Extract Mono runtime builds from each Unity version

.gitignore

@@ -7,3 +7,5 @@ config.toml
 data/
 .idea
 *.user
+.vs/
+launchSettings.json

UnityDataMiner/DownloadableAssetCollection.cs

@@ -0,0 +1,64 @@
+using AssetRipper.Primitives;
+using Serilog;
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Net.Sockets;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace UnityDataMiner
+{
+    internal class DownloadableAssetCollection
+    {
+        // url -> path
+        private readonly Dictionary<string, string> assets = new();
+
+        // returns actual asset path
+        public string AddAsset(string url, string destPath)
+        {
+            if (!assets.TryGetValue(url, out var realPath))
+            {
+                assets.Add(url, realPath = destPath);
+            }
+
+            return realPath;
+        }
+
+        public async Task DownloadAssetsAsync(Func<string, string, CancellationToken, Task> downloadFunc, UnityVersion version,
+            SemaphoreSlim? downloadLock = null, CancellationToken cancellationToken = default)
+        {
+            while (true)
+            {
+                try
+                {
+                    if (downloadLock is not null)
+                    {
+                        await downloadLock.WaitAsync(cancellationToken);
+                    }
+                    try
+                    {
+                        foreach (var (url, dest) in assets)
+                        {
+                            await downloadFunc(url, dest, cancellationToken);
+                        }
+                    }
+                    finally
+                    {
+                        if (!cancellationToken.IsCancellationRequested && downloadLock is not null)
+                        {
+                            downloadLock.Release();
+                        }
+                    }
+
+                    break;
+                }
+                catch (IOException e) when (e.InnerException is SocketException { SocketErrorCode: SocketError.ConnectionReset })
+                {
+                    Log.Warning("Failed to download {Version}, waiting 5 seconds before retrying...", version);
+                    await Task.Delay(5000, cancellationToken);
+                }
+            }
+        }
+    }
+}