Adding KeepAliveInterval option and settings for ctrl channel

CONFIG.md

@@ -254,6 +254,14 @@ file.
 The connection string can be set via the AZURE_BRIDGE_CONNECTIONSTRING
 environment variable. 
 
+### **-a keepalive_interval**
+
+Specifies the interval (in seconds) between keepalive messages sent on the
+"control connection" through which the listener accepts new connections.
+The default is 30 seconds. The value is the maximum interval during which
+a disconnected listener can go unnoticed by the remote forwarder and the
+automatic reconnection mechanism is triggered.
+
 ### -h
 
 **-?**
@@ -325,6 +333,11 @@ the -L and -T command line options above.
   should bind local port forwardings to the wildcard address, thus allowing remote 
   hosts to connect to forwarded ports. The argument must be "true" or "false".  
   The default is "false". 
+* **KeepAliveInterval** - Specifies the interval (in seconds) between keepalive
+  messages sent on the "control connection" through which the listener accepts
+  new connections.  The default is 30 seconds. The value is the maximum interval
+  during which a disconnected listener can go unnoticed by the remote forwarder and
+  the automatic reconnection mechanism is triggered.
 * **LocalForward** - Specifies that a (set of) TCP ports on the local machine 
   shall be forwarded via the Azure Relay. Each entry can have four properties,
   "BindAddress", "Port", "LocalSocket", and "RelayName". See [below](#localforward-properties) for 

src/Microsoft.Azure.Relay.Bridge/Configuration/CommandLineSettings.cs

@@ -22,6 +22,8 @@ public class CommandLineSettings
 #endif
         [Option(CommandOptionType.NoValue, LongName = "svc", ShortName = "svc", Description = "Reserved for background service invocation")]
         public bool? ServiceRun { get; set; }
+        [Option(CommandOptionType.SingleValue, ShortName = "a", Description = "Keepalive interval in seconds (default 30)")]
+        public int? KeepAliveInterval { get; set; }
         [Option(CommandOptionType.SingleValue, ShortName = "b", Description = "Source address of forwarding connections.")]
         public string BindAddress { get; set; }
         [Option(CommandOptionType.SingleValue, ShortName = "e", Description = "Relay endpoint URI")]

src/Microsoft.Azure.Relay.Bridge/Configuration/Config.cs

@@ -432,6 +432,16 @@ public string LogFileName
             }
         }
 
+        /// <summary>
+        /// Specifies the number of seconds that the control connection to the
+        /// Azure Relay server may be inactive before it is "pinged" and therefore 
+        /// checked. The default is 30 seconds. You can specify a shorter interval 
+        /// if you are using a problematic network that disconnects idle connections 
+        /// frequently. The value is the maximum number of seconds that a disconnected
+        /// listener will go undetected.
+        /// </summary>
+        public int KeepAliveInterval { get; set; } = 30;
+
         /// <summary>
         /// Specifies that a TCP port on the remote machine be bound to 
         /// a name on the Azure Relay.
@@ -573,6 +583,10 @@ public static Config LoadConfig(CommandLineSettings commandLineSettings)
             {
                 config.AzureRelayConnectionString = commandLineSettings.ConnectionString;
             }
+            if (commandLineSettings.KeepAliveInterval.HasValue)
+            {
+                config.KeepAliveInterval = commandLineSettings.KeepAliveInterval.Value;
+            }
 
             if (commandLineSettings.LocalForward != null)
             {
@@ -1132,6 +1146,10 @@ private void Merge(Config otherConfig)
             {
                 this.LogLevel = otherConfig.LogLevel;
             }
+            if (otherConfig.KeepAliveInterval != 30)
+            {
+                this.KeepAliveInterval = otherConfig.KeepAliveInterval;
+            }
 
             if (this.ClearAllForwardings.HasValue && this.ClearAllForwardings.Value)
             {

src/Microsoft.Azure.Relay.Bridge/RemoteForwardBridge.cs

@@ -86,6 +86,7 @@ public async Task Open()
             {
                 this.listener = new HybridConnectionListener(connectionString.ToString());
             }
+            this.listener.KeepAliveInterval = TimeSpan.FromSeconds(config.KeepAliveInterval);
             this.listener.Online += (s, e) => { Online?.Invoke(this, e); };
             this.listener.Offline += (s, e) => { Offline?.Invoke(this, e); };
             this.listener.Connecting += (s, e) => { Connecting?.Invoke(this, e); };

test/unit/Microsoft.Azure.Relay.Bridge.Tests/ConfigTest.cs

@@ -52,7 +52,8 @@ string CreateMaxCommandLine()
                    " -H baz5:http/service.example.com" +
                    " -H abc/def:http/service.example.com/foo" +
                    " -H ghi/jkl:http/service1.example.com/foo;http/service2.example.com/foo" +
-                   " -v";
+                   " -v" +
+                   " -a 60";
         }
 
         string CreateMaxConfig()
@@ -69,6 +70,7 @@ string CreateMaxConfig()
                         "ClearAllForwardings : false " + textWriter.NewLine +
                         "ConnectionAttempts : 1 " + textWriter.NewLine +
                         "ConnectTimeout : 60 " + textWriter.NewLine +
+                        "KeepAliveInterval : 60 " + textWriter.NewLine +
                         "ExitOnForwardFailure : true " + textWriter.NewLine +
                         "LocalForward : " + textWriter.NewLine +
                         "  - BindAddress : 127.0.100.1" + textWriter.NewLine +
@@ -700,6 +702,7 @@ public void ConfigBadConnectTimeoutTest()
         }
         private static void CheckMaxCommandLine(Config config)
         {
+            Assert.Equal(60, config.KeepAliveInterval);
             Assert.Equal("Endpoint=sb://cvrelay.servicebus.windows.net/;SharedAccessKeyName=send;SharedAccessKey=abcdefgh;", config.AzureRelayConnectionString);
             Assert.Equal("sb://cvrelay.servicebus.windows.net/", config.AzureRelayEndpoint);
             Assert.Equal("send", config.AzureRelaySharedAccessKeyName);
@@ -778,6 +781,7 @@ private static void CheckMaxCommandLine(Config config)
 
         private static void CheckMaxConfig(Config config)
         {
+            Assert.Equal(60, config.KeepAliveInterval);
             Assert.Equal("inet", config.AddressFamily);
             Assert.Equal("Endpoint=sb://cvrelay.servicebus.windows.net/;SharedAccessKeyName=RootManageSharedAccessKey;SharedAccessKey=P0CQgKxRl8S0ABAlmbitHDEWfwWUQzKB34J0w48SB/w=;", config.AzureRelayConnectionString);
             Assert.Equal("sb://cvrelay.servicebus.windows.net/", config.AzureRelayEndpoint);