Attempt to reduce flake in BuggyBits sample app

profiler/src/Demos/Samples.BuggyBits/Program.cs

@@ -4,13 +4,13 @@
 // </copyright>
 using System;
 using System.Diagnostics;
-using System.Net;
-using System.Net.Sockets;
+using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
 using Datadog.Demos.Util;
 using Microsoft.AspNetCore.Hosting;
-using Microsoft.Extensions.Configuration;
+using Microsoft.AspNetCore.Hosting.Server;
+using Microsoft.AspNetCore.Hosting.Server.Features;
 using Microsoft.Extensions.Hosting;
 using Microsoft.Extensions.Logging;
 
@@ -56,36 +56,14 @@ public static async Task Main(string[] args)
 
             using (var host = CreateHostBuilder(args).Build())
             {
-                // ASP.NET Core accepts listening url via what is set by Visual Studio
-                // (from the launchsettings.json). It could be overriden by --Urls
-                // on the command line
-                var configuration = host.Services.GetService(typeof(IConfiguration)) as IConfiguration;
-                var rootUrl = configuration["urls"];
-
-                // otherwise, use the default ASP.NET Core value
-                if (string.IsNullOrEmpty(rootUrl))
-                {
-                    rootUrl = "http://localhost:5000";
-                }
-
-                // avoid race condition in CI to find an available port
-                int port = -1;
-                if (int.TryParse(rootUrl.Substring(rootUrl.LastIndexOf(':') + 1), out port))
-                {
-                    port = GetValidPort(port, 3);
-                    if (port != -1)
-                    {
-                        rootUrl = rootUrl.Substring(0, rootUrl.LastIndexOf(':') + 1) + port;
-                    }
-                }
+                await host.StartAsync();
 
+                var rootUrl = GetBoundRootUrl(host);
                 WriteLine($"Listening to {rootUrl}");
 
                 var cts = new CancellationTokenSource();
                 using (var selfInvoker = new SelfInvoker(cts.Token, scenario, nbIdleThreads, _disableLogs))
                 {
-                    await host.StartAsync();
-
                     WriteLine();
                     WriteLine($"Started at {DateTime.UtcNow}.");
 
@@ -161,62 +139,13 @@ public static IHostBuilder CreateHostBuilder(string[] args) =>
                     }
                 });
 
-        public static int GetOpenPort()
-        {
-            TcpListener tcpListener = null;
-            try
-            {
-                tcpListener = new TcpListener(IPAddress.Loopback, 0);
-                tcpListener.Start();
-                var port = ((IPEndPoint)tcpListener.LocalEndpoint).Port;
-                return port;
-            }
-            finally
-            {
-                tcpListener?.Stop();
-            }
-        }
-
-        private static int GetValidPort(int initialPort, int retries)
+        private static string GetBoundRootUrl(IHost host)
         {
-            var port = initialPort;
-            bool isPortValid = false;
-            while (true)
-            {
-                // seems like we can't reuse a listener if it fails to start,
-                // so create a new listener each time we retry
-                var listener = new HttpListener();
-                listener.Prefixes.Add($"http://127.0.0.1:{port}/");
-                listener.Prefixes.Add($"http://localhost:{port}/");
-
-                try
-                {
-                    listener.Start();
-
-                    // success
-                    isPortValid = true;
-                    break;
-                }
-                catch (HttpListenerException) when (retries > 0)
-                {
-                    // only catch the exception if there are retries left
-                    port = GetOpenPort();
-                    retries--;
-                }
-                finally
-                {
-                    listener.Close();
-                }
-            }
-
-            if (isPortValid)
-            {
-                return port;
-            }
-            else
-            {
-                return -1; // no valid port found
-            }
+            // Read the address Kestrel actually bound. Avoids race conditions where the caller
+            // passes a pre-picked port that another process grabs before we bind.
+            var server = (IServer)host.Services.GetService(typeof(IServer));
+            var address = server?.Features.Get<IServerAddressesFeature>()?.Addresses.FirstOrDefault();
+            return string.IsNullOrEmpty(address) ? "http://localhost:5000" : address.TrimEnd('/');
         }
 
         private static void ParseCommandLine(string[] args, out bool disableLogs, out TimeSpan timeout, out int iterations, out Scenario scenario, out int nbIdleThreads)

profiler/src/Demos/Samples.Website-AspNetCore01/Program.cs

@@ -5,11 +5,13 @@
 
 using System;
 using System.Diagnostics;
+using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
 using Datadog.Demos.Util;
 using Microsoft.AspNetCore.Hosting;
-using Microsoft.Extensions.Configuration;
+using Microsoft.AspNetCore.Hosting.Server;
+using Microsoft.AspNetCore.Hosting.Server.Features;
 using Microsoft.Extensions.Hosting;
 
 namespace Samples.Website_AspNetCore01
@@ -46,20 +48,6 @@ public static async Task Main(string[] args)
                 WriteLine($"host built in {sw.ElapsedMilliseconds} ms");
                 sw.Restart();
 
