non-connected fix for subscriber

Author: mgravell

src/StackExchange.Redis/MultiGroupDatabase.Async.cs

@@ -11,7 +11,7 @@ public Task<RedisValue> DebugObjectAsync(RedisKey key, CommandFlags flags = Comm
         => GetActiveDatabase().DebugObjectAsync(key, flags);
 
     public Task<EndPoint?> IdentifyEndpointAsync(RedisKey key = default, CommandFlags flags = CommandFlags.None)
-        => TryGetActiveDatabase()?.IdentifyEndpointAsync(key, flags) ?? NoEndpoint;
+        => TryGetActiveDatabase()?.IdentifyEndpointAsync(key, flags) ?? MultiGroupMultiplexer.NoEndpoint;
 
     public Task KeyMigrateAsync(RedisKey key, EndPoint toServer, int toDatabase = 0, int timeoutMilliseconds = 0, MigrateOptions migrateOptions = MigrateOptions.None, CommandFlags flags = CommandFlags.None)
         => GetActiveDatabase().KeyMigrateAsync(key, toServer, toDatabase, timeoutMilliseconds, migrateOptions, flags);

src/StackExchange.Redis/MultiGroupDatabase.cs

@@ -17,10 +17,6 @@ internal sealed partial class MultiGroupDatabase(MultiGroupMultiplexer parent, i
     // member, for use by members that have an obvious trivial result when disconnected
     private IDatabase? TryGetActiveDatabase() => parent.TryGetActive()?.GetDatabase(database, asyncState);
 
-    // a completed "no endpoint" result, reused for IdentifyEndpointAsync when the group is fully down
-    internal static readonly System.Threading.Tasks.Task<System.Net.EndPoint?> NoEndpoint
-        = System.Threading.Tasks.Task.FromResult<System.Net.EndPoint?>(null);
-
     // Core methods
     public IBatch CreateBatch(object? asyncState = null)
         => GetActiveDatabase().CreateBatch(asyncState);

src/StackExchange.Redis/MultiGroupMultiplexer.cs

@@ -258,6 +258,9 @@ static ConnectionMultiplexer Throw() =>
     // non-throwing twin of Active, for callers that have a trivial answer when the group is fully down
     internal ConnectionMultiplexer? TryGetActive() => _active;
 
+    // a completed "no endpoint" result, shared by the database/subscriber facades when the group is fully down
+    internal static readonly Task<EndPoint?> NoEndpoint = Task.FromResult<EndPoint?>(null);
+
     private ConnectionGroupMember? GetActiveMember()
     {
         var active = _active;

src/StackExchange.Redis/MultiGroupSubscriber.cs

@@ -9,6 +9,10 @@ internal sealed partial class MultiGroupSubscriber(MultiGroupMultiplexer parent,
     // for a lot of things, we can defer through to the active implementation
     private ISubscriber GetActiveSubscriber() => parent.Active.GetSubscriber(asyncState);
 
+    // non-throwing twin of GetActiveSubscriber: returns null when the group currently has no active
+    // member, for use by members that have an obvious trivial result when disconnected
+    private ISubscriber? TryGetActiveSubscriber() => parent.TryGetActive()?.GetSubscriber(asyncState);
+
     public IConnectionMultiplexer Multiplexer => parent;
 
     public bool TryWait(Task task) => GetActiveSubscriber().TryWait(task);
@@ -24,18 +28,18 @@ internal sealed partial class MultiGroupSubscriber(MultiGroupMultiplexer parent,
     public Task<TimeSpan> PingAsync(CommandFlags flags = CommandFlags.None) => GetActiveSubscriber().PingAsync(flags);
 
     public EndPoint? IdentifyEndpoint(RedisChannel channel, CommandFlags flags = CommandFlags.None) =>
-        GetActiveSubscriber().IdentifyEndpoint(channel, flags);
+        TryGetActiveSubscriber()?.IdentifyEndpoint(channel, flags);
 
     public Task<EndPoint?> IdentifyEndpointAsync(RedisChannel channel, CommandFlags flags = CommandFlags.None) =>
-        GetActiveSubscriber().IdentifyEndpointAsync(channel, flags);
+        TryGetActiveSubscriber()?.IdentifyEndpointAsync(channel, flags) ?? MultiGroupMultiplexer.NoEndpoint;
 
-    public bool IsConnected(RedisChannel channel = default) => GetActiveSubscriber().IsConnected();
+    public bool IsConnected(RedisChannel channel = default) => TryGetActiveSubscriber()?.IsConnected() ?? false;
 
     public long Publish(RedisChannel channel, RedisValue message, CommandFlags flags = CommandFlags.None)
         => GetActiveSubscriber().Publish(channel, message, flags);
 
     public Task<long> PublishAsync(RedisChannel channel, RedisValue message, CommandFlags flags = CommandFlags.None)
         => GetActiveSubscriber().PublishAsync(channel, message, flags);
 
-    public EndPoint? SubscribedEndpoint(RedisChannel channel) => GetActiveSubscriber().SubscribedEndpoint(channel);
+    public EndPoint? SubscribedEndpoint(RedisChannel channel) => TryGetActiveSubscriber()?.SubscribedEndpoint(channel);
 }