quitCloseConnection does not close connection

[computerlove]

Version

Vert.x mail-client 4.2.1, Quarkus 2.5.0

Context

When using connection pooling with smtp.office365.com an error is logged every time a connection has reached keep alive-timeout.
(if timeout is set to 60 seconds, the error is printed ~60s after last email is sent)

2021-11-29 12:24:25,510 ERROR [io.ver.ext.mai.imp.SMTPConnection] (vert.x-eventloop-thread-3) Connection reset

With debug logging:

2021-11-29T11:09:49.252+0100 ERROR [vert.x-eventloop-thread-2] io.vertx.ext.mail.impl.SMTPConnection Connection reset: java.net.SocketException: Connection reset
	at java.base/sun.nio.ch.SocketChannelImpl.throwConnectionReset(SocketChannelImpl.java:367)
	at java.base/sun.nio.ch.SocketChannelImpl.read(SocketChannelImpl.java:398)
	at io.netty.buffer.PooledByteBuf.setBytes(PooledByteBuf.java:253)
	at io.netty.buffer.AbstractByteBuf.writeBytes(AbstractByteBuf.java:1132)
	at io.netty.channel.socket.nio.NioSocketChannel.doReadBytes(NioSocketChannel.java:350)
	at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:151)
	at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:719)
	at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:655)
	at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:581)
	at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:493)
	at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:986)
	at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)
	at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
	at java.base/java.lang.Thread.run(Thread.java:832)
: java.net.SocketException: Connection reset
	at java.base/sun.nio.ch.SocketChannelImpl.throwConnectionReset(SocketChannelImpl.java:367)
	at java.base/sun.nio.ch.SocketChannelImpl.read(SocketChannelImpl.java:398)
	at io.netty.buffer.PooledByteBuf.setBytes(PooledByteBuf.java:253)
	at io.netty.buffer.AbstractByteBuf.writeBytes(AbstractByteBuf.java:1132)
	at io.netty.channel.socket.nio.NioSocketChannel.doReadBytes(NioSocketChannel.java:350)
	at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:151)
	at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:719)
	at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:655)
	at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:581)
	at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:493)
	at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:986)
	at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)
	at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
	at java.base/java.lang.Thread.run(Thread.java:832)

Stepping though SMTPConnection.quitCloseConnection I can see that QUIT is sent, but the connection is not closed.

The javadoc for quitCloseConnection says

send QUIT and close the connection

So my interpretation is that calling shutdown() is missing in quitCloseConnection. If I call shutdown() after QUIT i sent the connection reset does not happen.

Do you have a reproducer?

https://github.com/computerlove/mailer-reproducer

Steps to reproduce

1. Setup a account for smtp.office365.com
2. Fill account properties in application.properties
3. mvnw quarkus:dev
4. curl localhost:8080/hello
5. After ~60s ERROR Connection reset should be logged.

[gaol]

It looks to me that the smtp server does not reply before closing the connection, which it should do according to https://datatracker.ietf.org/doc/html/rfc5321#section-4.1.1.10

I will check it next week after my current list, thanks.

[gaol]

I can reproduce the error logging, and it seems the smtp server does reply on the QUIT command with 221 2.0.0 Service closing transmission channel, so it is fine.

For some reason, the exceptionHandler of the underline NetSocket gets called after the client gets the response, that is where the error logging comes from.

[gaol]

I see [RST, ACK] sequence in Wireshark, which indicates that the smtp server does not close the connection gracefully. I don't see this error logging with local Apache James server setup, it closes the connection gracefully with [FIN, ACK] flags.

I don't see much we can do in mail client side except ignoring the exception if QUIT has been sent to smtp server.