@coboxcoop/multifeed

@coboxcoop/multifeed

Fork of https://github.com/@frando/multifeed#corestore, which is a fork of https://github.com/kappa-db/multifeed

Multifeed lets you group together a local set of hypercores with a remote set of hypercores under a single shared identifier or key.

It solves the problem of Hypercore only allowing one writer per hypercore by making it easy to manage and sync a collection of hypercores -- by a variety of authors -- across peers.

Replication works by extending the regular hypercore exchange mechanism to include a meta-exchange, where peers share information about the feeds they have locally, and choose which of the remote feeds they'd like to download in exchange. Right now, the replication mechanism defaults to sharing all local feeds and downloading all remote feeds.

This fork of multifeed removes storage of hypercores from multifeed, instead delegating / passing this on to corestore. Multifeed now caches each feed using its given public key to ensure the correct feeds are shared on replication with remote peers. Feeds keys are persisted in an additional local-only hypercore (it is not shared during replication), so that a multifeed instance can be easily recomposed from our corestore, which holds no knowledge of which core belongs to which multifeed.

Using corestore-swarm-networking and the new multifeed networker, we can apply granular replication logic for several multifeeds across a single instance of the Hyperswarm DHT.

Usage

Simple

var Multifeed = require('multifeed')
var ram = require('random-access-memory')

var multi = new Multifeed('./db', { valueEncoding: 'json' })

// a multifeed starts off empty
console.log(multi.feeds().length)             // => 0

// create as many writeable feeds as you want; returns hypercores
multi.writer('local', function (err, w) {
  console.log(w.key, w.writeable, w.readable)   // => Buffer <0x..> true true
  console.log(multi.feeds().length)             // => 1

  // write data to any writeable feed, just like with hypercore
  w.append('foo', function () {
    var m2 = multifeed(hypercore, ram, { valueEncoding: 'json' })
    m2.writer('local', function (err, w2) {
      w2.append('bar', function () {
        replicate(multi, m2, function () {
          console.log(m2.feeds().length)        // => 2
          m2.feeds()[1].get(0, function (_, data) {
            console.log(data)                   // => foo
          })
          multi.feeds()[1].get(0, function (_, data) {
            console.log(data)                   // => bar
          })
        })
      })
    })
  })
})

function replicate (a, b, cb) {
  let pending = 2

  var r = a.replicate()

  r.pipe(b.replicate()).pipe(r)
    .once('error', cb)
    .once('remote-feeds', done)
    .once('remote-feeds', done)

  function done () {
    if (!--pending) return cb()
  }
}

Complex

const Corestore = require('corestore')
const SwarmNetworker = require('corestore-swarm-networking')
const Multifeed = require('multifeed')
const Networker = require('multifeed/networker')
const crypto = require('hypercore-crypto')

// create a new corestore for our hypercores
const corestore = new Corestore(ram)

// initialize hyperswarm using corestore-swarm-networker and configure for multifeed
const network = new Networker(new SwarmNetworker(corestore))

// create two separate instances of multifeed for use across a single network swarm
const multi1 = new Multifeed(corestore, { key: crypto.randomBytes(32) })
const multi2 = new Multifeed(corestore, { key: crypto.randomBytes(32) })

// start replicating
network.swarm(multi1)
network.swarm(multi2)

// create a third instance which shares a key with the first
const multi3 = new Multifeed(corestore, { key: multi1.key })

// multi1 and multi3 will now replicate feeds
network.swarm(multi3)

For more information on how to implement replication across multiple multifeeds, see test/new-basic.js for an example.

The main export (new Multifeed(storage, opts)) is API compatible with the original Multifeed as documented below. storage can also be a corestore (otherwise one is created with storage). Then connect it to a corestore swarm networker to apply multifeed replication.

API

var multifeed = require('multifeed')

var multi = multifeed(storage[, opts])

Pass in a random-access-storage backend, and options. Included opts are passed into new hypercores created, and are the same as hypercore's.

Valid opts include:

• opts.encryptionKey (string): optional encryption key to use during replication. If not provided, a default insecure key will be used.
• opts.hypercore: constructor of a hypercore implementation. hypercore@8.x.x is used from npm if not provided.

multi.writer([name], [options], cb)

If no name is given, a new local writeable feed is created and returned via cb.

If name is given and was created in the past on this local machine, it is returned. Otherwise it is created. This is useful for managing multiple local feeds, e.g.

var main = multi.writer('main')        // created if doesn't exist
var content = multi.writer('content')  // created if doesn't exist

main === multi.writer('main')          // => true

options is an optional object which may contain:

• options.keypair - an object with a custom keypair for the new writer. This should have properties keypair.publicKey and keypair.secretKey, both of which should be buffers.

var feeds = multi.feeds()

An array of all hypercores in the multifeed. Check a feed's key to find the one you want, or check its writable / readable properties.

Only populated once multi.ready(fn) is fired.

var feed = multi.feed(key)

Fetch a feed by its key key (a Buffer or hex string).

var stream = multi.replicate(isInitiator, [opts])

Create an encrypted duplex stream for replication.

Ensure that isInitiator to true to one side, and false on the other. This is necessary for setting up the encryption mechanism.

Works just like hypercore, except all local hypercores are exchanged between replication endpoints.

stream.on('remote-feeds', function () { ... })

Emitted when a new batch (1 or more) of remote feeds have begun to replicate with this multifeed instance.

This is useful for knowing when multi.feeds() contains the full set of feeds from the remote side.

multi.on('feed', function (feed, name) { ... })

Emitted whenever a new feed is added, whether locally or remotely.

multi.close(cb)

Close all file resources being held by the multifeed instance. cb is called once this is complete.

multi.closed

true if close() was run successfully, falsey otherwise.

Errors

The duplex stream returned by .replicate() can emit, in addition to regular stream errors, two fatal errors specific to multifeed:

• ERR_VERSION_MISMATCH

  • err.code = 'ERR_VERSION_MISMATCH'
  • err.usVersion = 'X.Y.Z' (semver)
  • err.themVersion = 'A.B.C' (semver)

• ERR_CLIENT_MISMATCH

  • err.code = 'ERR_CLIENT_MISMATCH'
  • err.usClient = 'MULTIFEED'
  • err.themClient = '???'

Install

With npm installed, run

$ npm install @frando/corestore-multifeed

See Also

• multifeed (original)
• multifeed-index
• hypercore
• kappa-core

License

ISC