node.js net module pings and messages not happening

Question

I have two node.js applications running side by side on my server and I wan't to send server-side messages between them in a light weight manner using native node.js (v0.10.33) module net

I intend the first application to send messages to the second. I see the console log listening...,

In the first application:

var push='';
var net=require('net');
var server=net.createServer(function(p){
    p.on('error',function(err){console.log(err);});
    push=p;
    setInterval(function(){push.write(JSON.stringify({'f':'ping','data':'stay alive'}));},1000);
    });
server.listen(8008,function(){console.log('listening...')});

//a real message might be sent later in the application (this example would need a setTimeout)
push.write(JSON.stringify({'f':'msg','data':'Hello World'}));

In the second application I see the console log open

var net=require('net');
var pull=new net.Socket();
pull.connect(8008,'127.0.0.1',function(){console.log('open');
pull.on('data',function(_){
    _=JSON.parse(_);
    if(_.f==='ping'){console.log('!!!ping!!!');}
    else{console.log(_.data);}
    });
pull.on('error',function(err){console.log('pull: '+err);});
});

I do not see any other activity though (no pings, and later after the open event, no hello world) and no errors.

If I inspect with console.dir(pull) I don't see events for accepting data ie: ondata or onmessage

What is wrong?

score 0 · Accepted Answer · edited May 23 '17 at 10:25

Unfortunately, I must point out that this messaging scheme is fundamentally broken. You're using TCP, which provides a stream of bytes, not messages.

Despite the fact that TCP sends its data over IP packets, TCP is not a packet protocol. A TCP socket is simply a stream of data. Thus, it is incorrect to view the data event as a logical message. In other words, one socket.write on one end does not equate to a single data event on the other. A single data event might contain multiple messages, a single message, or only part of a message.

The good news is this is a problem already solved many times over. I'd recommend either:

Using a library meant for passing JSON messages over TCP.
Using something like redis as a pub-sub messaging solution (this option makes your app much easier to scale)
If you know that your two apps will always run on the same machine, you should use node's built-in IPC mechanism.

node.js net module pings and messages not happening

1 Answers1