Implement HTTP client requests for extension queries and downloads with automatic resumable download support

src/c#/ExtensionTest/Services/ExtensionServiceTests.cs

@@ -81,7 +81,7 @@ private List<AvailableExtension> CreateTestExtensions()
         private ExtensionService CreateExtensionService(List<AvailableExtension> extensions)
         {
             var updateQueue = new GeneralUpdate.Extension.Download.UpdateQueue();
-            return new ExtensionService(extensions, "/tmp/test-downloads", updateQueue);
+            return new ExtensionService(extensions, "/tmp/test-downloads", updateQueue, "https://test-server.com/api/extensions");
         }
 
         [Fact]

src/c#/GeneralUpdate.Extension/Examples/ExtensionSystemExample.cs

@@ -21,6 +21,7 @@ public void Initialize()
             var hostVersion = new Version(1, 5, 0);
             var installPath = @"C:\MyApp\Extensions";
             var downloadPath = @"C:\MyApp\Temp\Downloads";
+            var serverUrl = "https://your-server.com/api/extensions";
 
             // Detect current platform
             var currentPlatform = DetectCurrentPlatform();
@@ -31,6 +32,7 @@ public void Initialize()
                 HostVersion = hostVersion,
                 InstallBasePath = installPath,
                 DownloadPath = downloadPath,
+                ServerUrl = serverUrl,
                 TargetPlatform = currentPlatform,
                 DownloadTimeout = 300 // 5 minutes
             };

src/c#/GeneralUpdate.Extension/ExtensionHostConfig.cs

@@ -26,6 +26,13 @@ public class ExtensionHostConfig
         /// </summary>
         public string DownloadPath { get; set; } = null!;
 
+        /// <summary>
+        /// Gets or sets the server URL for extension queries and downloads.
+        /// This is the base URL used to construct Query and Download endpoints.
+        /// Example: "https://your-server.com/api/extensions"
+        /// </summary>
+        public string ServerUrl { get; set; } = null!;
+
         /// <summary>
         /// Gets or sets the target platform (Windows/Linux/macOS).
         /// Defaults to Windows if not specified.
@@ -62,6 +69,8 @@ public void Validate()
                 throw new ArgumentNullException(nameof(InstallBasePath));
             if (string.IsNullOrWhiteSpace(DownloadPath))
                 throw new ArgumentNullException(nameof(DownloadPath));
+            if (string.IsNullOrWhiteSpace(ServerUrl))
+                throw new ArgumentNullException(nameof(ServerUrl));
         }
     }
 }

src/c#/GeneralUpdate.Extension/GeneralExtensionHost.cs

@@ -109,6 +109,7 @@ public GeneralExtensionHost(ExtensionHostConfig config)
                 new List<Metadata.AvailableExtension>(),
                 config.DownloadPath,
                 _updateQueue,
+                config.ServerUrl,
                 config.HostVersion,
                 _validator,
                 config.DownloadTimeout,
@@ -130,6 +131,7 @@ public GeneralExtensionHost(ExtensionHostConfig config)
         /// <param name="hostVersion">The current host application version.</param>
         /// <param name="installBasePath">Base directory for extension installations.</param>
         /// <param name="downloadPath">Directory for downloading extension packages.</param>
+        /// <param name="serverUrl">Server base URL for extension queries and downloads.</param>
         /// <param name="targetPlatform">The current platform (Windows/Linux/macOS).</param>
         /// <param name="downloadTimeout">Download timeout in seconds (default: 300).</param>
         /// <param name="authScheme">Optional HTTP authentication scheme (e.g., "Bearer", "Basic").</param>
@@ -140,6 +142,7 @@ public GeneralExtensionHost(
             Version hostVersion,
             string installBasePath,
             string downloadPath,
+            string serverUrl,
             Metadata.TargetPlatform targetPlatform = Metadata.TargetPlatform.Windows,
             int downloadTimeout = 300,
             string? authScheme = null,
@@ -149,6 +152,7 @@ public GeneralExtensionHost(
                 HostVersion = hostVersion,
                 InstallBasePath = installBasePath,
                 DownloadPath = downloadPath,
+                ServerUrl = serverUrl,
                 TargetPlatform = targetPlatform,
                 DownloadTimeout = downloadTimeout,
                 AuthScheme = authScheme,

src/c#/GeneralUpdate.Extension/Metadata/ExtensionDescriptor.cs

@@ -75,6 +75,9 @@ public class ExtensionDescriptor
 
         /// <summary>
         /// Gets or sets the download URL for the extension package.
+        /// NOTE: This field is optional and primarily for backward compatibility.
+        /// The system constructs download URLs dynamically from the ServerUrl configured in ExtensionHostConfig.
+        /// Format: {ServerUrl}/Download/{ExtensionName}
         /// </summary>
         [JsonPropertyName("downloadUrl")]
         public string? DownloadUrl { get; set; }

src/c#/GeneralUpdate.Extension/README.md

@@ -34,12 +34,17 @@ Note: This library is currently distributed as source. A NuGet package may be av
 using GeneralUpdate.Extension;
 using GeneralUpdate.Extension.Metadata;
 
-// Create extension host
-var host = new ExtensionHost(
-    hostVersion: new Version(1, 0, 0),
-    installPath: @"C:\MyApp\Extensions",
-    downloadPath: @"C:\MyApp\Downloads",
-    targetPlatform: TargetPlatform.Windows);
+// Create extension host with configuration
+var config = new ExtensionHostConfig
+{
+    HostVersion = new Version(1, 0, 0),
+    InstallBasePath = @"C:\MyApp\Extensions",
+    DownloadPath = @"C:\MyApp\Downloads",
+    ServerUrl = "https://your-server.com/api/extensions",
+    TargetPlatform = TargetPlatform.Windows
+};
+
+var host = new GeneralExtensionHost(config);
 
