Distributed scalable database
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Latest commit 19d01e5 Aug 9, 2018

README.md

hyperdb

Distributed scalable database.

npm install hyperdb

Read ARCHITECTURE.md for details on how hyperdb works.

Usage

var hyperdb = require('hyperdb')

var db = hyperdb('./my.db', {valueEncoding: 'utf-8'})

db.put('/hello', 'world', function (err) {
  if (err) throw err
  db.get('/hello', function (err, nodes) {
    if (err) throw err
    console.log('/hello --> ' + nodes[0].value)
  })
})

API

var db = hyperdb(storage, [key], [options])

Create a new hyperdb.

storage can be a string or a function. If a string like the above example, the random-access-file storage module is used; the resulting folder with the data will be whatever storage is set to.

If storage is a function, it will be called with every filename hyperdb needs to operate on. There are many providers for the abstract-random-access interface. e.g.

var ram = require('random-access-memory')
var feed = hyperdb(function (filename) {
  // filename will be one of: data, bitfield, tree, signatures, key, secret_key
  // the data file will contain all your data concattenated.

  // just store all files in ram by returning a random-access-memory instance
  return ram()
})

key is a Buffer containing the local feed's public key. If you do not set this the public key will be loaded from storage. If no key exists a new key pair will be generated.

Options include:

{
  map: node => mappedNode, // map nodes before returning them
  reduce: (a, b) => someNode, // reduce the nodes array before returning it
  firstNode: false, // set to true to reduce the nodes array to the first node in it
  valueEncoding: 'binary' // set the value encoding of the db
}

db.key

Buffer containing the public key identifying this hyperdb.

Populated after ready has been emitted. May be null before the event.

db.discoveryKey

Buffer containing a key derived from the db.key. In contrast to db.key this key does not allow you to verify the data but can be used to announce or look for peers that are sharing the same hyperdb, without leaking the hyperdb key.

Populated after ready has been emitted. May be null before the event.

db.on('ready')

Emitted exactly once: when the db is fully ready and all static properties have been set. You do not need to wait for this when calling any async functions.

db.version(callback)

Get the current version identifier as a buffer for the db.

var checkout = db.checkout(version)

Checkout the db at an older version. The checkout is a DB instance as well. Version should be a version identifier returned by the db.version api or an array of nodes returned from db.heads.

db.put(key, value, [callback])

Insert a new value. Will merge any previous values seen for this key.

db.get(key, callback)

Lookup a string key. Returns a nodes array with the current values for this key. If there is no current conflicts for this key the array will only contain a single node.

db.del(key, callback)

Delete a string key.

db.batch(batch, [callback])

Insert a batch of values efficiently, in a single atomic transaction. A batch should be an array of objects that look like this:

{
  type: 'put',
  key: someKey,
  value: someValue
}

callback's parameters are err, nodes, where nodes is an array of the batched nodes.

db.local

Your local writable feed. You have to get an owner of the hyperdb to authorize you to have your writes replicate. The first person to create the hyperdb is the first owner.

db.authorize(key, [callback])

Authorize another peer to write to the hyperdb.

To get another peer to authorize you you'd usually do something like

myDb.on('ready', function () {
  console.log('You local key is ' + myDb.local.key.toString('hex'))
  console.log('Tell an owner to authorize it')
})

db.authorized(key, [callback])

Check whether a key is authorized to write to the database.

myDb.authorized(otherDb.local.key, function (err, auth) {
  if (err) console.log('err', err)
  else if (auth === true) console.log('authorized')
  else console.log('not authorized')
})

watcher = db.watch(folderOrKey, onchange)

Watch a folder and get notified anytime a key inside this folder has changed.

db.watch('foo/bar', function () {
  console.log('folder has changed')
})

...

db.put('foo/bar/baz', 'hi') // triggers the above

You can destroy the watcher by calling watcher.destroy().

The watcher will emit watching when it starts watching and change when a change has been detected.

If a critical error occurs an error will be emitted on the watcher.

var stream = db.createReadStream(prefix[, options])

Create a readable stream of nodes stored in the database. Set prefix to only iterate nodes prefixed with that folder.

Options include:

{
  recursive: true // visit all subfolders.
                  // set to false to only visit the first node in each folder
  reverse: true   // read the records in reverse order.
  gt: false       // visit only strictly nodes that are > than the prefix
}

var stream = db.createWriteStream()

Create a writable stream.

Where stream.write(data) accepts data as an object or an array of objects with the same form as db.batch().

db.list(prefix[, options], callback)

Same as createReadStream but buffers the result to a list that is passed to the callback.

var stream = db.createDiffStream(prefix[, checkout)

Find out about changes in key/value pairs between the version checkout and current version prefixed by prefix.

stream is a readable object stream that outputs modifications like

{ left: nodes, right: nodes }

left are the nodes for a key found in the db and right are the nodes found in the checkout. If no nodes exist in the db for the key left will be null and vice versa.

var stream = db.createHistoryStream([options])

Returns a readable stream of node objects covering all historic values since the beginning of time.

Nodes are emitted in topographic order, meaning if value v2 was aware of value v1 at its insertion time, v1 must be emitted before v2.

To emit the nodes in reverse order pass {reverse: true} as an option.

var stream = db.createKeyHistoryStream(key)

Returns a readable stream of node objects covering all historic values for a specific key.

Results are returned with the latest value first.

var stream = db.replicate([options])

Create a replication stream. Options include:

{
  live: false // set to true to keep replicating
}

License

MIT