✨ Gateway proxy for contained frontend to access other services

DysonNetwork.Shared/DysonNetwork.Shared.csproj

@@ -29,6 +29,7 @@
         <PackageReference Include="NodaTime.Serialization.SystemTextJson" Version="1.3.0" />
         <PackageReference Include="StackExchange.Redis" Version="2.8.41" />
         <PackageReference Include="System.Net.Http" Version="4.3.4" />
+        <PackageReference Include="Yarp.ReverseProxy" Version="2.3.0" />
     </ItemGroup>
 
     <ItemGroup>

DysonNetwork.Shared/Registry/GatewayReverseProxy.cs

@@ -0,0 +1,83 @@
+using System.Diagnostics;
+using System.Net;
+using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.Http;
+using Microsoft.Extensions.DependencyInjection;
+using Yarp.ReverseProxy.Forwarder;
+
+namespace DysonNetwork.Shared.Registry;
+
+public static class GatewayReverseProxy
+{
+    /// <summary>
+    /// Provides reverse proxy for DysonNetwork.Gateway.
+    /// Give the ability to the contained frontend to access other services via the gateway.
+    /// </summary>
+    /// <param name="app">The asp.net core application</param>
+    /// <returns>The modified application</returns>
+    public static WebApplication MapGatewayProxy(this WebApplication app)
+    {
+        var httpClient = new HttpMessageInvoker(new SocketsHttpHandler
+        {
+            UseProxy = false,
+            AllowAutoRedirect = true,
+            AutomaticDecompression = DecompressionMethods.All,
+            UseCookies = true,
+            EnableMultipleHttp2Connections = true,
+            ActivityHeadersPropagator = new ReverseProxyPropagator(DistributedContextPropagator.Current),
+            ConnectTimeout = TimeSpan.FromSeconds(15),
+        });
+
+        var transformer = new GatewayReverseProxyTransformer();
+        var requestConfig = new ForwarderRequestConfig();
+
+        app.Map("/cgi/{**catch-all}", async (HttpContext context, IHttpForwarder forwarder) =>
+        {
+            var registry = context.RequestServices.GetRequiredService<ServiceRegistry>();
+            var gatewayUrl = await registry.GetServiceUrl("DysonNetwork.Gateway");
+            if (gatewayUrl is null)
+            {
+                context.Response.StatusCode = 404;
+                await context.Response.WriteAsync("Gateway not found");
+                return;
+            }
+
+            var error = await forwarder.SendAsync(
+                context,
+                gatewayUrl,
+                httpClient,
+                requestConfig,
+                transformer
+            );
+            if (error != ForwarderError.None)
+            {
+                var errorFeature = context.GetForwarderErrorFeature();
+                var exception = errorFeature?.Exception;
+                context.Response.StatusCode = 502;
+                context.Response.ContentType = "text/plain";
+                await context.Response.WriteAsync($"Gateway remote error: {exception?.Message}");
+            }
+        });
+
+        return app;
+    }
+}
+
+public class GatewayReverseProxyTransformer : HttpTransformer
+{
+    private const string Value = "/cgi";
+    
+    public override ValueTask TransformRequestAsync(
+        HttpContext httpContext,
+        HttpRequestMessage proxyRequest,
+        string destinationPrefix,
+        CancellationToken cancellationToken
+    )
+    {
+        httpContext.Request.Path = httpContext.Request.Path.StartsWithSegments(Value, out var remaining)
+            ? remaining
+            : httpContext.Request.Path;
+        
+        return Default.TransformRequestAsync(httpContext, proxyRequest, destinationPrefix, cancellationToken);
+    }
+}

DysonNetwork.Shared/Registry/ServiceInjectionHelper.cs

@@ -5,7 +5,7 @@ using Microsoft.Extensions.DependencyInjection;
 
 namespace DysonNetwork.Shared.Registry;
 
-public static class ServiceHelper
+public static class ServiceInjectionHelper
 {
     public static IServiceCollection AddPusherService(this IServiceCollection services)
     {

DysonNetwork.Shared/Registry/ServiceRegistry.cs

@@ -45,4 +45,11 @@ public class ServiceRegistry(IEtcdClient etcd, ILogger<ServiceRegistry> logger)
         var key = $"/services/{serviceName}";
         await etcd.DeleteAsync(key);
     }
+
+    public async Task<string?> GetServiceUrl(string serviceName)
+    {
+        var key = $"/services/{serviceName}";
+        var response = await etcd.GetAsync(key);
+        return response.Kvs.Count == 0 ? null : response.Kvs[0].Value.ToStringUtf8();
+    }
 }

DysonNetwork.Shared/Registry/Startup.cs

@@ -8,7 +8,8 @@ public static class RegistryStartup
 {
     public static IServiceCollection AddRegistryService(
         this IServiceCollection services,
-        IConfiguration configuration
+        IConfiguration configuration,
+        bool addForwarder = true
     )
     {
         services.AddEtcdClient(options =>
@@ -19,6 +20,9 @@ public static class RegistryStartup
         services.AddSingleton<ServiceRegistry>();
         services.AddHostedService<RegistryHostedService>();
 
+        if (addForwarder)
+            services.AddHttpForwarder();
+
         return services;
     }
 }