multifeed

multi-writer hypercore

Small module that manages multiple hypercores: feeds you create locally are writeable, others' are readonly. Replicating with another multifeed peers exchanges the content of all of the hypercores.

Usage

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

var multi = multifeed(hypercore, './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) {
  var r = a.replicate()
  r.pipe(b.replicate()).pipe(r)
    .once('end', cb)
    .once('error', cb)
}

API

var multifeed = require('multifeed')

var multi = multifeed(hypercore, storage[, opts])

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

multi.writer([name, ]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

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([opts])

Create a duplex stream for replication.

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

Note: this stream is not an encrypted channel.

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

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

Install

With npm installed, run

$ npm install multifeed

Replicaton Policies

You can control what gets replicated by providing a policy as a plugin:

var multi = multifeed(hypercore, './db', { valueEncoding: 'json' })
multi.use({
  init: function(multifeed) {
    // called on multifeed.ready
    // use it for initalization.
  },
  have: function(local, share) {
    // called on peer connection
    // select which feeds to share
    share(local.keys, {
      random: local.keys.map(function() { return Math.random() - 0.5 })
    })
  },
  want: function(remote, request) {
    // called when remote peer's
    // share list is available.
    // remote.keys is always available
    // remote contains also all custom props sent by remote.
    var keys = remote.keys.filter(function(k, i){
        return remote.random[i] > 0.5
    })
    request(keys)
  }
})

See Also

• multifeed-index
• hypercore
• kappa-core

License

ISC