Difference between inbound and outbound sockets in node - node.js

Question

I am writing a function that will make sure a node instance is gracefully shut down.
To do that, I make sure I unref() all sockets. This is what I am doing:
function tidyUp(){
console.log("Closing the server...");
server.close();
console.log("Ordering a hotplate shutdown...");
process.emit( 'hotplateShutdown');
// This will give time to server.close() to actually work..
setTimeout( function() {
console.log("Calling unref() for all Sockets and for the Server:");
wtf.dump();
var handles = Array.prototype.slice.call( process._getActiveHandles() );
handles.forEach( ( h, i ) => {
var name = h.constructor.name;
if( h.unref && typeof h.unref == 'function' & ( name == 'Socket' || name == 'Server' ) ){
console.log("Unreffing:", i );
h.unref();
}
});
console.log("After unreffing:");
wtf.dump();
setTimeout( function(){
console.log("This process should soon close");
console.log("Here is the event queue keeping it alive:");
wtf.dump( true );
}, 1000);
}, 1000 );
};
I am concerned because the server also sends email, and I want to make absolute sure that any that is being sent is indeed sent.
Basically:
"Give a Socket object, how do you tell if it's an INBOUND socket (one receiving connections, as node's HTTP server would open) or an OUTBOUND socket (one open by nodemailer to send an email)."
I will want to unref() all inbound sockets, and leave the outbound ones in peace, till all email has been sent.
Hints?

Answer 1

I ended up keeping track of the inbound sockets opened:
var server = http.createServer(app);
// Keep track of all inbound sockets. They will be
// unref()ed at cleanup time
var inboundSockets = {};
var socketId = 0;
server.on('connection',function( socket ){
socket.__id = socketId ++;
inboundSockets[ socket.__id ] = socket;
socket.on('close',function(){
delete inboundSockets[ socket.__id ];
});
});
process.on('uncaughtException', function (err) {
console.error( "Error caught: ");
console.error(err);
tidyUp();
})
process.on('SIGTERM', function(){
console.log("TERMINATING THIS INSTANCE!");
tidyUp();
});
function tidyUp(){
console.log("Closing the server...");
server.close();
// The next line is important AS IS as it will tell naps that the
// server is no longer functional
console.log("THE SERVER HAS STOPPED");
console.log("Ordering a hotplate shutdown...");
process.emit( 'hotplateShutdown');
// This will give time to server.close() to actually work..
setTimeout( function() {
console.log("Calling unref() for inbound sockets:");
Object.keys( inboundSockets ).forEach( ( __id ) => {
var s = inboundSockets[ __id ];
console.log("Unreffing inbound socket:", s.__id );
s.unref();
});
db.unref();
console.log("After unreffing:");
wtf.dump();
setTimeout( function(){
console.log("This process should soon close");
console.log("Here is the event queue keeping it alive:");
wtf.dump( true );
}, 5000);
}, 1000 );
};
Note that I assign an ID to the socket at creation time (there doesn't seem to be a clear universal way to get a unique ID) and then unref them when the server goes down...