Add Velopack Flow update source

src/Velopack/Sources/VelopackFlowUpdateSource.cs

@@ -0,0 +1,89 @@
+using System;
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.Extensions.Logging;
+using Velopack.Json;
+using Velopack.Locators;
+
+namespace Velopack.Sources
+{
+    /// <summary>
+    /// Retrieves updates from the hosted Velopack service. 
+    /// </summary>
+    public sealed class VelopackFlowUpdateSource : IUpdateSource
+    {
+        /// <inheritdoc cref="SimpleWebSource" />
+        public VelopackFlowUpdateSource(
+            string baseUri = "https://api.velopack.io/",
+            IFileDownloader? downloader = null)
+        {
+            BaseUri = new Uri(baseUri);
+            Downloader = downloader ?? Utility.CreateDefaultDownloader();
+        }
+
+        /// <summary> The URL of the server hosting packages to update to. </summary>
+        public Uri BaseUri { get; }
+
+        /// <summary> The <see cref="IFileDownloader"/> to be used for performing http requests. </summary>
+        public IFileDownloader Downloader { get; }
+
+        /// <inheritdoc />
+        public async Task<VelopackAssetFeed> GetReleaseFeed(ILogger logger, string channel, Guid? stagingId = null, 
+            VelopackAsset? latestLocalRelease = null)
+        {
+            Uri baseUri = new(BaseUri, $"api/v1.0/manifest/");
+            var uri = Utility.AppendPathToUri(baseUri, Utility.GetVeloReleaseIndexName(channel));
+            var args = new Dictionary<string, string>();
+
+            if (VelopackRuntimeInfo.SystemArch != RuntimeCpu.Unknown) {
+                args.Add("arch", VelopackRuntimeInfo.SystemArch.ToString());
+            }
+
+            if (VelopackRuntimeInfo.SystemOs != RuntimeOs.Unknown) {
+                args.Add("os", VelopackRuntimeInfo.SystemOs.GetOsShortName());
+                args.Add("rid", VelopackRuntimeInfo.SystemRid);
+            }
+
+            if (latestLocalRelease != null) {
+                args.Add("id", latestLocalRelease.PackageId);
+                args.Add("localVersion", latestLocalRelease.Version.ToString());
+            } else {
+                args.Add("id", VelopackLocator.GetDefault(logger).AppId ?? "");
+            }
+
+            var uriAndQuery = Utility.AddQueryParamsToUri(uri, args);
+
+            logger.Info($"Downloading releases from '{uriAndQuery}'.");
+
+            var json = await Downloader.DownloadString(uriAndQuery.ToString()).ConfigureAwait(false);
+
+            var releaseAssets = SimpleJson.DeserializeObject<VelopackReleaseAsset[]>(json);
+            return new VelopackAssetFeed() {
+                Assets = releaseAssets
+            };
+        }
+
+        /// <inheritdoc />
+        public async Task DownloadReleaseEntry(ILogger logger, VelopackAsset releaseEntry, string localFile, Action<int> progress, CancellationToken cancelToken = default)
+        {
+            if (releaseEntry is null) throw new ArgumentNullException(nameof(releaseEntry));
+            if (releaseEntry is not VelopackReleaseAsset velopackRelease) {
+                throw new ArgumentException($"Expected {nameof(releaseEntry)} to be {nameof(VelopackReleaseAsset)} but was {releaseEntry.GetType().FullName}");
+            }
+            if (localFile is null) throw new ArgumentNullException(nameof(localFile));
+
+            Uri sourceBaseUri = Utility.EnsureTrailingSlash(BaseUri);
+
+            Uri downloadUri = new(sourceBaseUri, $"api/v1.0/download/{velopackRelease.Id}");
+
+            logger.Info($"Downloading '{releaseEntry.FileName}' from '{downloadUri}'.");
+            await Downloader.DownloadFile(downloadUri.AbsoluteUri, localFile, progress, cancelToken: cancelToken).ConfigureAwait(false);
+        }
+    }
+
+    internal record VelopackReleaseAsset : VelopackAsset
+    {
+        public string? Id { get; init; }
+    }
+}