pd-controller

quick and dirty Pure Data process manager for Nodejs

Introduction

pd-controller is a library that spawns pd, pdsend and pdreceive processes, and wraps them into javascript to provide an interface that allows to manage patch instances and communicate with them via TCP.

Here is a simple example :

const Pd = require('pd-controller');
const path = require('path');

// initialize Pd with the `bin` path of pure data
// (where the `pd`, `pdsend`, and `pdreceive` binaries are located)

// on linux this would be Pd.init('/usr/local/bin')
Pd.init('/Applications/Pd-0.49-1-x86_64.app/Contents/Resources/bin')
.then(() => {
    const myPatch = Pd.open(path.join(__dirname, 'hello-increment')); // patch name without '.pd' extension
    myPatch.on('message', (msg) => {
        console.log(`pure data says ${msg}`);
    });
    myPatch.send('hello', 1); // should print "pure data says hello,2" to the console
    Pd.close(myPatch);
});

How it works

When pd-controller is initialized, it kills every running pd, pdsend and pdreceive processes, then spawns one of each, opening two default patches with pd for communication with pdsend and pdreceive and patch instance management.

When opening a patch, pd-controller creates a temporary wrapper .pd file and assigns it a unique id, which is the patch's first argument ($1). Other normal arguments can be passed at instantiation time and retrieved in the patch as $2, $3, etc.

Each patch to be loaded with pd-controller must have an inlet to receive the data sent from the send method in nodejs, and an outlet to send messages which will be emitted as message events in nodejs.

Install pure data on raspbian

Make sure you have the required packages installed

sudo apt-get update -y
sudo apt-get upgrade -y
sudo apt --fix-broken install -y
sudo apt-get install -y build-essential autoconf automake libtool gettext git gcc g++ libasound2-dev libjack-jackd2-dev libfftw3-3 libfftw3-dev make tcl tk

Then download, compile and install pure data

wget http://msp.ucsd.edu/Software/pd-0.49-0.src.tar.gz
tar -xzf pd-0.49-0.src.tar.gz
cd pd-0.49-0
./autogen.sh
./configure --enable-jack --enable-fftw
sudo make install
cd ..

Caveats

Sometimes, when pd-controller is initialized too many times in a short amount of time, thepdsend and pdreceive binaries cannot use the latest TCP port, maybe due to OS restrictions to prevent DDOS attacks. When this happens, the Pd.init() method tries to kill and respawn the binaries every 5 seconds until it succeeds (usually in less than 1 minute), then returns a resolved Promise.

It also happened on a raspberry Pi zero that sending too many messages to pure data in a short amount of time made the node server stop responding without showing any errors. As the communication with pure data happens via TCP by default (using pdsend and pdreceive binaries), the ability to communicate alternatively via UDP (using OSC) was added to the library to avoid overflowing the TCP buffer (if that makes sense), which seemed to work. So for high bandwidth control messages where loss of packets is not an issue (such as real-time sensor data), it is advised to use myPatch.sendUdp('message', value); instead of myPatch.send('message', value); to avoid this inconvenience.