wormhole-crypto/lib/slice-transformer.js

Streaming encryption for Wormhole.app, based on Encrypted Content-Encoding for HTTP (RFC 8188)

/* eslint-env browser */

/**
 * Tranform stream that outputs chunks of a specific size. Final chunk may be
 * less than the desired size.
 *
 * firstChunkSize: The size of the first chunk
 * restChunkSize:  The size of all subsequent chunks, optional. If omitted, the
 *                 size of subsequenct chunks will be same as `firstChunkSize`
 */

export class SliceTransformer {
  constructor (firstChunkSize, restChunkSize) {
    this.chunkSize = firstChunkSize
    this.restChunkSize = restChunkSize || firstChunkSize

    this.partialChunk = new Uint8Array(this.chunkSize)
    this.offset = 0 // offset into `partialChunk`
  }

  send (record, controller) {
    controller.enqueue(record)
    this.chunkSize = this.restChunkSize
    this.partialChunk = new Uint8Array(this.chunkSize)
    this.offset = 0
  }

  transform (chunk, controller) {
    let i = 0 // offset into `chunk`

    if (this.offset > 0) {
      const len = Math.min(chunk.byteLength, this.chunkSize - this.offset)
      this.partialChunk.set(chunk.subarray(0, len), this.offset)
      this.offset += len
      i += len

      if (this.offset === this.chunkSize) {
        this.send(this.partialChunk, controller)
      }
    }

    while (i < chunk.byteLength) {
      const remainingBytes = chunk.byteLength - i
      if (remainingBytes >= this.chunkSize) {
        const record = chunk.slice(i, i + this.chunkSize)
        i += this.chunkSize
        this.send(record, controller)
      } else {
        const end = chunk.slice(i, i + remainingBytes)
        i += end.byteLength
        this.partialChunk.set(end)
        this.offset = end.byteLength
      }
    }
  }

  flush (controller) {
    if (this.offset > 0) {
      controller.enqueue(this.partialChunk.subarray(0, this.offset))
    }
  }
}