git ssb

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const Actor = require('./actor.js')
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const Scheduler = require('./scheduler.js')
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const {ID} = require('./systemObjects.js')
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const crypto = require('crypto')
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module.exports = class Hypervisor {
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  /**
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   * The Hypervisor manages the container instances by instantiating them and
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   * destorying them when possible. It also facilitates localating Containers
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   * @param {Tree} tree - a [radix tree](https://github.com/dfinity/js-dfinity-radix-tree) to store the state
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   */
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  constructor (tree, nonce = 0) {
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    this.tree = tree
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    this.scheduler = new Scheduler(this)
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    this._containerTypes = {}
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    this.nonce = nonce
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  }
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  /**
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   * sends a message
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   * @param {Object} cap - the capabilitly used to send the message
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   * @param {Object} message - the [message](https://github.com/primea/js-primea-message) to send
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   * @returns {Promise} a promise that resolves once the receiving container is loaded
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   */
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  send (messages) {
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    if (!Array.isArray(messages)) {
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      messages = [messages]
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    }
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    this.scheduler.queue(messages)
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  }
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  async loadActor (id) {
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    const state = await this.tree.get(id.id, true)
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    const [code, storage] = await Promise.all([
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      this.tree.graph.get(state.node, '1'),
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      this.tree.graph.get(state.node, '2')
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    ])
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    const [type, nonce] = state.value
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    const Container = this._containerTypes[type]
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    // create a new actor instance
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    const actor = new Actor({
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      hypervisor: this,
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      state,
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      Container,
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      id,
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      nonce,
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      type,
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      code,
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      storage: storage || [],
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      cachedb: this.tree.dag._dag,
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      tree: this.tree
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    })
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    await actor.startup()
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    return actor
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  }
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  /**
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   * creates an instance of an Actor
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   * @param {Integer} type - the type id for the container
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   * @param {Object} message - an intial [message](https://github.com/primea/js-primea-message) to send newly created actor
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   * @param {Object} id - the id for the actor
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   */
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  async createActor (type, code, id = {nonce: this.nonce++, parent: null}) {
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    const Container = this._containerTypes[type]
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    const encoded = encodedID(id)
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    let idHash = this._hash(encoded)
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    idHash = new ID(idHash)
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    const module = await Container.onCreation(code, idHash, this.tree)
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    const metaData = [type, 0]
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    // save the container in the state
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    const node = await this.tree.set(idHash.id, metaData)
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    // save the code
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    node[1] = {
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      '/': code
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    }
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    // save the storage
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    node[2] = {
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      '/': []
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    }
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    return {
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      id: idHash,
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      module
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    }
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  }
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  _hash (buf) {
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    const hash = crypto.createHash('sha256')
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    hash.update(buf)
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    return hash.digest().slice(0, 20)
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  }
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  /**
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   * creates a state root starting from a given container and a given number of
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   * ticks
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   * @param {Number} ticks the number of ticks at which to create the state root
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   * @returns {Promise}
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   */
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  createStateRoot () {
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    return new Promise((resolve, reject) => {
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      this.scheduler.on('idle', () => {
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        this.tree.flush().then(resolve)
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      })
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    })
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  }
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  /**
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   * regirsters a container with the hypervisor
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   * @param {Class} Constructor - a Class for instantiating the container
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   * @param {*} args - any args that the contructor takes
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   * @param {Integer} typeId - the container's type identification ID
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   */
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  registerContainer (Constructor) {
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    this._containerTypes[Constructor.typeId] = Constructor
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  }
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}
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function encodedID (id) {
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  const nonce = Buffer.from([id.nonce])
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  if (id.parent) {
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    return Buffer.concat([nonce, id.parent.id])
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  } else {
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    return nonce
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  }
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}
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