@dfinity/agent

What is @dfinity/agent?

@dfinity/agent is a JavaScript library that allows developers to interact with the Internet Computer, a decentralized computing platform. It provides tools to create, manage, and communicate with canisters (smart contracts) on the Internet Computer.

What are @dfinity/agent's main functionalities?

Creating an HTTP Agent

This feature allows you to create an HTTP agent to communicate with the Internet Computer. The agent is configured with a host URL, which is the entry point to the network.

const { HttpAgent } = require('@dfinity/agent');
const agent = new HttpAgent({ host: 'https://ic0.app' });

Interacting with Canisters

This feature demonstrates how to interact with a canister using an actor. You define an interface for the canister and create an actor to call its methods, such as 'greet' in this example.

const { Actor, HttpAgent } = require('@dfinity/agent');
const agent = new HttpAgent();
const canisterId = 'your-canister-id';
const interfaceFactory = ({ IDL }) => IDL.Service({
  greet: IDL.Func([IDL.Text], [IDL.Text], []),
});
const actor = Actor.createActor(interfaceFactory, { agent, canisterId });
const response = await actor.greet('World');

Querying and Updating Canister State

This feature shows how to query and update the state of a canister. The 'getValue' method is a query call, while 'setValue' is an update call, demonstrating both read and write operations.

const { Actor, HttpAgent } = require('@dfinity/agent');
const agent = new HttpAgent();
const canisterId = 'your-canister-id';
const interfaceFactory = ({ IDL }) => IDL.Service({
  getValue: IDL.Func([], [IDL.Nat], ['query']),
  setValue: IDL.Func([IDL.Nat], [], []),
});
const actor = Actor.createActor(interfaceFactory, { agent, canisterId });
const currentValue = await actor.getValue();
await actor.setValue(currentValue + 1);

Other packages similar to @dfinity/agent

ethers

Ethers.js is a library for interacting with the Ethereum blockchain. Like @dfinity/agent, it provides tools for creating and managing connections to a decentralized network, but it is specific to Ethereum rather than the Internet Computer.

web3

Web3.js is another library for interacting with the Ethereum blockchain. It offers similar functionalities to @dfinity/agent, such as sending transactions and interacting with smart contracts, but it is tailored for Ethereum.

near-api-js

Near-api-js is a JavaScript library for interacting with the NEAR blockchain. It provides similar functionalities to @dfinity/agent, such as managing accounts and interacting with smart contracts, but it is designed for the NEAR protocol.

README

@dfinity/agent

JavaScript and TypeScript library to interact with the Internet Computer for Node.js and browser applications.

Do you want to know more about developing on the Internet Computer? Visit the Developer Docs.

Additional API Documentation can be found here.

Installation

Using agent:

npm i --save @dfinity/agent

In the browser:

import * as agent from '@dfinity/agent';

or using individual exports:

import { Actor, HttpAgent } from '@dfinity/agent';

In Node.js

const DfinityAgent = require('@dfinity/agent');

or using individual exports:

const { Actor, HttpAgent } = require('@dfinity/agent');

Using an Agent

The agent is a low-level interface that the Actor uses to encode and decode messages to the Internet Computer. It provides call, query and readState methods to the Actor, as well as a few additional utilities. For the most part, calls through the agent are intended to be structured through an Actor, configured with a canister interface that can be automatically generated from a Candid interface.

Initializing an Actor

The most common use for the agent is to create an actor. This is done by calling the Actor.createActor constructor:

Actor.createActor(interfaceFactory: InterfaceFactory, configuration: ActorConfig): ActorSubclass<T>

The interfaceFactory is a function that returns a runtime interface that the Actor uses to strucure calls to a canister. The interfaceFactory can be written manually, but it is recommended to use the dfx generate command to generate the interface for your project, or to use the didc tool to generate the interface for your project.

Actors can also be initialized to include the boundary node http headers, This is done by calling the Actor.createActor constructor:

Actor.createActorWithHttpDetails(interfaceFactory: InterfaceFactory, configuration: ActorConfig): ActorSubclass<ActorMethodMappedWithHttpDetails<T>>

Inspecting an actor's agent

Use the Actor.agentOf method to get the agent of an actor:

const defaultAgent = Actor.agentOf(defaultActor);

This is useful if you need to replace or invalidate the identity used by an actor's agent.

For example, if you want to replace the identity of an actor's agent with a newly authenticated identity from Internet Identity, you can do so by calling the Actor.replaceAgent method:

defaultAgent.replaceIdentity(await authClient.getIdentity());

Tips for using fetch

The agent uses the browser fetch API to make calls to the Internet Computer. If you are not using the agent in the browser, you can pass a custom fetch implementation to the agent's constructor. This is useful if you want to use a custom fetch implementation, such as one that adds authentication headers to the request. We recommend using the isomorphic-fetch package to provide a consistent fetch API across Node.js and the browser. You will also need to provide a host option to the agent's constructor, as the agent will not be able to determine the host from the global context.

For example,

import fetch from 'isomorphic-fetch';
import { HttpAgent } from '@dfinity/agent';

const host = process.env.DFX_NETWORK === 'local' ? 'http://127.0.0.1:4943' : 'https://icp-api.io';

const agent = new HttpAgent({ fetch, host });

You can also pass fetchOptions to the agent's constructor, which will be passed to the fetch implementation. This is useful if you want to pass additional options to the fetch implementation, such as a custom header.

For example,

import fetch from 'isomorphic-fetch';
import { HttpAgent } from '@dfinity/agent';

const host = process.env.DFX_NETWORK === 'local' ? 'http://127.0.0.1:4943' : 'https://ic0.app';

/**
 * @type {RequestInit}
 */
const fetchOptions = {
  headers: {
    'X-Custom-Header': 'value',
  },
};

const agent = new HttpAgent({ fetch, host, fetchOptions });