Add port sharing support to Minimal benchmarks on Linux

Author: halter73

src/BenchmarksApps/TechEmpower/Minimal/Program.cs

@@ -5,6 +5,10 @@
 using Minimal;
 using Minimal.Database;
 using Minimal.Models;
+using Microsoft.AspNetCore.Server.Kestrel.Transport.Sockets;
+using System.Net.Sockets;
+using System.Net;
+using System.Runtime.InteropServices;
 
 var builder = WebApplication.CreateBuilder(args);
 
@@ -13,9 +17,41 @@
 
 builder.WebHost.ConfigureKestrel(options =>
 {
-     options.AllowSynchronousIO = true;
+    options.AllowSynchronousIO = true;
 });
 
+// Allow multiple processes bind to the same port. This also "works" on Windows in that it will
+// prevent address in use errors and hand off to another process if no others are available,
+// but it wouldn't round-robin new connections between processes like it will on Linux.
+if (RuntimeInformation.IsOSPlatform(OSPlatform.Linux))
+{
+    builder.WebHost.UseSockets(options =>
+    {
+        options.CreateBoundListenSocket = endpoint =>
+        {
+            if (endpoint is not IPEndPoint ip)
+            {
+                return SocketTransportOptions.CreateDefaultBoundListenSocket(endpoint);
+            }
+
+            // Normally, we'd call CreateDefaultBoundListenSocket for the IPEndpoint too, but we need
+            // to set ReuseAddress before calling bind, and CreateDefaultBoundListenSocket calls bind.
+            var listenSocket = new Socket(ip.AddressFamily, SocketType.Stream, ProtocolType.Tcp);
+
+            // Kestrel expects IPv6Any to bind to both IPv6 and IPv4
+            if (ip.Address.Equals(IPAddress.IPv6Any))
+            {
+                listenSocket.DualMode = true;
+            }
+
+            listenSocket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReuseAddress, true);
+            listenSocket.Bind(ip);
+
+            return listenSocket;
+        };
+    });
+}
+
 // Load custom configuration
 var appSettings = new AppSettings();
 builder.Configuration.Bind(appSettings);
@@ -40,7 +76,8 @@
 var createFortunesTemplate = RazorSlice.ResolveSliceFactory<List<Fortune>>("/Templates/Fortunes.cshtml");
 var htmlEncoder = CreateHtmlEncoder();
 
-app.MapGet("/fortunes", async (HttpContext context, Db db) => {
+app.MapGet("/fortunes", async (HttpContext context, Db db) =>
+{
     var fortunes = await db.LoadFortunesRows();
     var template = (RazorSliceHttpResult<List<Fortune>>)createFortunesTemplate(fortunes);
     template.HtmlEncoder = htmlEncoder;