rework how we fetch plugins from manifest URLs

Introduces the concept of a store of community plugins, which is currently
limited to the official PluginsManifest repository.

Each store can support more than one manifest file URLs. When fetching, all
URLs are used until one of them succeeds. This fixes issues with geo-blocking
such as #2195

Plugin stores can be expanded in the future to be user-configurable, see #2178

Author: JohnTheGr8

Flow.Launcher.Core/ExternalPlugins/CommunityPluginSource.cs

@@ -0,0 +1,59 @@
+using Flow.Launcher.Infrastructure.Http;
+using Flow.Launcher.Infrastructure.Logger;
+using System;
+using System.Collections.Generic;
+using System.Net;
+using System.Net.Http;
+using System.Text.Json;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace Flow.Launcher.Core.ExternalPlugins
+{
+    public record CommunityPluginSource(string ManifestFileUrl)
+    {
+        private string latestEtag = "";
+
+        private List<UserPlugin> plugins = new();
+
+        /// <summary>
+        /// Fetch and deserialize the contents of a plugins.json file found at <see cref="ManifestFileUrl"/>.
+        /// We use conditional http requests to keep repeat requests fast.
+        /// </summary>
+        /// <remarks>
+        /// This method will only return plugin details when the underlying http request is successful (200 or 304).
+        /// In any other case, an exception is raised
+        /// </remarks>
+        public async Task<List<UserPlugin>> FetchAsync(CancellationToken token)
+        {
+            Log.Info(nameof(CommunityPluginSource), $"Loading plugins from {ManifestFileUrl}");
+
+            var request = new HttpRequestMessage(HttpMethod.Get, ManifestFileUrl);
+
+            request.Headers.Add("If-None-Match", latestEtag);
+
+            using var response = await Http.SendAsync(request, HttpCompletionOption.ResponseHeadersRead, token).ConfigureAwait(false);
+
+            if (response.StatusCode == HttpStatusCode.OK)
+            {
+                await using var json = await response.Content.ReadAsStreamAsync(token).ConfigureAwait(false);
+
+                this.plugins = await JsonSerializer.DeserializeAsync<List<UserPlugin>>(json, cancellationToken: token).ConfigureAwait(false);
+                this.latestEtag = response.Headers.ETag.Tag;
+
+                Log.Info(nameof(CommunityPluginSource), $"Loaded {this.plugins.Count} plugins from {ManifestFileUrl}");
+                return this.plugins;
+            }
+            else if (response.StatusCode == HttpStatusCode.NotModified)
+            {
+                Log.Info(nameof(CommunityPluginSource), $"Resource {ManifestFileUrl} has not been modified.");
+                return this.plugins;
+            }
+            else
+            {
+                Log.Warn(nameof(CommunityPluginSource), $"Failed to load resource {ManifestFileUrl} with response {response.StatusCode}");
+                throw new Exception($"Failed to load resource {ManifestFileUrl} with response {response.StatusCode}");
+            }
+        }
+    }
+}

