaphoreSlim semaphore;
+        CancellationTokenSource cts = new CancellationTokenSource();
+        public FakeServer()
+        {
+            _channel = Channel.CreateUnbounded<HttpContext>();
+            semaphore = new SemaphoreSlim(0);
+        }
+
+        Channel<HttpContext> _channel;
+        public async Task Start()
+        {
+            webHost = new WebHostBuilder()
+                    .UseKestrel()
+                    .UseUrls("http://127.0.0.1:0")
+                    .Configure(appBuilder =>
+                    {
+                        appBuilder.Run(async ctx =>
+                        {
+                            await _channel.Writer.WriteAsync(ctx);
+                            await semaphore.WaitAsync(cts.Token);
+                        });
+                    })
+                    .Build();
+            await webHost.StartAsync();
+            var port = new Uri(webHost.ServerFeatures.Get<IServerAddressesFeature>().Addresses.First(), UriKind.Absolute)
+                .Port;
+            ServerUri = new Uri($"http://127.0.0.1:{port}/");
+        }
+
+        public Uri ServerUri { get; set; }
+
+        public void Done()
+        {
+            semaphore.Release();
+        }
+
+        public async Task Stop()
+        {
+            await webHost.StopAsync();
+        }
+        public void Dispose()
+        {
+            cts.Dispose();
+            webHost?.Dispose();
+            semaphore.Dispose();
+        }
+
+        public async Task<HttpContext> GetNextRequest()
+        {
+            return await _channel.Reader.ReadAsync();
+        }
+    }
+}