Validate hostname in SocketFrameHandler to restore expectation that an exception will be thrown. Ugh.

Author: lukebakken

projects/RabbitMQ.Client/client/api/DefaultEndpointResolver.cs

@@ -37,8 +37,10 @@ namespace RabbitMQ.Client
 {
     public class DefaultEndpointResolver : IEndpointResolver
     {
+#if !NET6_0_OR_GREATER
+        private static readonly Random s_rnd = new Random();
+#endif
         private readonly List<AmqpTcpEndpoint> _endpoints;
-        private readonly Random _rnd = new Random();
 
         public DefaultEndpointResolver(IEnumerable<AmqpTcpEndpoint> tcpEndpoints)
         {
@@ -50,7 +52,7 @@ public IEnumerable<AmqpTcpEndpoint> All()
 #if NET6_0_OR_GREATER
             return _endpoints.OrderBy(item => Random.Shared.Next());
 #else
-            return _endpoints.OrderBy(item => _rnd.Next());
+            return _endpoints.OrderBy(item => s_rnd.Next());
 #endif
         }
     }

projects/RabbitMQ.Client/client/impl/SocketFrameHandler.cs

@@ -45,6 +45,7 @@ namespace RabbitMQ.Client.Impl
     internal sealed class SocketFrameHandler : IFrameHandler
     {
         private readonly AmqpTcpEndpoint _amqpTcpEndpoint;
+        private readonly IPAddress[] _amqpTcpEndpointAddresses;
         private readonly Func<AddressFamily, ITcpClient> _socketFactory;
         private readonly TimeSpan _connectionTimeout;
 
@@ -74,6 +75,15 @@ public SocketFrameHandler(AmqpTcpEndpoint amqpTcpEndpoint,
             _readTimeout = readTimeout;
             _writeTimeout = writeTimeout;
 
+            /*
+             * Resolve the hostname early to validate.
+             * Used by SelectOne in EndpointResolverExtensions, which catches the thrown exception
+             * if the hostname does not resolve. It's set up this way so that CreateFrameHandler captures
+             * various configuration values when selecting a SocketFrameHandler for the Connection to use.
+             * TODO this is not ideal, because it does not allow using Dns.GetHostAddressesAsync
+             */
+            _amqpTcpEndpointAddresses = Dns.GetHostAddresses(_amqpTcpEndpoint.HostName);
+
             var channel = Channel.CreateBounded<RentedMemory>(
                 new BoundedChannelOptions(128)
                 {
@@ -138,11 +148,8 @@ public TimeSpan WriteTimeout
 
         public async Task ConnectAsync(CancellationToken cancellationToken)
         {
-            // Resolve the hostname to know if it's even possible to even try IPv6
             // TODO cancellation token
-            IPAddress[] adds = await Dns.GetHostAddressesAsync(_amqpTcpEndpoint.HostName)
-                .ConfigureAwait(false);
-            IPAddress ipv6 = TcpClientAdapter.GetMatchingHost(adds, AddressFamily.InterNetworkV6);
+            IPAddress ipv6 = TcpClientAdapter.GetMatchingHost(_amqpTcpEndpointAddresses, AddressFamily.InterNetworkV6);
 
             if (ipv6 == default(IPAddress))
             {
@@ -168,7 +175,7 @@ public async Task ConnectAsync(CancellationToken cancellationToken)
 
             if (_socket is null)
             {
-                IPAddress ipv4 = TcpClientAdapter.GetMatchingHost(adds, AddressFamily.InterNetwork);
+                IPAddress ipv4 = TcpClientAdapter.GetMatchingHost(_amqpTcpEndpointAddresses, AddressFamily.InterNetwork);
                 if (ipv4 == default(IPAddress))
                 {
                     throw new ConnectFailureException("Connection failed", new ArgumentException($"No ip address could be resolved for {_amqpTcpEndpoint.HostName}"));