Increase consume and fetch channel size (#246)

Increase consume and fetch channel size to avoid blocking the socket reads
for other operations. I think we have done this change before but somehow
reverted back during merges perhaps.

src/NATS.Client.JetStream/Internal/NatsJSConsume.cs

@@ -130,13 +130,11 @@ public NatsJSConsume(
             Timeout.Infinite,
             Timeout.Infinite);
 
-        // Keep user channel small to avoid blocking the user code
-        // when disposed otherwise channel reader will continue delivering messages
-        // if there are messages queued up already. This channel is used to pass messages
+        // This channel is used to pass messages
         // to the user from the subscription channel (which should be set to a
         // sufficiently large value to avoid blocking socket reads in the
         // NATS connection).
-        _userMsgs = Channel.CreateBounded<NatsJSMsg<TMsg>>(1);
+        _userMsgs = Channel.CreateBounded<NatsJSMsg<TMsg>>(1000);
         Msgs = _userMsgs.Reader;
 
         // Capacity as 1 is enough here since it's used for signaling only.

src/NATS.Client.JetStream/Internal/NatsJSFetch.cs

@@ -67,10 +67,11 @@ public NatsJSFetch(
         _pendingMsgs = _maxMsgs;
         _pendingBytes = _maxBytes;
 
-        // Keep user channel small to avoid blocking the user code when disposed,
-        // otherwise channel reader will continue delivering messages even after
-        // this 'fetch' object being disposed.
-        _userMsgs = Channel.CreateBounded<NatsJSMsg<TMsg>>(1);
+        // This channel is used to pass messages
+        // to the user from the subscription channel (which should be set to a
+        // sufficiently large value to avoid blocking socket reads in the
+        // NATS connection).
+        _userMsgs = Channel.CreateBounded<NatsJSMsg<TMsg>>(1000);
         Msgs = _userMsgs.Reader;
 
         if (_debug)

tests/NATS.Client.JetStream.Tests/DoubleAckTest.cs

@@ -0,0 +1,67 @@
+using NATS.Client.Core.Tests;
+
+namespace NATS.Client.JetStream.Tests;
+
+public class DoubleAckTest
+{
+    [Fact]
+    public async Task Fetch_should_not_block_socket()
+    {
+        var cts = new CancellationTokenSource(TimeSpan.FromSeconds(30));
+        await using var server = NatsServer.StartJS();
+
+        await using var nats = server.CreateClientConnection();
+
+        var js = new NatsJSContext(nats);
+        await js.CreateStreamAsync("s1", new[] { "s1.*" }, cts.Token);
+
+        for (var i = 0; i < 100; i++)
+        {
+            var ack = await js.PublishAsync("s1.foo", i, cancellationToken: cts.Token);
+            ack.EnsureSuccess();
+        }
+
+        // fetch loop
+        {
+            var consumer = (NatsJSConsumer) await js.CreateConsumerAsync("s1", "c1", cancellationToken: cts.Token);
+
+            var fetchOpts = new NatsJSFetchOpts
+            {
+                MaxMsgs = 100, Expires = TimeSpan.FromSeconds(5),
+            };
+
+            var count = 0;
+            await foreach (var msg in consumer.FetchAsync<int>(opts: fetchOpts, cancellationToken: cts.Token))
+            {
+                // double ack will use the same TCP stream to wait for the ACK from the server
+                // fetch must not block the socket so that the ACK can be received
+                await msg.AckAsync(new AckOpts(DoubleAck: true), cts.Token);
+                count++;
+            }
+
+            Assert.Equal(100, count);
+        }
+
+        // consume loop
+        {
+            var consumer = (NatsJSConsumer) await js.CreateConsumerAsync("s1", "c2", cancellationToken: cts.Token);
+
+            var opts = new NatsJSConsumeOpts
+            {
+                MaxMsgs = 100, Expires = TimeSpan.FromSeconds(5),
+            };
+
+            var count = 0;
+            await foreach (var msg in consumer.ConsumeAsync<int>(opts: opts, cancellationToken: cts.Token))
+            {
+                // double ack will use the same TCP stream to wait for the ACK from the server
+                // fetch must not block the socket so that the ACK can be received
+                await msg.AckAsync(new AckOpts(DoubleAck: true), cts.Token);
+                count++;
+            }
+
+            Assert.Equal(100, count);
+        }
+
+    }
+}