A library and commands to interact with RSK and Ethereum nodes

In recent years I have carried out various experiments with RSK blockchains nodes (local, testnet, mainnet) and also with local ganache, geth and parity nodes. The way to connect from an external application to those Ethereum nodes is using JSON RPC. Although there are several libraries (in JavaScript, Python and other languages) to send these messages, I preferred writing my own library to learn how the protocol works. As I try to pursue simplicity, I was not convinced to use libraries (like web3js) that seem too huge to me.

So I wrote RskAPI as a personal project. It is a JavaScript library that allows connecting to a node, using http or https as transport.

Keep it simple, and learn

As usual in my personal projects in JavaScript (and other languages) I add few dependencies. At the end term, all the interaction that I want is simply to send and receive JSON messages, nothing else. So, for many months, this project was growing only with other of my personal projects as dependencies (like simplejsonrpc).

One of the concessions that I had to make to my inclination to have few dependencies in this type of projects, was the need to include two libraries that allow me to sign and encode transactions, something very common with these nodes, where in production it is recommended not to have the private keys on the node itself, but sign the transactions from the external application. This is the main use case to have more dependencies in a project like this.

Using commands

You can use my library simply from plain JavaScript in node.js:

const rskapi = require('rskapi');
// Connecting to a local node, maybe RSK regtest
const client = rskapi.client('http://localhost:4444');
/** operations with the node **/
const number = await client.number(); // best block number
const bestBlock = await client.block(number); // retrieve best block

But I found very useful to have sample commands: Command-line programs that executes tasks, and save results in a configuration file. See samples/commands folder.

Let’s run an example. From this folder, execute:

node sethost https://public-node.testnet.rsk.co:443

This is the RSK public node for testnet (see RSK public nodes). In my library, you MUST specify the port (443) if you are using https transport.

You need an account. Create a random one and associate it with a logical name:

node genaccount root

The configuration file config.json have the data of the account. This approach is for experimental tasks, not for production. The generated public address is shown, then you could add funds using RSK testnet faucet.

You can retrieve the balance (in weis) using

node getbalance root

You can create new accounts with:

node genaccount alice
node genaccount bob
node genaccount charlie

You can transfer weis from one account to another:

node transfer root alice 1000000000000
node transfer root bob 1000000000000

Retrieve all the balance:

node getbalances

The sample also includes some smart contracts in contracts folder and their compilation result (using truffle) already available in build/contracts folder. So, without truffle, you even can deploy the contract, e.g. Counter, to an instance, using the funds of an account to pay the deployment:

node deploy root counter1 Counter

The name counter1 is the logical name of the new account just created with the deployed contract.

You can query the contract:

node call root counter1 counter()

and invoke it to change its status

node invoke root counter1 increment()
node invoke root counter1 increment()
node invoke root counter1 add(uint256) 40
node call root counter1 counter()

I’m using some older versions of these commands and library in others of my projects, like RskUtils, EthMeta and DeFiProt.

Other available objects

There are other objects that can be use from the library. One is the host: A client is only a wrapper of a host, that it is in charge of some formatting and validations, not to be discussed here (I’m thinking of some internal refactors).

You can get an host in two ways:

// from a client
const client = rskapi.client('http://localhost:4444');
const host = client.host();
// or directly
const host = rskapi.host('http://localhost:4444');

If you need to invoke a particular JSON RPC method not directly supported by a client or host, you can use the provider object:

const provider = host.provider();
// I should add too client.provider()

that is an instance of simplejsonrpc project.

Future work

I will add some additional functions to clients, like log retrieval and code retrieval. I plan to add the commands too. And I will add some programming examples, with more intensive tasks, like sending many transactions from differents accounts, deploying and invoking tokens, etc.

I’m having fun :-)