chibenwa opened a new pull request #908:
URL: https://github.com/apache/james-project/pull/908
## Why?
- Core handlers are blocking and one should never block on the event loop.
- Order of outgoing messages is not preserved for items sent from threads
within and out of the event loop
## Current caveats
https://gitter.im/netty/netty?at=62257c72d1b64840db5467af
Currently I encounter issues with SMTP pipelining: the client sends all the
SMTP requests into a single network hop.
```
Socket client = new
Socket(bindedAddress.getAddress().getHostAddress(), bindedAddress.getPort());
buf.append("HELO TEST");
buf.append("\r\n");
buf.append("MAIL FROM: <test@localhost>");
buf.append("\r\n");
buf.append("RCPT TO: <test2@localhost>");
buf.append("\r\n");
buf.append("DATA");
buf.append("\r\n");
buf.append("Subject: test");
buf.append("\r\n");
buf.append("\r\n");
buf.append("content");
buf.append("\r\n");
buf.append(".");
buf.append("\r\n");
buf.append("quit");
buf.append("\r\n");
OutputStream out = client.getOutputStream();
out.write(buf.toString().getBytes());
out.flush();
```
CF
https://github.com/apache/james-project/blob/634be36800422259e40121248fb0d07475024a9c/server/protocols/protocols-smtp/src/test/java/org/apache/james/smtpserver/SMTPServerTest.java#L1887
The way `DATA` is handled is that it adds a handler prior the core SMTP
handler:
https://github.com/chibenwa/james-project/blob/ffc0d4a8b22508b8f5b58594d14041d1f6bc3acf/protocols/netty/src/main/java/org/apache/james/protocols/netty/NettyProtocolTransport.java#L162
```
channel.pipeline().addBefore(eventExecutors,
HandlerConstants.CORE_HANDLER, "lineHandler" + lineHandlerCount, new
LineHandlerUpstreamHandler(session, overrideCommandHandler));
```
Everything works fine if the core handler is running on the event loop,
however once we switch it to a distinct executor, the pipeline modification is
no longer applied and the subsequent message content is interpreted as SMTP
commands as it the line handler was not there.
CF
https://github.com/chibenwa/james-project/blob/ffc0d4a8b22508b8f5b58594d14041d1f6bc3acf/protocols/netty/src/main/java/org/apache/james/protocols/netty/AbstractChannelPipelineFactory.java#L78
```
// Fails
pipeline.addLast(eventExecutorGroup, HandlerConstants.CORE_HANDLER,
createHandler());
// Succeed
pipeline.addLast(HandlerConstants.CORE_HANDLER, createHandler());
```
Is there any way to modify the pipeline 'synchronously' from outside the
event loop?
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