SslStream.WriteAsync() hangs on 0-byte WriteAsync on Linux and macOS

[cesarblum]

To repro, connect to any SSL endpoint (127.0.0.1:5001 in the example below) and attempt a 0-byte write:

using System;
using System.IO;
using System.Net.Security;
using System.Net.Sockets;
using System.Security.Authentication;
using System.Security.Cryptography.X509Certificates;
using System.Threading;

namespace ConsoleApplication
{
    public class Program
    {
        public static void Main(string[] args)
        {
            var x509certificate = new X509Certificate2(@"testCert.pfx", "testPassword");

            using (var client = new TcpClient())
            {
                client.ConnectAsync("127.0.0.1", 5001).Wait();

                using (var sslStream = new SslStream(client.GetStream(), false, (sender, certificate, chain, errors) => true,
                    (sender, host, certificates, certificate, issuers) => x509certificate))
                {
                    sslStream.AuthenticateAsClientAsync("localhost", new X509CertificateCollection(), SslProtocols.Tls12 | SslProtocols.Tls11, false).Wait();
                    sslStream.WriteAsync(new byte[0], 0, 0, CancellationToken.None).Wait();
                }
            }
        }
    }
}

It just hangs there.

We found this issue in Kestrel, which is experiencing test failures because of this (aspnet/KestrelHttpServer#1193 (comment)). Kestrel is hanging in https://github.com/aspnet/KestrelHttpServer/blob/4337d2a4a751ee7ccb0e0c460670c0abd044d040/src/Microsoft.AspNetCore.Server.Kestrel/Filter/Internal/StreamSocketOutput.cs#L63 when we do a 0-byte write to flush.

[stephentoub]

Do you have this fix?
dotnet/corefx#13083
dotnet/corefx#13095

[cesarblum]

Is that fix in System.Net.Security 4.3.0? When I revert to 4.3.0-preview1-24530-04 I don't see the issue.

[stephentoub]

Oh, shoot, you probably do, and those fixes look busted:
@bartonjs, don't we need to complete the IAsyncResult instance rather than just returning when the count is 0?