What's the proper way to handle back-pressure in a node.js Transform stream?

Question

Intro

These are my first adventures in writing node.js server side. It\'s been fun so far but I\'m having some difficulty understanding the proper way to implement

Answer 1

Mike Lippert's answer is the closest to the truth, I think. It appears that waiting for a new _read() call to begin again from the reading stream is the only way that the Transform is actively notified that the reader is ready. I wanted to share a simple example of how I override _read() temporarily.

_transform(buf, enc, callback) {

  // prepend any unused data from the prior chunk.
  if (this.prev) {
    buf = Buffer.concat([ this.prev, buf ]);
    this.prev = null;
  }

  // will keep transforming until buf runs low on data.
  if (buf.length < this.requiredData) {
    this.prev = buf;
    return callback();
  }

  var result = // do something with data...
  var nextbuf = buf.slice(this.requiredData);

  if (this.push(result)) {
    // Continue transforming this chunk
    this._transform(nextbuf, enc, callback);
  }
  else {
    // Node is warning us to slow down (applying "backpressure")
    // Temporarily override _read request to continue the transform
    this._read = function() {
        delete this._read;
        this._transform(nextbuf, enc, callback);
    };
  }
}