appendInitVect.js

const { Transform } = require('stream');

class AppendInitVect extends Transform {
  constructor(initVect, opts) {
    super(opts);
    this.initVect = initVect;
    this.appended = false;
  }

  _transform(chunk, encoding, cb) {
    if (!this.appended) {
      this.push(this.initVect);
      this.appended = true;
    }
    this.push(chunk);
    cb();
  }
}

module.exports = AppendInitVect;

Surely this prepends the IV. Regardless, thanks.

Yeah, the language is weird depending on how you think about it. If you think of it like an array that already exists that want to push something onto it, you would append. For example, (in python):

xs = []
xs.append(0)

Even though 0 is the first thing, we're appending.