Improve exception messages 2

Author: MihaZupan

src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/SocksException.cs

@@ -7,8 +7,8 @@ namespace System.Net.Http
 {
     internal class SocksException : IOException
     {
-        public SocksException(string message) : base(message)
-        {
-        }
+        public SocksException(string message) : base(message) { }
+
+        public SocksException(string message, Exception innerException) : base(message, innerException) { }
     }
 }

src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/SocksHelper.cs

@@ -227,7 +227,7 @@ private static async ValueTask EstablishSocks4TunnelAsync(Stream stream, bool is
                 BinaryPrimitives.WriteUInt16BigEndian(buffer.AsSpan(2), (ushort)port);
 
                 IPAddress? ipv4Address = null;
-                if (IPAddress.TryParse(host, out var hostIP))
+                if (IPAddress.TryParse(host, out IPAddress? hostIP))
                 {
                     if (hostIP.AddressFamily == AddressFamily.InterNetwork)
                     {
@@ -245,9 +245,17 @@ private static async ValueTask EstablishSocks4TunnelAsync(Stream stream, bool is
                 else if (!isVersion4a)
                 {
                     // Socks4 does not support domain names - try to resolve it here
-                    var addresses = async
-                        ? await Dns.GetHostAddressesAsync(host, AddressFamily.InterNetwork, cancellationToken).ConfigureAwait(false)
-                        : Dns.GetHostAddresses(host, AddressFamily.InterNetwork);
+                    IPAddress[] addresses;
+                    try
+                    {
+                        addresses = async
+                            ? await Dns.GetHostAddressesAsync(host, AddressFamily.InterNetwork, cancellationToken).ConfigureAwait(false)
+                            : Dns.GetHostAddresses(host, AddressFamily.InterNetwork);
+                    }
+                    catch (Exception ex)
+                    {
+                        throw new SocksException(SR.net_socks_no_ipv4_address, ex);
+                    }
 
                     if (addresses.Length == 0)
                     {

src/libraries/System.Net.Http/tests/FunctionalTests/Socks/SocksProxyTest.cs

@@ -76,6 +76,8 @@ public static IEnumerable<object[]> TestExceptionalAsync_MemberData()
                 yield return new object[] { scheme, "localhost", true, new NetworkCredential(new string('a', 256), "foo"), "Encoding the UserName took more than the maximum of 255 bytes." };
             }
 
+            yield return new object[] { "socks4", new string('a', 256), false, null, "Failed to resolve the destination host to an IPv4 address." };
+
             foreach (string scheme in new[] { "socks4a", "socks5" })
             {
                 yield return new object[] { scheme, new string('a', 256), false, null, "Encoding the host took more than the maximum of 255 bytes." };