truncated messages on tcp port due to split data on socket event

[rwrnet]

NodeJS: v14.13.1.

I chased an non-consistend issue of wrong data in a communication with an Inverter down to a clear reason with this simple example code:

var client = new net.Socket();
client.on('data', function(data) {
	console.log('Received: ' + data.toString("hex"));
});
client.connect(502, '10.0.2.244', function() {
	console.log('Connected');
	client.write(Buffer.from("000100000006030378530002","hex"));
});

The output is sometimes:

Received: 000100000007030304000013
Received: 88

So NodeJS Socket emits two messages but on Wireshark one can clearly see, this was sent by the inverter in one response:

0000   03 04 00 00 13 88

Unfortunately the tcpport receiver doesn't handle this correctly and instead creates a message of the original size (from the message header) which then get filled up by a 0-byte ending in a payload of 13 00 instead of the expected 13 88: https://github.com/yaacov/node-modbus-serial/blob/master/ports/tcpport.js#L54

So I guess, the code needs to decouple Socket emits from Modbus emits. I'm neither a Modbus nor a nodejs crack, but if you don't mind to support me, I can work on a PR.

[martinjamilis]

Hi, I'm facing the same issue, did you find a solution?

[rwrnet]

As a workaround, pull a byte more than needed and just ignore the extra byte when parsing the result. But I hate workarounds. ;)

[AuspeXeu]

See #396