From 5532e736094f8d7bf17a991eda4a66f4b8fbbfc1 Mon Sep 17 00:00:00 2001
From: Pramod Valavala <prvalav@microsoft.com>
Date: Thu, 12 Aug 2021 11:42:18 +0530
Subject: [PATCH] Use next available port when default port is used

---
 .../Actions/HostActions/StartHostAction.cs    |  2 +-
 .../Helpers/NetworkHelpers.cs                 | 32 +++++++++++++++++++
 2 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/src/Azure.Functions.Cli/Actions/HostActions/StartHostAction.cs b/src/Azure.Functions.Cli/Actions/HostActions/StartHostAction.cs
index fb95d6f7b..e83f61770 100644
--- a/src/Azure.Functions.Cli/Actions/HostActions/StartHostAction.cs
+++ b/src/Azure.Functions.Cli/Actions/HostActions/StartHostAction.cs
@@ -82,7 +82,7 @@ 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
diff --git a/src/Azure.Functions.Cli/Helpers/NetworkHelpers.cs b/src/Azure.Functions.Cli/Helpers/NetworkHelpers.cs
index af0aec8c3..65abdce70 100644
--- a/src/Azure.Functions.Cli/Helpers/NetworkHelpers.cs
+++ b/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();
+        }
     }
 }
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