Proxy: move to extension methods (#1982)

This should make PRs like #1977 and #1425 much easier.

src/StackExchange.Redis/ConnectionMultiplexer.cs

@@ -572,7 +572,7 @@ private static void WriteNormalizingLineEndings(string source, StreamWriter writ
 
         /// <summary>
         /// Raised when nodes are explicitly requested to reconfigure via broadcast.
-        /// This usually means primary/replica role changes.
+        /// This usually means primary/replica changes.
         /// </summary>
         public event EventHandler<EndPointEventArgs> ConfigurationChangedBroadcast;
 
@@ -1421,7 +1421,10 @@ internal long LastHeartbeatSecondsAgo
         /// <param name="asyncState">The async state object to pass to the created <see cref="RedisSubscriber"/>.</param>
         public ISubscriber GetSubscriber(object asyncState = null)
         {
-            if (RawConfig.Proxy == Proxy.Twemproxy) throw new NotSupportedException("The pub/sub API is not available via twemproxy");
+            if (!RawConfig.Proxy.SupportsPubSub())
+            {
+                throw new NotSupportedException($"The pub/sub API is not available via {RawConfig.Proxy}");
+            }
             return new RedisSubscriber(this, asyncState);
         }
 
@@ -1439,9 +1442,9 @@ internal int ApplyDefaultDatabase(int db)
                 throw new ArgumentOutOfRangeException(nameof(db));
             }
 
-            if (db != 0 && RawConfig.Proxy == Proxy.Twemproxy)
+            if (db != 0 && !RawConfig.Proxy.SupportsDatabases())
             {
-                throw new NotSupportedException("twemproxy only supports database 0");
+                throw new NotSupportedException($"{RawConfig.Proxy} only supports database 0");
             }
 
             return db;
@@ -1509,7 +1512,10 @@ public IDatabase GetDatabase(int db = -1, object asyncState = null)
         public IServer GetServer(EndPoint endpoint, object asyncState = null)
         {
             if (endpoint == null) throw new ArgumentNullException(nameof(endpoint));
-            if (RawConfig.Proxy == Proxy.Twemproxy) throw new NotSupportedException("The server API is not available via twemproxy");
+            if (!RawConfig.Proxy.SupportsServerApi())
+            {
+                throw new NotSupportedException($"The server API is not available via {RawConfig.Proxy}");
+            }
             var server = (ServerEndPoint)servers[endpoint];
             if (server == null) throw new ArgumentException("The specified endpoint is not defined", nameof(endpoint));
             return new RedisServer(this, server, asyncState);
@@ -1885,18 +1891,24 @@ internal async Task<bool> ReconfigureAsync(bool first, bool reconfigureAll, LogP
                             ServerSelectionStrategy.ServerType = ServerType.Standalone;
                         }
 
-                        var preferred = NominatePreferredMaster(log, servers, useTieBreakers, masters);
-                        foreach (var master in masters)
+                        // If multiple primaries are detected, nominate the preferred one
+                        // ...but not if the type of server we're connected to supports and expects multiple primaries
+                        // ...for those cases, we want to allow sending to any primary endpoint.
+                        if (ServerSelectionStrategy.ServerType.HasSinglePrimary())
                         {
-                            if (master == preferred || master.IsReplica)
-                            {
-                                log?.WriteLine($"{Format.ToString(master)}: Clearing as RedundantMaster");
-                                master.ClearUnselectable(UnselectableFlags.RedundantMaster);
-                            }
-                            else
+                            var preferred = NominatePreferredMaster(log, servers, useTieBreakers, masters);
+                            foreach (var master in masters)
                             {
-                                log?.WriteLine($"{Format.ToString(master)}: Setting as RedundantMaster");
-                                master.SetUnselectable(UnselectableFlags.RedundantMaster);
+                                if (master == preferred || master.IsReplica)
+                                {
+                                    log?.WriteLine($"{Format.ToString(master)}: Clearing as RedundantMaster");
+                                    master.ClearUnselectable(UnselectableFlags.RedundantMaster);
+                                }
+                                else
+                                {
+                                    log?.WriteLine($"{Format.ToString(master)}: Setting as RedundantMaster");
+                                    master.SetUnselectable(UnselectableFlags.RedundantMaster);
+                                }
                             }
                         }
                     }

src/StackExchange.Redis/Enums/Proxy.cs

@@ -14,4 +14,34 @@ public enum Proxy
         /// </summary>
         Twemproxy,
     }
+
+    internal static class ProxyExtensions
+    {
+        /// <summary>
+        /// Whether a proxy supports databases (e.g. database > 0).
+        /// </summary>
+        public static bool SupportsDatabases(this Proxy proxy) => proxy switch
+        {
+            Proxy.Twemproxy => false,
+            _ => true
+        };
+
+        /// <summary>
+        /// Whether a proxy supports pub/sub.
+        /// </summary>
+        public static bool SupportsPubSub(this Proxy proxy) => proxy switch
+        {
+            Proxy.Twemproxy => false,
+            _ => true
+        };
+
+        /// <summary>
+        /// Whether a proxy supports the <c>ConnectionMultiplexer.GetServer</c>.
+        /// </summary>
+        public static bool SupportsServerApi(this Proxy proxy) => proxy switch
+        {
+            Proxy.Twemproxy => false,
+            _ => true
+        };
+    }
 }

src/StackExchange.Redis/Enums/ServerType.cs

@@ -22,4 +22,24 @@ public enum ServerType
         /// </summary>
         Twemproxy,
     }
+
+    internal static class ServerTypeExtensions
+    {
+        /// <summary>
+        /// Whether a server type can have only a single primary, meaning an election if multiple are found.
+        /// </summary>
+        public static bool HasSinglePrimary(this ServerType type) => type switch
+        {
+            _ => true
+        };
+
+        /// <summary>
+        /// Whether a server type supports <see cref="ServerEndPoint.AutoConfigureAsync(PhysicalConnection, ConnectionMultiplexer.LogProxy)"/>.
+        /// </summary>
+        public static bool SupportsAutoConfigure(this ServerType type) => type switch
+        {
+            ServerType.Twemproxy => false,
+            _ => true
+        };
+    }
 }

src/StackExchange.Redis/Interfaces/IConnectionMultiplexer.cs

@@ -107,7 +107,7 @@ public interface IConnectionMultiplexer : IDisposable
 
         /// <summary>
         /// Raised when nodes are explicitly requested to reconfigure via broadcast.
-        /// This usually means primary/replica role changes.
+        /// This usually means primary/replica changes.
         /// </summary>
         event EventHandler<EndPointEventArgs> ConfigurationChangedBroadcast;
 

src/StackExchange.Redis/ServerEndPoint.cs

@@ -328,10 +328,10 @@ internal void AddScript(string script, byte[] hash)
 
         internal async Task AutoConfigureAsync(PhysicalConnection connection, LogProxy log = null)
         {
-            if (serverType == ServerType.Twemproxy)
+            if (!serverType.SupportsAutoConfigure())
             {
-                // don't try to detect configuration; all the config commands are disabled, and
-                // the fallback master/replica detection won't help
+                // Don't try to detect configuration.
+                // All the config commands are disabled and the fallback primary/replica detection won't help
                 return;
             }