 // Load installed extensions
 host.LoadInstalledExtensions();
@@ -54,6 +59,32 @@ host.UpdateStateChanged += (sender, args) =>
 var installed = host.GetInstalledExtensions();
 ```
 
+## Server URL Architecture
+
+The extension system uses a server-based architecture for querying and downloading extensions. The `ServerUrl` configured in `ExtensionHostConfig` serves as the base URL for all extension operations.
+
+### URL Construction
+
+The system automatically constructs the following endpoints:
+
+- **Query Endpoint**: `{ServerUrl}/Query` - Used for searching and filtering extensions
+- **Download Endpoint**: `{ServerUrl}/Download/{ExtensionName}` - Used for downloading extension packages
+
+### Example
+
+If your `ServerUrl` is `https://your-server.com/api/extensions`:
+- Query endpoint: `https://your-server.com/api/extensions/Query`
+- Download for extension "my-extension": `https://your-server.com/api/extensions/Download/my-extension`
+
+### Server Requirements
+
+Your server should implement these endpoints:
+
+1. **Query Endpoint** - Returns available extensions based on filter criteria
+2. **Download Endpoint** - Returns the extension package file (typically .zip format)
+
+The `DownloadUrl` field in extension descriptors is now optional and primarily for backward compatibility. The system constructs download URLs dynamically from the configured ServerUrl.
+
 ## Complete Usage Guide
 
 ### 1. Dependency Injection Setup
@@ -70,25 +101,29 @@ public class YourModule : IModule
 {
     public void RegisterTypes(IContainerRegistry containerRegistry)
     {
-        var hostVersion = new Version(1, 0, 0);
-        var installPath = @"C:\MyApp\Extensions";
-        var downloadPath = @"C:\MyApp\Downloads";
-        var platform = Metadata.TargetPlatform.Windows;
+        var config = new ExtensionHostConfig
+        {
+            HostVersion = new Version(1, 0, 0),
+            InstallBasePath = @"C:\MyApp\Extensions",
+            DownloadPath = @"C:\MyApp\Downloads",
+            ServerUrl = "https://your-server.com/api/extensions",
+            TargetPlatform = Metadata.TargetPlatform.Windows
+        };
 
         // Register as singletons
         containerRegistry.RegisterSingleton<Core.IExtensionCatalog>(() => 
-            new Core.ExtensionCatalog(installPath));
+            new Core.ExtensionCatalog(config.InstallBasePath));
 
         containerRegistry.RegisterSingleton<Compatibility.ICompatibilityValidator>(() => 
-            new Compatibility.CompatibilityValidator(hostVersion));
+            new Compatibility.CompatibilityValidator(config.HostVersion));
 
         containerRegistry.RegisterSingleton<Download.IUpdateQueue, Download.UpdateQueue>();
 
         containerRegistry.RegisterSingleton<PackageGeneration.IExtensionPackageGenerator, 
             PackageGeneration.ExtensionPackageGenerator>();
 
         containerRegistry.RegisterSingleton<IExtensionHost>(() => 
-            new ExtensionHost(hostVersion, installPath, downloadPath, platform));
+            new GeneralExtensionHost(config));
     }
 }
 
@@ -102,24 +137,28 @@ var host = container.Resolve<IExtensionHost>();
 using Microsoft.Extensions.DependencyInjection;
 
 var services = new ServiceCollection();
-var hostVersion = new Version(1, 0, 0);
-var installPath = @"C:\Extensions";
-var downloadPath = @"C:\Downloads";
+var config = new ExtensionHostConfig
+{
+    HostVersion = new Version(1, 0, 0),
+    InstallBasePath = @"C:\Extensions",
+    DownloadPath = @"C:\Downloads",
+    ServerUrl = "https://your-server.com/api/extensions",
+    TargetPlatform = Metadata.TargetPlatform.Windows
+};
 
 services.AddSingleton<Core.IExtensionCatalog>(sp => 
-    new Core.ExtensionCatalog(installPath));
+    new Core.ExtensionCatalog(config.InstallBasePath));
 
 services.AddSingleton<Compatibility.ICompatibilityValidator>(sp => 
-    new Compatibility.CompatibilityValidator(hostVersion));
+    new Compatibility.CompatibilityValidator(config.HostVersion));
 
 services.AddSingleton<Download.IUpdateQueue, Download.UpdateQueue>();
 
 services.AddSingleton<PackageGeneration.IExtensionPackageGenerator, 
     PackageGeneration.ExtensionPackageGenerator>();
 
 services.AddSingleton<IExtensionHost>(sp => 
-    new ExtensionHost(hostVersion, installPath, downloadPath, 
-        Metadata.TargetPlatform.Windows));
+    new GeneralExtensionHost(config));
 
 var provider = services.BuildServiceProvider();
 var host = provider.GetRequiredService<IExtensionHost>();
@@ -128,11 +167,16 @@ var host = provider.GetRequiredService<IExtensionHost>();
 #### Without DI (Direct Instantiation)
 
 ```csharp
-var host = new ExtensionHost(
-    new Version(1, 0, 0),
-    @"C:\Extensions",
-    @"C:\Downloads",
-    Metadata.TargetPlatform.Windows);
+var config = new ExtensionHostConfig
+{
+    HostVersion = new Version(1, 0, 0),
+    InstallBasePath = @"C:\Extensions",
+    DownloadPath = @"C:\Downloads",
+    ServerUrl = "https://your-server.com/api/extensions",
+    TargetPlatform = Metadata.TargetPlatform.Windows
+};
+
+var host = new GeneralExtensionHost(config);
 ```
 
 ### 2. Loading and Managing Extensions