-                // ASP.NET Core accepts listening url via what is set by Visual Studio
-                // (from the launchsettings.json). It could be overriden by --Urls
-                // on the command line
-                var configuration = host.Services.GetService(typeof(IConfiguration)) as IConfiguration;
-                var rootUrl = configuration["Urls"];
-
-                // otherwise, use the default ASP.NET Core value
-                if (string.IsNullOrEmpty(rootUrl))
-                {
-                    rootUrl = "http://localhost:5000";
-                }
-
-                WriteLine($"Listening to {rootUrl}");
-
                 var cts = new CancellationTokenSource();
                 using (var selfInvoker = new SelfInvoker(cts.Token))
                 {
@@ -72,6 +60,12 @@ public static async Task Main(string[] args)
                     sw.Stop();
                     WriteLine($"host started in {sw.ElapsedMilliseconds} ms");
 
+                    // Read the address Kestrel actually bound (after StartAsync). Configuration["Urls"]
+                    // may be "http://127.0.0.1:0" when the test runner asks for a dynamic port, so the
+                    // bound address is the only reliable source of the real listening URL.
+                    var rootUrl = GetBoundRootUrl(host);
+                    WriteLine($"Listening to {rootUrl}");
+
                     WriteLine();
                     WriteLine($"Started at {DateTime.UtcNow}.");
 
@@ -107,6 +101,13 @@ public static IHostBuilder CreateHostBuilder(string[] args) =>
                     webBuilder.UseStartup<Startup>();
                 });
 
+        private static string GetBoundRootUrl(IHost host)
+        {
+            var server = (IServer)host.Services.GetService(typeof(IServer));
+            var address = server?.Features.Get<IServerAddressesFeature>()?.Addresses.FirstOrDefault();
+            return string.IsNullOrEmpty(address) ? "http://localhost:5000" : address.TrimEnd('/');
+        }
+
         // Helper method to output both to the console (when the app runs in the console)
         // and via Trace to see them while running under IISExpress both in Visual Studio
         // or with SysInternals DebugView (https://docs.microsoft.com/en-us/sysinternals/downloads/debugview)

profiler/test/Datadog.Profiler.IntegrationTests/Helpers/TestApplicationRunner.cs

@@ -7,6 +7,7 @@
 using System.Collections.Specialized;
 using System.Diagnostics;
 using System.IO;
+using System.Text.RegularExpressions;
 using Xunit;
 using Xunit.Abstractions;
 using Xunit.Sdk;
@@ -151,10 +152,11 @@ private string GetApplicationPath()
                 throw new Exception($"Unable to find executing assembly at {applicationPath}");
             }
 
-            // Look for a free open port to pass to the ASP.NET Core applications
-            // that accept --urls on their command line
-            _appListenerPort = $"http://localhost:{TcpPortProvider.GetOpenPort()}";
-            var arguments = $"--timeout {TestDurationInSeconds} --urls {_appListenerPort}";
+            // Use port 0 so Kestrel binds an OS-assigned free port and avoids the TOCTOU race
+            // of pre-picking a port. Bind to 127.0.0.1 explicitly: Kestrel rejects "localhost:0"
+            // with InvalidOperationException ("Dynamic port binding is not supported when binding
+            // to localhost"). The actual bound URL is parsed from stdout after the run.
+            var arguments = $"--timeout {TestDurationInSeconds} --urls http://127.0.0.1:0";
             if (!string.IsNullOrEmpty(_commandLine))
             {
                 arguments += $" {_commandLine}";
@@ -195,6 +197,7 @@ private void RunTest(MockDatadogAgent agent)
             var standardOutput = processHelper.StandardOutput;
             var errorOutput = processHelper.ErrorOutput;
             ProcessOutput = standardOutput;
+            _appListenerPort = ExtractListeningUrl(standardOutput);
 
             if (!ranToCompletion)
             {
@@ -251,5 +254,18 @@ private void SetEnvironmentVariables(StringDictionary environmentVariables, Mock
         {
             Environment.PopulateEnvironmentVariables(environmentVariables, agent, ProfilingExportsIntervalInSeconds, ServiceName);
         }
+
+        // Matches BuggyBits ("Listening to http://...") and ASP.NET Core's default Kestrel
+        // startup log ("Now listening on: http://..."). Returns null if neither is found.
+        private static string ExtractListeningUrl(string output)
+        {
+            if (string.IsNullOrEmpty(output))
+            {
+                return null;
+            }
+
+            var match = Regex.Match(output, @"(?:Listening to|Now listening on:)\s+(http://\S+)");
+            return match.Success ? match.Groups[1].Value.TrimEnd('/') : null;
+        }
     }
 }