adding compile-time const whether to use the broker service

src/Runner.Common/BrokerServer.cs

@@ -0,0 +1,38 @@
+using System;
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
+using GitHub.Runner.Common.Util;
+using GitHub.Services.WebApi;
+using GitHub.Services.Common;
+using GitHub.Runner.Sdk;
+using System.Net.Http;
+
+namespace GitHub.Runner.Common
+{
+    [ServiceLocator(Default = typeof(BrokerServer))]
+    public interface IBrokerServer : IRunnerService
+    {
+        Task ConnectAsync(Uri serverUrl, CancellationToken cancellationToken);
+        Task<GitHub.DistributedTask.WebApi.TaskAgentMessage> GetMessageAsync(Int32 poolId, Guid sessionId, Int64? lastMessageId, CancellationToken cancellationToken);
+    }
+
+    public sealed class BrokerServer : RunnerService, IBrokerServer
+    {
+        private HttpClient _httpClient;
+
+        public async Task ConnectAsync(Uri serverUrl, CancellationToken cancellationToken)
+        {
+            _httpClient = new HttpClient();
+            _httpClient.BaseAddress = serverUrl;
+            _httpClient.Timeout = TimeSpan.FromSeconds(100);
+            await _httpClient.GetAsync("health", cancellationToken);
+        }
+
+        public async Task<GitHub.DistributedTask.WebApi.TaskAgentMessage> GetMessageAsync(Int32 poolId, Guid sessionId, Int64? lastMessageId, CancellationToken cancellationToken)
+        {
+            await _httpClient.GetAsync("message", cancellationToken);
+            return null;
+        }
+    }
+}