Flow.Launcher.Core/ExternalPlugins/CommunityPluginStore.cs

@@ -0,0 +1,54 @@
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace Flow.Launcher.Core.ExternalPlugins
+{
+    /// <summary>
+    /// Describes a store of community-made plugins.
+    /// The provided URLs should point to a json file, whose content
+    /// is deserializable as a <see cref="UserPlugin"/> array.
+    /// </summary>
+    /// <param name="primaryUrl">Primary URL to the manifest json file.</param>
+    /// <param name="secondaryUrls">Secondary URLs to access the <paramref name="primaryUrl"/>, for example CDN links</param>
+    public record CommunityPluginStore(string primaryUrl, params string[] secondaryUrls)
+    {
+        private readonly List<CommunityPluginSource> pluginSources =
+            secondaryUrls
+                .Append(primaryUrl)
+                .Select(url => new CommunityPluginSource(url))
+                .ToList();
+
+        public async Task<List<UserPlugin>> FetchAsync(CancellationToken token)
+        {
+            // we create a new cancellation token source linked to the given token.
+            // Once any of the http requests completes successfully, we call cancel
+            // to stop the rest of the running http requests.
+            var cts = CancellationTokenSource.CreateLinkedTokenSource(token);
+
+            var tasks = pluginSources
+                .Select(pluginSource => pluginSource.FetchAsync(cts.Token))
+                .ToList();
+
+            var pluginResults = new List<UserPlugin>();
+
+            // keep going until all tasks have completed
+            while (tasks.Any())
+            {
+                var completedTask = await Task.WhenAny(tasks);
+                if (completedTask.IsCompletedSuccessfully)
+                {
+                    // one of the requests completed successfully; keep its results
+                    // and cancel the remaining http requests.
+                    pluginResults = await completedTask;
+                    cts.Cancel();
+                }
+                tasks.Remove(completedTask);
+            }
+
+            // all tasks have finished
+            return pluginResults;
+        }
+    }
+}

Flow.Launcher.Core/ExternalPlugins/PluginsManifest.cs

@@ -1,50 +1,30 @@
-using Flow.Launcher.Infrastructure.Http;
-using Flow.Launcher.Infrastructure.Logger;
+using Flow.Launcher.Infrastructure.Logger;
 using System;
 using System.Collections.Generic;
-using System.Net;
-using System.Net.Http;
-using System.Text.Json;
 using System.Threading;
 using System.Threading.Tasks;
 
 namespace Flow.Launcher.Core.ExternalPlugins
 {
     public static class PluginsManifest
     {
-        private const string manifestFileUrl = "https://cdn.jsdelivr.net/gh/Flow-Launcher/Flow.Launcher.PluginsManifest@plugin_api_v2/plugins.json";
+        private static readonly CommunityPluginStore mainPluginStore =
+            new("https://raw.githubusercontent.com/Flow-Launcher/Flow.Launcher.PluginsManifest/plugin_api_v2/plugins.json",
+                "https://cdn.jsdelivr.net/gh/Flow-Launcher/Flow.Launcher.PluginsManifest@plugin_api_v2/plugins.json");
 
         private static readonly SemaphoreSlim manifestUpdateLock = new(1);
 
-        private static string latestEtag = "";
-
-        public static List<UserPlugin> UserPlugins { get; private set; } = new List<UserPlugin>();
+        public static List<UserPlugin> UserPlugins { get; private set; }
 
         public static async Task UpdateManifestAsync(CancellationToken token = default)
         {
             try
             {
                 await manifestUpdateLock.WaitAsync(token).ConfigureAwait(false);
 
-                var request = new HttpRequestMessage(HttpMethod.Get, manifestFileUrl);
-                request.Headers.Add("If-None-Match", latestEtag);
-
-                using var response = await Http.SendAsync(request, HttpCompletionOption.ResponseHeadersRead, token).ConfigureAwait(false);
-
-                if (response.StatusCode == HttpStatusCode.OK)
-                {
-                    Log.Info($"|PluginsManifest.{nameof(UpdateManifestAsync)}|Fetched plugins from manifest repo");
-
-                    await using var json = await response.Content.ReadAsStreamAsync(token).ConfigureAwait(false);
-
-                    UserPlugins = await JsonSerializer.DeserializeAsync<List<UserPlugin>>(json, cancellationToken: token).ConfigureAwait(false);
+                var results = await mainPluginStore.FetchAsync(token).ConfigureAwait(false);
 
-                    latestEtag = response.Headers.ETag.Tag;
-                }
-                else if (response.StatusCode != HttpStatusCode.NotModified)
-                {
-                    Log.Warn($"|PluginsManifest.{nameof(UpdateManifestAsync)}|Http response for manifest file was {response.StatusCode}");
-                }
+                UserPlugins = results;
             }
             catch (Exception e)
             {