Use next available port when default port is used

Author: PramodValavala-MSFT

src/Azure.Functions.Cli/Actions/HostActions/StartHostAction.cs

@@ -91,7 +91,7 @@ public override ICommandLineParserResult ParseArgs(string[] args)
             Parser
                 .Setup<int>('p', "port")
                 .WithDescription($"Local port to listen on. Default: {DefaultPort}")
-                .SetDefault(hostSettings.LocalHttpPort == default(int) ? DefaultPort : hostSettings.LocalHttpPort)
+                .SetDefault(hostSettings.LocalHttpPort == default(int) ? NetworkHelpers.GetNextAvailablePort(DefaultPort) : hostSettings.LocalHttpPort)
                 .Callback(p => Port = p);
 
             Parser

src/Azure.Functions.Cli/Helpers/NetworkHelpers.cs

@@ -1,4 +1,8 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
 using System.Net;
+using System.Net.NetworkInformation;
 using System.Net.Sockets;
 
 namespace Azure.Functions.Cli.Helpers
@@ -33,5 +37,33 @@ public static int GetAvailablePort()
                 listener.Stop();
             }
         }
+
+        public static int GetNextAvailablePort(int startPort)
+        {
+            var usedPorts = new List<int>();
+            var ipGlobalProperties = IPGlobalProperties.GetIPGlobalProperties();
+
+            usedPorts.AddRange(ipGlobalProperties
+                                .GetActiveTcpConnections()
+                                .Where(c => c.LocalEndPoint.Port >= startPort)
+                                .Select(c => c.LocalEndPoint.Port));
+            usedPorts.AddRange(ipGlobalProperties
+                                .GetActiveTcpListeners()
+                                .Where(l => l.Port >= startPort)
+                                .Select(l => l.Port));
+
+            usedPorts.Sort();
+
+            foreach (var usedPort in usedPorts)
+            {
+                if (startPort < usedPort)
+                {
+                    return startPort;
+                }
+                startPort++;
+            }
+
+            return GetAvailablePort();
+        }
     }
 }