Improved robustness of TCP connection handling + test

Capnp.Net.Runtime.Tests/TcpRpcInterop.cs

@@ -36,7 +36,7 @@ namespace Capnp.Net.Runtime.Tests
 
         Process _currentProcess;
 
-        void LaunchCompatTestProcess(string whichTest, Action<StreamReader> test)
+        bool TryLaunchCompatTestProcess(string whichTest, Action<StreamReader> test)
         {
             string myPath = Path.GetDirectoryName(typeof(TcpRpcInterop).Assembly.Location);
             string config;
@@ -71,6 +71,12 @@ namespace Capnp.Net.Runtime.Tests
                         "Problem after launching test process");
 
                     test(_currentProcess.StandardOutput);
+
+                    return true;
+                }
+                catch (AssertFailedException)
+                {
+                    return false;
                 }
                 finally
                 {
@@ -85,6 +91,20 @@ namespace Capnp.Net.Runtime.Tests
             }
         }
 
+        void LaunchCompatTestProcess(string whichTest, Action<StreamReader> test)
+        {
+            for (int retry = 0; retry < 5; retry++)
+            {
+                if (TryLaunchCompatTestProcess(whichTest, test))
+                    return;
+
+                if (whichTest.StartsWith("server:"))
+                    PrepareNextTest();
+            }
+
+            Assert.Fail("Problem after launching test process");
+        }
+
         void SendInput(string line)
         {
             _currentProcess.StandardInput.WriteLine(line);

Capnp.Net.Runtime.Tests/TestBase.cs

@@ -5,6 +5,7 @@ using System;
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Net;
+using System.Net.Sockets;
 using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
@@ -21,7 +22,29 @@ namespace Capnp.Net.Runtime.Tests
         protected ILogger Logger { get; set; }
 
         protected TcpRpcClient SetupClient() => new TcpRpcClient("localhost", TcpPort);
-        protected TcpRpcServer SetupServer() => new TcpRpcServer(IPAddress.Any, TcpPort);
+        protected TcpRpcServer SetupServer()
+        {
+            int attempt = 0;
+
+            while (true)
+            {
+                try
+                {
+                    return new TcpRpcServer(IPAddress.Any, TcpPort);
+                }
+                catch (SocketException)
+                {
+                    // If the TCP listening port is occupied by some other process, 
+                    // retry with a different one
+
+                    if (attempt == 5)
+                        throw;
+                }
+
+                IncrementTcpPort();
+                ++attempt;
+            }
+        }
 
         protected (TcpRpcServer, TcpRpcClient) SetupClientServerPair()
         {

Capnp.Net.Runtime/Rpc/TcpRpcServer.cs

@@ -284,7 +284,9 @@ namespace Capnp.Rpc
             _listener = new TcpListener(localAddr, port);
             _listener.ExclusiveAddressUse = false;
 
-            for (int retry = 0; retry < 5; retry++)
+            int attempt = 0;
+
+            while (true)
             {
                 try
                 {
@@ -293,9 +295,13 @@ namespace Capnp.Rpc
                 }
                 catch (SocketException socketException)
                 {
-                    Logger.LogWarning($"Failed to listen on port {port}, attempt {retry}: {socketException}");
-                    Thread.Sleep(10);
+                    if (attempt == 5)
+                        throw;
+                    
+                    Logger.LogWarning($"Failed to listen on port {port}, attempt {attempt}: {socketException}");
                 }
+
+                ++attempt;
             }
 
             _acceptorThread = new Thread(AcceptClients);