expose IAsyncEnumerable on ChannelMessageQueue

fix #2400

Author: mgravell

docs/ReleaseNotes.md

@@ -8,11 +8,11 @@ Current package versions:
 
 ## Unreleased
 
-No pending changes.
+- Fix [#2400](https://github.com/StackExchange/StackExchange.Redis/issues/2400): Expose `ChannelMessageQueue` as `IAsyncEnumerable<ChannelMessage>` ([#???? by mgravell](https://github.com/StackExchange/StackExchange.Redis/pull/????))
 
 ## 2.6.96
 
-- Fix [#2350](https://github.com/StackExchange/StackExchange.Redis/issues/2350): Properly parse lua script paramters in all cultures ([#2351 by NickCraver](https://github.com/StackExchange/StackExchange.Redis/pull/2351))
+- Fix [#2350](https://github.com/StackExchange/StackExchange.Redis/issues/2350): Properly parse lua script parameters in all cultures ([#2351 by NickCraver](https://github.com/StackExchange/StackExchange.Redis/pull/2351))
 - Fix [#2362](https://github.com/StackExchange/StackExchange.Redis/issues/2362): Set `RedisConnectionException.FailureType` to `AuthenticationFailure` on all authentication scenarios for better handling ([#2367 by NickCraver](https://github.com/StackExchange/StackExchange.Redis/pull/2367))
 - Fix [#2368](https://github.com/StackExchange/StackExchange.Redis/issues/2368): Support `RedisValue.Length()` for all storage types ([#2370 by mgravell](https://github.com/StackExchange/StackExchange.Redis/pull/2370))
 - Fix [#2376](https://github.com/StackExchange/StackExchange.Redis/issues/2376): Avoid a (rare) deadlock scenario ([#2378 by mgravell](https://github.com/StackExchange/StackExchange.Redis/pull/2378))

src/StackExchange.Redis/ChannelMessageQueue.cs

@@ -1,5 +1,7 @@
 using System;
+using System.Collections.Generic;
 using System.Reflection;
+using System.Runtime.CompilerServices;
 using System.Threading;
 using System.Threading.Channels;
 using System.Threading.Tasks;
@@ -66,7 +68,7 @@ internal ChannelMessage(ChannelMessageQueue queue, in RedisChannel channel, in R
     /// To create a ChannelMessageQueue, use <see cref="ISubscriber.Subscribe(RedisChannel, CommandFlags)"/>
     /// or <see cref="ISubscriber.SubscribeAsync(RedisChannel, CommandFlags)"/>.
     /// </remarks>
-    public sealed class ChannelMessageQueue
+    public sealed class ChannelMessageQueue : IAsyncEnumerable<ChannelMessage>
     {
         private readonly Channel<ChannelMessage> _queue;
         /// <summary>
@@ -319,10 +321,7 @@ internal void UnsubscribeImpl(Exception? error = null, CommandFlags flags = Comm
         {
             var parent = _parent;
             _parent = null;
-            if (parent != null)
-            {
-                parent.UnsubscribeAsync(Channel, null, this, flags);
-            }
+            parent?.UnsubscribeAsync(Channel, null, this, flags);
             _queue.Writer.TryComplete(error);
         }
 
@@ -348,5 +347,22 @@ internal async Task UnsubscribeAsyncImpl(Exception? error = null, CommandFlags f
         /// </summary>
         /// <param name="flags">The flags to use when unsubscribing.</param>
         public Task UnsubscribeAsync(CommandFlags flags = CommandFlags.None) => UnsubscribeAsyncImpl(null, flags);
+
+        /// <inheritdoc cref="IAsyncEnumerable{ChannelMessage}.GetAsyncEnumerator(CancellationToken)"/>
+#if NETCOREAPP3_0_OR_GREATER
+        public IAsyncEnumerator<ChannelMessage> GetAsyncEnumerator(CancellationToken cancellationToken = default)
+            => _queue.Reader.ReadAllAsync().GetAsyncEnumerator(cancellationToken);
+#else
+        public async IAsyncEnumerator<ChannelMessage> GetAsyncEnumerator(CancellationToken cancellationToken = default)
+        {
+            while (await _queue.Reader.WaitToReadAsync(cancellationToken).ConfigureAwait(false))
+            {
+                while (_queue.Reader.TryRead(out var item))
+                {
+                    yield return item;
+                }
+            }
+        }
+#endif
     }
 }

src/StackExchange.Redis/PublicAPI/PublicAPI.Unshipped.txt

@@ -1 +1 @@
-
+StackExchange.Redis.ChannelMessageQueue.GetAsyncEnumerator(System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) -> System.Collections.Generic.IAsyncEnumerator<StackExchange.Redis.ChannelMessage>!

tests/StackExchange.Redis.Tests/PubSubTests.cs

@@ -308,6 +308,40 @@ private void TestMassivePublish(ISubscriber sub, string channel, string caption)
         Assert.True(withFAF.ElapsedMilliseconds < withAsync.ElapsedMilliseconds + 3000, caption);
     }
 
+    [Fact]
+    public async Task SubscribeAsyncEnumerable()
+    {
+        using var conn = Create(syncTimeout: 20000, shared: false, log: Writer);
+
+        var sub = conn.GetSubscriber();
+        RedisChannel channel = Me();
+
+        const int TO_SEND = 5;
+        var gotall = new TaskCompletionSource<int>();
+
+        var source = await sub.SubscribeAsync(channel);
+        var op = Task.Run(async () => {
+            int count = 0;
+            await foreach (var item in source)
+            {
+                count++;
+                if (count == TO_SEND) gotall.TrySetResult(count);
+            }
+            return count;
+        });
+
+        for (int i = 0; i < TO_SEND; i++)
+        {
+            await sub.PublishAsync(channel, i);
+        }
+        await gotall.Task.WithTimeout(5000);
+
+        // check the enumerator exits cleanly
+        sub.Unsubscribe(channel);
+        var count = await op.WithTimeout(1000);
+        Assert.Equal(5, count);
+    }
+
     [Fact]
     public async Task PubSubGetAllAnyOrder()
     {