get length () {
    if (this.has('Content-Length')) {
      return parseInt(this.get('Content-Length'), 10) || 0
    }

    const { body } = this
    if (!body || isStream(body)) return undefined
    if (typeof body === 'string') return Buffer.byteLength(body)
    if (Buffer.isBuffer(body)) return body.length
    return Buffer.byteLength(JSON.stringify(body))
  }
Return parsed response Content-Length when present.

@return {Number}
@api public