code: function writeOrBuffer(stream, state, isBuf, chunk, encoding, cb) {
    if (!isBuf) {
      chunk = decodeChunk(state, chunk, encoding);
      if (Buffer.isBuffer(chunk)) encoding = 'buffer';
    }
    var len = state.objectMode ? 1 : chunk.length;
  
    state.length += len;
  
    var ret = state.length < state.highWaterMark;
    // we must ensure that previous needDrain will not be reset to false.
    if (!ret) state.needDrain = true;
  
    if (state.writing || state.corked) {
      var last = state.lastBufferedRequest;
      state.lastBufferedRequest = new WriteReq(chunk, encoding, cb);
      if (last) {
        last.next = state.lastBufferedRequest;
      } else {
        state.bufferedRequest = state.lastBufferedRequest;
      }
      state.bufferedRequestCount += 1;
    } else {
      doWrite(stream, state, false, len, chunk, encoding, cb);
    }
  
    return ret;
  }
docs: if we're already writing something, then just put this in the queue, and wait our turn.  Otherwise, call _write If we return false, then we need a drain event, so set that flag.