nkn-sdk-js

JavaScript implementation of NKN client and wallet SDK. The SDK consists of a few components:

• NKN Client: Send and receive data for free between any NKN clients regardless their network condition without setting up a server or relying on any third party services. Data are end to end encrypted by default. Typically you might want to use multiclient instead of using client directly.

• NKN MultiClient: Send and receive data using multiple NKN clients concurrently to improve reliability and latency. In addition, it supports session mode, a reliable streaming protocol similar to TCP based on ncp.

• NKN Wallet: Wallet SDK for NKN blockchain. It can be used to create wallet, transfer token to NKN wallet address, register name, subscribe to topic, etc.

Advantages of using NKN client/multiclient for data transmission:

• Network agnostic: Neither sender nor receiver needs to have public IP address or port forwarding. NKN clients only establish outbound (websocket) connections, so Internet access is all they need. This is ideal for client side peer to peer communication.

• Top level security: All data are end to end authenticated and encrypted. No one else in the world except sender and receiver can see or modify the content of the data. The same public key is used for both routing and encryption, eliminating the possibility of man in the middle attack.

• Decent performance: By aggregating multiple overlay paths concurrently, multiclient can get ~100ms end to end latency and 10+mbps end to end session throughput between international devices.

• Everything is free, open source and decentralized. (If you are curious, node relay traffic for clients for free to earn mining rewards in NKN blockchain.)

Documentation: https://docs.nkn.org/nkn-sdk-js.

Install

For npm:

npm install nkn-sdk

And then in your code:

const nkn = require('nkn-sdk');

or using ES6 import:

import nkn from 'nkn-sdk';

For browser, use dist/nkn.js or dist/nkn.min.js.

For environment where cryptographically secure random number generator is not natively implemented (e.g. React Native), see Random bytes generation.

Client

NKN client provides the basic functions of sending and receiving data between NKN clients or topics regardless their network condition without setting up a server or relying on any third party services. Typically you might want to use multiclient instead of using client directly.

Create a client with a generated key pair:

let client = new nkn.Client();

Or with an identifier (used to distinguish different clients sharing the same key pair):

let client = new nkn.Client({
  identifier: 'any-string',
});

Get client secret seed and public key:

console.log(client.getSeed(), client.getPublicKey());

Create a client using an existing secret seed:

let client = new nkn.Client({
  seed: '2bc5501d131696429264eb7286c44a29dd44dd66834d9471bd8b0eb875a1edb0',
});

Secret key should be kept SECRET! Never put it in version control system like here.

By default the client will use bootstrap RPC server (for getting node address) provided by nkn.org. Any NKN full node can serve as a bootstrap RPC server. You can create a client using customized bootstrap RPC server:

let client = new nkn.Client({
  rpcServerAddr: 'https://ip:port',
});

Get client NKN address, which is used to receive data from other clients:

console.log(client.addr);

Listen for connection established:

client.onConnect(() => {
  console.log('Client ready.');
});

Send text message to other clients:

client.send(
  'another-client-address',
  'hello world!',
);

You can also send byte array directly:

client.send(
  'another-client-address',
  Uint8Array.from([1,2,3,4,5]),
);

The destination address can also be a name registered using wallet.

Publish text message to all subscribers of a topic (subscribe is done through wallet):

client.publish(
  'topic',
  'hello world!',
);

Receive data from other clients:

client.onMessage(({ src, payload }) => {
  console.log('Receive message', payload, 'from', src);
});

If a valid data (string or Uint8Array) is returned at the end of the handler, the data will be sent back to sender as reply:

client.onMessage(({ src, payload }) => {
  return 'Well received!';
});

Handler can also be an async function, and reply can be byte array as well:

client.onMessage(async ({ src, payload }) => {
  return Uint8Array.from([1,2,3,4,5]);
});

Note that if multiple message handlers are added, the result returned by the first handler (in the order of being added) will be sent as reply.

The send method will return a Promise that will be resolved when sender receives a reply, or rejected if not receiving reply or acknowledgement within timeout period. Similar to message, reply can be either string or byte array:

client.send(
  'another-client-address',
  'hello world!',
).then((reply) => {
  // The reply here can be either string or Uint8Array
  console.log('Receive reply:', reply);
}).catch((e) => {
  // This will most likely to be timeout
  console.log('Catch:', e);
});

Client receiving data will automatically send an acknowledgement back to sender if message handler returns null or undefined so that sender will be able to know if the packet has been delivered. On the sender's side, it's almost the same as receiving a reply, except that the Promise is resolved with null:

client.send(
  'another-client-address',
  'hello world!',
).then(() => {
  console.log('Receive ACK');
}).catch((e) => {
  // This will most likely to be timeout
  console.log('Catch:', e);
});

If handler returns false, no reply or ACK will be sent.

Check examples/client.js for complete examples and https://docs.nkn.org/nkn-sdk-js for full documentation.

MultiClient

MultiClient creates multiple NKN client instances by adding identifier prefix (__0__., __1__., __2__., ...) to a NKN address and send/receive packets concurrently. This will greatly increase reliability and reduce latency at the cost of more bandwidth usage (proportional to the number of clients).

