Mono support...trying to...

StackExchange.Redis/StackExchange/Redis/ConnectionMultiplexer.cs

@@ -194,13 +194,7 @@ internal void OnErrorMessage(EndPoint endpoint, string message)
         [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2202:Do not dispose objects multiple times")]
         private static void Write<T>(ZipArchive zip, string name, Task task, Action<T, StreamWriter> callback)
         {
-            var entry = zip.CreateEntry(name,
-#if __MonoCS__
-                CompressionLevel.Fastest
-#else
-                CompressionLevel.Optimal
-#endif
-                );
+            var entry = zip.CreateEntry(name, PlatformHelper.GetCompressionLevel(nameof(CompressionLevel.Optimal)));
             using (var stream = entry.Open())
             using (var writer = new StreamWriter(stream))
             {

StackExchange.Redis/StackExchange/Redis/PhysicalConnection.cs

@@ -741,9 +741,6 @@ SocketMode ISocketCallback.Connected(Stream stream, TextWriter log)
 
                     var ssl = new SslStream(stream, false, config.CertificateValidationCallback,
                         config.CertificateSelectionCallback ?? GetAmbientCertificateCallback()
-#if !__MonoCS__
-                        , EncryptionPolicy.RequireEncryption
-#endif
                         );
                     try
                     {

StackExchange.Redis/StackExchange/Redis/PlatformHelper.cs

+using System;
+using System.IO;
+using System.IO.Compression;
+using System.Net.Security;
+
+namespace StackExchange.Redis
+{
+    internal class PlatformHelper
+    {
+        public static SocketMode DefaultSocketMode = IsMono && IsUnix ? SocketMode.Async : SocketMode.Poll;
+
+        public static bool IsMono { get; } = Type.GetType("Mono.Runtime") != null;
+        public static bool IsUnix { get; } = (int)Environment.OSVersion.Platform == 4
+                                          || (int)Environment.OSVersion.Platform == 6
+                                          || (int)Environment.OSVersion.Platform == 128;
+
+        /// <summary>
+        /// Gets the compression level from a string, avoiding a naming bug inside ancient mono versions.
+        /// </summary>
+        /// <remarks>
+        /// See: https://github.com/mono/mono/commit/714efcf7d1f9c9017b370af16bb3117179dd60e5
+        /// </remarks>
+        /// <param name="level">The level.</param>
+        /// <returns></returns>
+        public static CompressionLevel GetCompressionLevel(string level)
+        {
+            try
+            {
+                return (CompressionLevel)Enum.Parse(typeof(CompressionLevel), level);
+            }
+            catch (ArgumentException)
+            {
+                // Oops, ancient mono here.. let's tray again.
+                return (CompressionLevel)Enum.Parse(typeof(CompressionLevel), level.Replace(nameof(CompressionLevel.Optimal), "Optional"));
+            }
+        }
+    }
+}

StackExchange.Redis/StackExchange/Redis/SocketManager.Poll.cs

@@ -10,7 +10,7 @@ namespace StackExchange.Redis
 {
     public partial class SocketManager
     {
-        internal const SocketMode DefaultSocketMode = SocketMode.Poll;
+        internal static SocketMode DefaultSocketMode = PlatformHelper.DefaultSocketMode;
         private static readonly IntPtr[] EmptyPointers = new IntPtr[0];
         private static readonly WaitCallback HelpProcessItems = state =>
         {
@@ -429,4 +429,4 @@ internal void Pulse()
         }
     }
 }
-#endif
+#endif
\ No newline at end of file