Function _duplexify

lib/internal/streams/duplexify.js:258–389

(pair)

}

function _duplexify(pair) {
  const r = pair.readable && typeof pair.readable.read !== 'function' ?
    Readable.wrap(pair.readable) : pair.readable;
  const w = pair.writable;

  let readable = !!isReadable(r);
  let writable = !!isWritable(w);

  let ondrain;
  let onfinish;
  let onreadable;
  let onclose;
  let d;

  function onfinished(err) {
    const cb = onclose;
    onclose = null;

    if (cb) {
      cb(err);
    } else if (err) {
      d.destroy(err);
    }
  }

  // TODO(ronag): Avoid double buffering.
  // Implement Writable/Readable/Duplex traits.
  // See, https://github.com/nodejs/node/pull/33515.
  d = new Duplexify({
    // TODO (ronag): highWaterMark?
    readableObjectMode: !!r?.readableObjectMode,
    writableObjectMode: !!w?.writableObjectMode,
    readable,
    writable,
  });

  if (writable) {
    eos(w, (err) => {
      writable = false;
      if (err) {
        destroyer(r, err);
      }
      onfinished(err);
    });

    d._write = function(chunk, encoding, callback) {
      if (w.write(chunk, encoding)) {
        callback();
      } else {
        ondrain = callback;
      }
    };

    d._final = function(callback) {
      w.end();
      onfinish = callback;
    };