@dswarm/dht

The DHT powering the dSwarm stack

npm install @dswarm/dht

Usage

const dht = require('@dswarm/dht')
const crypto = require('crypto')

const node = dht({
  // just join as an ephemeral node
  // as we are shortlived
  ephemeral: true
})

const topic = crypto.randomBytes(32)

// announce a port
node.announce(topic, { port: 12345 }, function (err) {
  if (err) throw err

  // try and find it
  node.lookup(topic)
    .on('data', console.log)
    .on('end', function () {
      // unannounce it and shutdown
      node.unannounce(topic, { port: 12345 }, function () {
        node.destroy()
      })
    })
})

API

const node = dht([options])

Create a new dWeb DHT node.

Options include:

{
  // Optionally overwrite the default bootstrap servers
  bootstrap: ['host:port'],
  // If you are a shortlived client or don't want to host
  // data join as an ephemeral node. (defaults to false)
  ephemeral: true,
  // if set to true, the adaptive option will cause the
  // node to become non-ephemeral after the node has shown
  // to be long-lived (defaults to false)
  adaptive: true,
  // time until a peer is dropped
  maxAge: 12 * 60 * 1000
}

Note: The default bootstrap servers are publicly served on behalf of the commons. To run a fully private DHT, start two or more dht nodes with an empty bootstrap array (dht({bootstrap:[]})) and then use the addresses of those nodes as the bootstrap option in all other dht nodes.

node.holepunch(peer, [callback])

UDP holepunch to another peer.

peer should be a { host, port, referrer: { host, port } }, where referrer should be the host and port of the DHT node who told you about this peer.

const stream = node.lookup(topic, [options], [callback])

Look for peers in the DHT on the given topic. Topic should be a 32 byte buffer (normally a hash of something).

Options include:

{
  // Optionally set your public port. This will make
  // other peers no echo back yourself
  port: 12345,
  // Optionally look for LAN addresses as well by
  // passing in your own. Will also exclude yourself from
  // the results. Only LAN addresses announced on the
  // same public IP and sharing the first two parts (192.168)
  // will be included.
  localAddress: {
    host: '192.168.100.100',
    port: 20000
  }
}

The returned stream looks like this

{
  // The DHT node that is returning this data
  node: { host, port },
  // List of peers
  peers: [ { host, port }, ... ],
  // List of LAN peers
  localPeers: [ { host, port }, ... ]
}

If you pass the callback the stream will be error handled and buffered.

const stream = node.announce(topic, [options], [callback])

Announce a port to the dht.

Options include:

{
  // Explicitly set the port you want to announce.
  // Per default you UDP socket port is announced.
  port: 12345,
  // Optionally announce a LAN address as well.
  // Only people with the same public IP as you will
  // get these when doing a lookup
  localAddress: {
    host: '192.168.100.100',
    port: 20000
  }
}

An announce does a parallel lookup so the stream returned looks like the lookup stream. If you pass a callback the stream will be error handled and buffered.

node.unannounce(topic, [options], [callback])

Unannounce a port. Takes the same options as announce.

node.destroy()

Fully destroy this DHT node.

node.listen([port])

Explicitly listen on a UDP port. If you do not call this it will use a random free port.

node.immutable.put(value, callback = (err, key) => {}) => stream

Store an immutable value in the DHT. When successful, the second argument passed to callback contains the generated key (a hash) for that value.

node.immutable.get(key, callback = (err, value, info) => {}) => stream

Fetch an immutable value from the DHT. When successful, the second argument passed to callback contains the resolved value. The third argument info is an object containing id which is the ID of the responding Node.

node.immutable.get(key) => stream

Fetch all matching immutable values from the DHT.

Any values found are emitted in a data event where the data object takes the form: {id, value}. The id is the ID of the responding Node.

node.mutable.keypair()

Use this method to generate the required keypair for a put. Returns an object with {publicKey, secretKey}. publicKey holds a public key buffer, secretKey holds a private key buffer.

node.mutable.salt([str, ]size = 32)

Utility method for creating a random or hashed salt value.

If called with a string the string will be hashed, to a generic hash of size length.

If called without any inputs, or with a number, random bytes of size length will be generated.

The salt can optionally be passed in mutable.put and mutable.get options. Salt values can be used as a sort of secondary UID, allowing multiple values to be stored under the same public key. Min size is 16 bytes, max size is 64 bytes.

node.mutable.sign(value, options)

Utility method which can be used to create a signature.

The options are the exact same as those of mutable.put (except signature).

Options:

• keypair – REQUIRED, use node.mutable.keypair to generate this.
• salt - OPTIONAL - default undefined, a buffer <= 64 bytes. If supplied it will salt the signature used to verify mutable values.

node.mutable.signable(value, options)

Utility method which returns the exact buffer that would be signed in mutable.put (that does not provide a signature). This is only needed when using a salt, otherwise it will return the same value passed in. This method is to facilitate out-of-band signing (e.g. hardware signing), do not pass the returned signable value into mutable.sign, mutable.sign already uses mutable.signable.

Options:

• salt - OPTIONAL - default undefined, a buffer <= 64 bytes. If supplied it will salt the signature used to verify mutable values.
• seq - OPTIONAL - default 0, a number which should be increased every time put is passed a new value for the same keypair

node.mutable.put(value, options, callback = (err, { key, ...info }) => {}) => stream

Store a mutable value in the DHT.

Options:

• keypair – REQUIRED, use node.mutable.keypair to generate this.
• signature - OPTIONAL, a buffer holding an ed25519 signature corresponding to public key. This can be supplied instead of a secret key which can be useful for offline signing. If signature is supplied keypair must only contain a publicKey and no secretKey. See signable and sign.
• seq - OPTIONAL - default 0, a number which should be increased every time put is passed a new value for the same keypair
• salt - OPTIONAL - default undefined, a buffer <= 64 bytes. If supplied it will salt the signature used to verify mutable values.

When successful the second argument passed to callback is an object containing the public key as key, with additional meta data (...info): signature, seq, salt.

node.mutable.get(key, [options], callback = (err, { value, ...info }) => {}) => stream

Fetch a mutable value from the DHT.

Options:

• seq - OPTIONAL, default 0, a number which will only return values with corresponding seq values that are greater than or equal to the supplied seq option.
• salt - OPTIONAL - default undefined, a buffer <= 64 bytes. If supplied it will salt the signature used to verify mutable values.

When successful, the second argument passed to callback is an object containing the resolved value with additional meta data (...info): signature, seq and salt.

Put / Get Stream Interface

All mutable and immutable Put / Get methods return a stream.

In addition to usual Node.js stream behaviour, the returned stream will emit warning events which may contain error information from other Nodes. The stream instance also has the following stat counters

• inflight - how many requests are currently active/ongoing
• responses - how many responses have been received
• errors - how many errors occurred (locally)
• updates - how many updates were made

node.on('listening')

Emitted when the node starts listening

node.on('close')

Emitted when the node is fully closed.

node.on('announce', topic, peer)

Emitted when an announce is received.

node.on('unannounce', topic, peer)

Emitted when an unannounce is received.

node.on('lookup', topic, peer)

Emitted when a lookup is received.

CLI

You can start a DHT node in the command line, using the @dswarm/cli package:

npm install -g @dswarm/cli
dswarm-dht # runs a DHT node

License

MIT