MultiClient basically has the same API as client, with a few additional initial configurations and session mode:

let multiclient = new nkn.MultiClient({
  numSubClients: 4,
  originalClient: false,
});

where originalClient controls whether a client with original identifier (without adding any additional identifier prefix) will be created, and numSubClients controls how many sub-clients to create by adding prefix __0__., __1__., __2__., etc. Using originalClient: true and numSubClients: 0 is equivalent to using a standard NKN Client without any modification to the identifier. Note that if you use originalClient: true and numSubClients is greater than 0, your identifier should not starts with __X__ where X is any number, otherwise you may end up with identifier collision.

Any additional options will be passed to NKN client.

MultiClient instance shares most of the public API as regular NKN client, see client for usage and examples. If you need low-level property or API, you can use multiclient.defaultClient to get the default client and multiclient.clients to get all clients.

Check examples/client.js for complete examples and https://docs.nkn.org/nkn-sdk-js for full documentation.

Session

In addition to the default packet mode, multiclient also supports session mode, a reliable streaming protocol similar to TCP based on ncp.

Listens for incoming sessions (without listen() no sessions will be accepted):

multiclient.listen();

Dial a session:

multiclient.dial('another-client-address').then((session) => {
  console.log(session.localAddr, 'dialed a session to', session.remoteAddr);
});

Accepts for incoming sessions:

multiclient.onSession((session) => {
  console.log(session.localAddr, 'accepted a session from', session.remoteAddr);
});

Write to session:

session.write(Uint8Array.from([1,2,3,4,5])).then(() => {
  console.log('write success');
});

Read from session:

session.read().then((data) => {
  console.log('read', data);
});

session.read also accepts a maxSize parameter, e.g. session.read(maxSize). If maxSize > 0, at most maxSize bytes will be returned. If maxSize == 0 or not set, the first batch of received data will be returned. If maxSize < 0, all received data will be concatenated and returned together.

Session can be converted to WebStream using session.getReadableStream() and session.getWritableStream(closeSessionOnEnd = false). Note that WebStream is not fully supported by all browser, so you might need to polyfill it globally or setting session.ReadableStream and session.WritableStream constructors.

Check examples/session.js for complete example or try demo file transfer web app at https://nftp.nkn.org and its source code at https://github.com/nknorg/nftp-js.

Wallet

NKN Wallet SDK.

Create a new wallet with a generated key pair:

let wallet = new nkn.Wallet({ password: 'password' });

Create wallet from a secret seed:

let wallet = new nkn.Wallet({
  seed: wallet.getSeed(),
  password: 'new-wallet-password',
});

Export wallet to JSON string:

let walletJson = wallet.toJSON();

Load wallet from JSON and password:

let wallet = nkn.Wallet.fromJSON(walletJson, { password: 'password' });

By default the wallet will use RPC server provided by nkn.org. Any NKN full node can serve as a RPC server. You can create a wallet using customized RPC server:

let wallet = new nkn.Wallet({
  password: 'password',
  rpcServerAddr: 'https://ip:port',
});

Verify whether an address is a valid NKN wallet address:

console.log(nkn.Wallet.verifyAddress(wallet.address));

Verify password of the wallet:

console.log(wallet.verifyPassword('password'));

Get balance of this wallet:

wallet.getBalance().then((value) => {
  console.log('Balance for this wallet is:', value.toString());
});

Transfer token to another wallet address:

wallet.transferTo(wallet.address, 1, { fee: 0.1, attrs: 'hello world' }).then((txnHash) => {
  console.log('Transfer transaction hash:', txnHash);
});

Subscribe to a topic for this wallet for next 100 blocks (around 20 seconds per block), client using the same key pair (seed) as this wallet and same identifier as passed to subscribe will be able to receive messages from this topic:

wallet.subscribe('topic', 100, 'identifier', 'metadata', { fee: '0.1' }).then((txnHash) => {
  console.log('Subscribe transaction hash:', txnHash);
});

Check examples/wallet.js for complete examples and https://docs.nkn.org/nkn-sdk-js for full documentation.

Random bytes generation

By default, this library uses the same random bytes generator as tweetnacl-js.

If a platform you are targeting doesn't implement secure random number generator, but you somehow have a cryptographically-strong source of entropy (not Math.random!), and you know what you are doing, you can plug it like this:

nkn.setPRNG(function(x, n) {
  // ... copy n random bytes into x ...
});

An example using node.js native crypto library:

crypto = require('crypto');
nkn.setPRNG(function(x, n) {
  var i, v = crypto.randomBytes(n);
  for (i = 0; i < n; i++) x[i] = v[i];
  // clean up v
});

Note that setPRNG completely replaces internal random byte generator with the one provided.

Contributing

Can I submit a bug, suggestion or feature request?

Yes. Please open an issue for that.

Can I contribute patches?

Yes, we appreciate your help! To make contributions, please fork the repo, push your changes to the forked repo with signed-off commits, and open a pull request here.

Please sign off your commit. This means adding a line "Signed-off-by: Name " at the end of each commit, indicating that you wrote the code and have the right to pass it on as an open source patch. This can be done automatically by adding -s when committing:

git commit -s

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