Fix #356: Fix exceptions thrown by Drain

src/NATS.Client/Conn.cs

@@ -3890,6 +3890,13 @@ private void drain(int timeout)
 
             lock (mu)
             {
+                if (isClosed())
+                    throw new NATSConnectionClosedException();
+
+                // if we're already draining, exit.
+                if (isDrainingSubs() || isDrainingPubs())
+                    return;
+
                 lsubs = subs.Values;
                 status = ConnState.DRAINING_SUBS;
             }
@@ -3974,11 +3981,6 @@ public void Drain(int timeout)
             if (timeout <= 0)
                 throw new ArgumentOutOfRangeException(nameof(timeout), "Timeout must be greater than zero.");
 
-            lock (mu)
-            {
-                status = ConnState.DRAINING_SUBS;
-            }
-
             drain(timeout);
         }
 
@@ -4019,11 +4021,6 @@ public Task DrainAsync(int timeout)
             if (timeout <= 0)
                 throw new ArgumentOutOfRangeException(nameof(timeout), "Timeout must be greater than zero.");
 
-            lock (mu)
-            {
-                status = ConnState.DRAINING_SUBS;
-            }
-
             return Task.Run(() => drain(timeout));
         }
 

src/Tests/IntegrationTests/TestConnection.cs

@@ -1093,6 +1093,7 @@ public async Task TestDrainStateBehavior()
                 {
                     closed.Set();
                 };
+
                 using (var c = Context.ConnectionFactory.CreateConnection(opts))
                 {
                     using (c.SubscribeAsync("foo", (obj, args) =>
@@ -1109,6 +1110,8 @@ public async Task TestDrainStateBehavior()
                         // give us a long timeout to run our test.
                         var drainTask = c.DrainAsync(10000);
 
+                        // Sleep a bit to ensure the drain task is running.
+                        Thread.Sleep(100);
                         Assert.True(c.State == ConnState.DRAINING_SUBS);
                         Assert.True(c.IsDraining());
 
@@ -1124,6 +1127,12 @@ public async Task TestDrainStateBehavior()
                         Assert.True(closed.WaitOne(10000));
                     }
                 }
+
+                // Now test connection state checking in drain after being closed via API.
+                var conn = Context.ConnectionFactory.CreateConnection(opts);
+                conn.Close();
+                _ = Assert.Throws<NATSConnectionClosedException>(() => conn.Drain());
+                await Assert.ThrowsAsync<NATSConnectionClosedException>(() => { return conn.DrainAsync(); });
             }
         }