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Add custom RPC methods

Introduction​

Web3.js is a popular library for interacting with the Ethereum blockchain. It provides a set of APIs to interact with Ethereum nodes via JSON-RPC calls. For adding new JSON-RPC function calls to the library, you can do so using the plugin feature in web3.js 4.x. This allows you to extend the functionality of Web3.js and add support for new JSON-RPC methods.

caution

In Web3.js 1.x, web3.extend() function could be used to add new JSON-RPC methods. web3.extend() is also available in Web3 v4.0.4+ with some breaking changes. However it is recommended to use Web3 Plugin feature for extending web3 functionality if you are developing new feature.

Following tutorial will guide you through the process of creating a custom plugin to extend the functionality of web3.js 4.x and add support for new RPC methods.

Creating new RPC methods Plugin in 4 Steps​

Step 1: Setting Up Web3.js as a Peer Dependency and Creating a TypeScript Class​

  1. First add web3.js as peer dependency in project´s package.json and create a TypeScript class for your plugin. This class should extend the Web3Plugin class provided by web3.js.
info

This will give your plugin access to requestManager and accountProvider.

import { Web3PluginBase } from 'web3';

export default class CustomRpcMethodsPlugin extends Web3PluginBase {
  // step 1
  // ...
}

Step 2: Adding a Public pluginNamespace Property to the Plugin Class​

  1. After that add public pluginNamespace property. This will be used to access your plugin, as mentioned in step number 5 code example.
import { Web3PluginBase } from 'web3';

export default class CustomRpcMethodsPlugin extends Web3PluginBase {
  public pluginNamespace = 'customRpcMethods'; // step 2
}

Step 3: Creating Custom RPC Methods in the Plugin Class​

  1. Once plugin class is created using above mentioned steps, its very easy to add new RPC methods like:
import { Web3PluginBase } from 'web3';

export default class CustomRpcMethodsPlugin extends Web3PluginBase {
  public pluginNamespace = 'customRpcMethods';

  public async customRpcMethod() {
    // step 3
    return this.requestManager.send({
      // plugin has access to web3.js internal features like request manager
      method: 'custom_rpc_method',
      params: [],
    });
  }
}

Step 4: Enabling Access to the Plugin on the Web3 Object​

  1. (For TypeScript) Final step is setting up module augmentation, this will allow you to access plugin on web3 object.
import { Web3PluginBase } from 'web3';

export default class CustomRpcMethodsPlugin extends Web3PluginBase {
  public pluginNamespace = 'customRpcMethods';

  public async customRpcMethod() {
    return this.requestManager.send({
      // plugin has access to web3.js internal features like request manager
      method: 'custom_rpc_method',
      params: [],
    });
  }
}

// Module Augmentation
declare module 'web3' {
  // step 4

  interface Web3Context {
    customRpcMethods: CustomRpcMethodsPlugin;
  }
}
info

After the plugin is ready, it is recommended to publish it on the NPM registry.

Step 5: Using the Web3 CustomRPCPlugin with a Web3 Instance​

  1. First add plugin in your plugin consumer project's package.json, create web3 and plugin instances, and after that use .registerPlugin method with some web3.js module (in following example its registered with main web3).

Once plugin is registered its custom methods will be available to use.

import { Web3 } from 'web3';
import CustomRpcMethodsPlugin from 'web3-plugin-example';

const web3 = new Web3('http://127.0.0.1:8545');

web3.registerPlugin(new CustomRpcMethodsPlugin()); // step 5

web3.customRpcMethods.customRpcMethod(); //usage

More Details of Plugin Feature​

For more details follow :