NodeJS receiving data from PHP server - php

Question

I'm currently working on a simple NodeJS client that connects to a PHP server using the net classes. In addition, the NodeJS client is working as a Socket.IO server that sends data received from the PHP server to the browsers connected with Socket.IO.
So far, everything is working fine. Yet if I connect with another client to Socket.IO, the PHP server has to send a notification to every connected client. Thus, it sends a JSON-encoded array to the NodeJS client which processes the JSON data (decoding and modifying it a bit).
Now the problem is that sometimes two separate messages sent by the PHP server are concatenated in NodeJS' onData event handling function:
client.on("data", function(data) {
var msgData = JSON.parse(data.toString("utf8"));
[...]
}
The variable data now sometimes (not every time!) contains two JSON-strings, such as:
{ "todo":"message", [...] } { "todo":"message", [...] }
This of course results in an exception thrown by the JSON.parse function. I expected two calls of the onData-function with the variable data being:
{ "todo":"message", [...] }
On the PHP server side I have to iterate over an array containing all Socket.IO-connections that are currently served:
foreach($sockets as $id => $client) {
$nodeJS->sendData($client, array("todo" => "message", [...]);
}
The $nodeJS->sendData-function json-encodes the array and sends it to the NodeJS client:
socket_write($nodeClient, json_encode($dataToSend));
The $nodeJS->sendData function is definitively called two times, as socket_write is.
I now have no idea whether PHP or NodeJS concatenates those two strings. What I want, is that NodeJS calls the onData-handler once for each time the $nodeJS->sendData function is called (e.g. sendData is called twice → the onData-event is fired twice).
I could of course add some flag at the end of each json-encoded string and later split them into an array in the onData function. However, I don't like that solution much.
Is there an easier way to accomplish this?

Answer 1

It's important to remember that when you're reading from a socket, the data is going to come in arbitrary chunks and its entirely up to your code to split them up into units that are meaningful to process; there is absolutely no guarantee that each chunk will correspond to one meaningful unit.
yannisgu has given you the first part of the solution (terminate each unit with a newline, so your code can tell where it ends): now you need to implement the second part, which is to buffer your incoming data and split it into units.
At initialization, do something like
var buf = '';
and set client's encoding to utf8.
In your "data" handler:
[UPDATED: incorporated josh3736's suggestions]
buf += data;
var idx;
while ((idx = buf.indexOf('\n')) >= 0) {
// there's at least one complete unit buffered up
var unit = buf.slice(0, idx);
// extract it
if (unit.slice(-1) == '\r') {
// CRLF delimited
unit = unit.slice(0, -1);
}
if (unit.length) {
// ignore empty strings
var msgData = JSON.parse(unit);
[...]
// process it
}
buf = buf.slice(idx +1);
// discard it
}
// at this point, buf is either empty or contains an incomplete
// unit which will be processed as soon as the rest of it comes in

Answer 2

Try to add a new line after the JSON-String on the PHP side.