hyper-beats/lib/encoding.js

Decentralised music using hypercore

const cenc = require('compact-encoding')
const safetyCatch = require('safety-catch')

const BEATS_METADATA_VERSION_MAJOR = 1
const BEATS_METADATA_VERSION_MINOR = 0

const BeatsMetadataEnc = {
  preencode (state, m) {
    cenc.string.preencode(state, 'HYPERBEATS')
    cenc.uint.preencode(state, BEATS_METADATA_VERSION_MAJOR)
    cenc.uint.preencode(state, BEATS_METADATA_VERSION_MINOR)
    cenc.string.preencode(state, m.mimeType)
    cenc.uint.preencode(state, m.framesPerBlock)
    cenc.uint.preencode(state, m.bytesPerFrame)
  },

  encode (state, m) {
    cenc.string.encode(state, 'HYPERBEATS')
    cenc.uint.encode(state, BEATS_METADATA_VERSION_MAJOR)
    cenc.uint.encode(state, BEATS_METADATA_VERSION_MINOR)
    cenc.string.encode(state, m.mimeType)
    cenc.uint.encode(state, m.framesPerBlock)
    cenc.uint.encode(state, m.bytesPerFrame)
  },

  decode (state) {
    try {
      const dataType = cenc.string.decode(state)
      if (dataType !== 'HYPERBEATS') {
        throw new Error('No hyperbeats here')
      }

      const version = {
        major: cenc.uint.decode(state),
        minor: cenc.uint.decode(state)
      }
      if (version.major !== BEATS_METADATA_VERSION_MAJOR) {
        throw new Error('Incompatible Hyperbeats version')
      }

      return {
        version,
        mimeType: cenc.string.decode(state),
        framesPerBlock: cenc.uint.decode(state),
        bytesPerFrame: cenc.uint.decode(state)
      }
    } catch (e) { // TODO: differentiate between errors
      safetyCatch(e)
      throw new Error(`The core does not contain valid hyperbeats (version ${BEATS_METADATA_VERSION_MAJOR}.${BEATS_METADATA_VERSION_MINOR})`)
    }
  }
}

module.exports = {
  BeatsMetadataEnc
}