@substrate/light-client-extension-helpers

@substrate/light-client-extension-helpers

Components

• backgroundHelper: Manages the core logic running in the background, including Smoldot instance registration, chain synchronization, active connections, and communication with the content script.
• contentScriptHelper: Handles communication between the tab's webpage and the extension's background script.
• webPageHelper: Provides an interface for the tab’s webpage to interact with the extension.
• extensionPagesHelper: A set of functions to manage persisted chains, connections, and boot-nodes within the extension page.
• smoldot: A thin abstraction over smoldot package that includes a restart method for the smoldot client

Example Usage

backgroundHelper

The module exposes a register function that is meant to be called in your background script. It does all the heavy lifting to manage your extension's connection to smoldot.

How You Can Use It

import { register } from "@substrate/light-client-extension-helpers/background"

const { lightClientPageHelper, addOnAddChainByUserListener } = register({
  smoldotClient: start({ maxLogLevel: 4 }),
  getWellKnownChainSpecs: () =>
    // these well known chains will be connected to when the extension is
    // started and their connection will always be maintained. The location
    // of these chainspecs is relative to your `assets` directory.
    Promise.all(
      [
        "./chainspecs/polkadot.json",
        "./chainspecs/ksmcc3.json",
        "./chainspecs/westend2.json",
      ].map((path) =>
        fetch(chrome.runtime.getURL(path)).then((response) => response.text()),
      ),
    ),
})

addOnAddChainByUserListener(async (inputChain) => {
  // listen for chain updates
})

contentScriptHelper

This module exposes a register function that should be called in your content script. Once registered you can access the light client provider in your inpage script.

This is useful if you are implementing the @substrate/discovery protocol

How You Can Use It

// constants.ts
export const CHANNEL_ID = "substrate-wallet-template"

// content/index.ts
import { register } from "@substrate/light-client-extension-helpers/content-script"
import { CHANNEL_ID } from "../constants"

register(CHANNEL_ID)

// inpage/index.ts
const provider = getLightClientProvider(CHANNEL_ID)

webPageHelper

The webpage helper allows any dapp to discover the light client provider that was registered using the contentScriptHelper. However this functionality has been superseded by the discovery protocol.

How You Can Use It

// use-provider.ts
import {
  type LightClientProvider,
  getLightClientProvider,
} from "@substrate/light-client-extension-helpers/web-page"
import { useEffect, useState } from "react"
import { useIsMounted } from "./useIsMounted"

const providers = new Map<string, Promise<LightClientProvider>>()

export const useLightClientProvider = (channelId: string) => {
  const [provider, setProvider] = useState<LightClientProvider>()
  const isMounted = useIsMounted()

  useEffect(() => {
    if (!providers.has(channelId))
      providers.set(channelId, getLightClientProvider(channelId))
    providers.get(channelId)?.then((provider) => {
      if (!isMounted()) return
      setProvider(provider)
    })
  }, [channelId, isMounted])

  return { provider }
}

extensionPagesHelper

The extension page helper is conceptually the same as the web page helper, except it is used in the user interface of your extension. By importing helper, you can access light client functionality.

How You Can Use It

Get and set the bootnodes

const getBootNodes = async (chainId: string) =>
  (await helper.getChains()).find(
    ({ genesisHash }) => genesisHash === wellKnownGenesisHashByChainId[chainId],
  )?.bootNodes ?? []

const setBootNodes = async (chainId: string, bootNodes: string[]) =>
  helper.setBootNodes(wellKnownGenesisHashByChainId[chainId], bootNodes)

Decode call data

import { getObservableClient } from "@polkadot-api/observable-client"
import { getViewBuilder } from "@polkadot-api/view-builder"
import { createClient } from "@polkadot-api/substrate-client"
import { helper } from "@substrate/light-client-extension-helpers/extension-page"
import { filter, firstValueFrom } from "rxjs"

export const decodeCallData = async (chainId: string, callData: string) => {
  const chains = await helper.getChains()
  const chain = chains.find(({ genesisHash }) => genesisHash === chainId)
  if (!chain) throw new Error("unknown chain")
  const client = getObservableClient(createClient(chain.provider))
  const { metadata$, unfollow } = client.chainHead$()
  try {
    const metadata = await firstValueFrom(metadata$.pipe(filter(Boolean)))
    return getViewBuilder(metadata).callDecoder(callData)
  } finally {
    unfollow()
    client.destroy()
  }
}

smoldot

The smoldot package is a streamlined version of the original smoldot package. Here are the key differences:

1. Restarts

   The smoldot client now includes a restart method. This is useful for restarting smoldot if it unexpectedly crashes, allowing you to quickly fire up a new instance.

2. Modified Add Chain Options

   When smoldot restarts, all prior connections made with client.addChain are lost. To address this, the AddChainOptions has been modified. The potentialRelayChains parameter is now a recursive AddChainOptions array instead of a Chain array. This ensures that when smoldot restarts and you need to call addChain to reconnect a parachain, the associated relaychain is always reconnected first.

3. Supervision

   This module also provides a supervise method, which checks the health of smoldot and automatically invokes the restart method if it detects an issue. It does this by repeatedly calling addChain with an empty string as the chainspec parameter. If addChain throws an error that isn't an AddChainError, it assumes smoldot is unhealthy and restarts it.

---

How You Can Use It

import { start } from "@substrate/light-client-extension-helpers/smoldot"

// Initialize the smoldot client
const client = start()

// Add a chain
client.addChain({
  chainSpec: "...",
  potentialRelayChains: [
    {
      chainSpec: "...",
      potentialRelayChains: [], // Recursive AddChainOptions array
    },
  ],
})

supervise(client, { onError: console.error })

// Supervise the client
client.supervise()