SmtpStream.QueueCommand goes to endless loop in TryQueueCommand

[alexander-kucherov]

Describe the bug
SmtpStream.QueueCommand goes to endless loop in TryQueueCommand if command length is greater than output buffer size (4096).
It was broken by commit
In my case needed bytes always greater than 4096 and it always return false. Callsite has while loop

			while (!TryQueueCommand (encoder, command, ref index))
				Flush (cancellationToken);

In this case it's endless.

Platform (please complete the following information):

• OS: Windows
• .NET Runtime: net7.0
• MailKit Version: All versions >3.4.3

Exception
No exception. Endless loop

To Reproduce
I've prepared a unit test to reproduce bug

		[Test]
		public void EndlessLoopOnQueueCommand ()
		{
			using var stream = new SmtpStream (new DummyNetworkStream (), new NullProtocolLogger ());
			var memory = (MemoryStream) stream.Stream;
			var command = "AUTH GSSAPI YIIkMgYGK"+ new string ('X', 4096);
			stream.QueueCommand (command, default);
		}

Additional context
I've implemented a custom SaslMechanism for GSSAPI Kerberos. So my outgoing blob is greater than 4096 and i have problems which described above.

[jstedfast]

Thanks, I'll try to look into this soon

[alexander-kucherov]

Thanks a lot for your quick fix.
I'm looking forward for a new release.