Multichain Quick Start - Plasma Bridge
Multichain Quick Start - Plasma Bridge
This page explains how to create an multi-chain indexer to index the bridge transfer that are coming from Polygon to Ethereum via the Polygon Plasma Bridge. After reading this guide, you'll understand how to match the events across several networks and learn how to set up a SubQuery indexer to monitor, track and aggregate those events from different EVM blockchains within a single entity.
There are two types of bridge on Polygon for asset transfer, the Proof of Stake (PoS) Bridge and the Plasma Bridge. The PoS Bridge, as the name suggests, adopts the Proof of Stake (PoS) consensus algorithm to secure its network. Deposits on the PoS Bridge are completed almost instantly, but withdrawals may take a while to confirm. On the other hand, the Plasma Bridge supports the transfer of Polygon's native token MATIC and certain Ethereum tokens (ETH, ERC-20, and ERC-721). It uses the Ethereum Plasma scaling solution to offer increased security.
Important
This project operates across multiple chains, making it more complex than other single chain examples.
Plasma bridge contracts have been deployed on both networks. In order to establish an indexer, we will need to asynchronously align the events from both of those smart contracts.
In the earlier Quickstart section , you should have taken note of three crucial files. To initiate the setup of a project from scratch, you can proceed to follow the steps outlined in the initialisation description.
As a prerequisite, you will need to generate types from the ABI files of each smart contract. Additionally, you can kickstart your project by using the EVM Scaffolding approach (detailed here). You'll find all the relevant events to be scaffolded in the documentation for each type of smart contract.
Note
Check the final code repository here to observe the integration of all previously mentioned configurations into a unified codebase.
Your Project Manifest File
The Project Manifest file is an entry point to your project. It defines most of the details on how SubQuery will index and transform the chain data.
The Multichain project contains multiple manifest files, with support for the following handlers:
- BlockHanders: On each and every block, run a mapping function
- TransactionHandlers: On each and every transaction that matches optional filter criteria, run a mapping function
- LogHanders: On each and every log that matches optional filter criteria, run a mapping function
dataSources:
- kind: ethereum/Runtime # We use ethereum runtime since Polygon is a layer-2 that is compatible
startBlock: 49174752
options:
# Must be a key of assets
abi: plasma
address: "0xd9c7c4ed4b66858301d0cb28cc88bf655fe34861" # Plasma contract
assets:
plasma:
file: "./abis/plasma.abi.json"
mapping:
file: "./dist/index.js"
handlers:
- handler: handlePolygonDeposit
kind: ethereum/LogHandler # We use ethereum handlers since Polygon is a layer-2 that is compatible
filter:
topics:
## Follows standard log filters https://docs.ethers.io/v5/concepts/events/
- TokenDeposited (address,address,address,uint256,uint256)
As you can see, we are only looking for a signle log - TokenDeposited. Data from this log will consequently be compared with the one emited in Ethereum network.
Note
Check out our Manifest File documentation to get more information about the Project Manifest (project.ts) file.
Next, change the name of the file mentioned above to polygon.yaml to indicate that this file holds the Ethereum configuration.
Then, create a multi-chain manifest file. After, following the steps outlined here, start adding the new networks. After you successfuly apply the correct entities for each chain, you will end up with a single subquery-multichain.yaml file that we'll map to the individual chain manifest files. This multi-chain manifest file will look something like this:
specVersion: 1.0.0
query:
name: "@subql/query"
version: "*"
projects:
- polygon.yaml
- ethereum.yaml
Now, we have to find the contract and the event on the Polygon network, which data will be matched with Ethereum's smart contract data. The manifest file for Polygon will have the following look:
dataSources:
- kind: ethereum/Runtime # We use ethereum runtime since Polygon is a layer-2 that is compatible
startBlock: 18434359
options:
# Must be a key of assets
abi: plasma-eth
address: "0x401F6c983eA34274ec46f84D70b31C151321188b"
assets:
plasma-eth:
file: "./abis/plasma-eth.abi.json"
mapping:
file: "./dist/index.js"
handlers:
- handler: handleEthereumDepositBlock
kind: ethereum/LogHandler # We use ethereum handlers since Polygon is a layer-2 that is compatible
filter:
topics:
## Follows standard log filters https://docs.ethers.io/v5/concepts/events/
- NewDepositBlock (address,address,uint256,uint256)
Here, again we are relying to the data of the single log, NewDepositBlock. Both logs will be processed asynchronously, without a specific order, and will be matched according to their data.
As evident from the examples above, we employ various handlers for different chains, while keeping the indexed event logs the same. This approach is adopted to facilitate the identification of the originating network for each specific event (refer to this tip). This strategy will prove beneficial later, as it allows us to incorporate a network field into the entities. This will simplify the execution of filtering, aggregation, and other data manipulation tasks.
Update Your GraphQL Schema File
The schema.graphql file determines the shape of your data from SubQuery due to the mechanism of the GraphQL query language. Hence, updating the GraphQL Schema file is the perfect place to start. It allows you to define your end goal right at the start.
From the aforementioned logs the following entities can be derived:
DepositOnPolygon: Represents deposits on the Polygon side of the bridge.DepositOnEthereum: Represents withdrawals (Ethereum deposits).BridgeTransaction: Connects Polygon deposits and Ethereum withdrawals.User: Represents user data, including wallet address and total deposits.
type DepositOnPolygon @entity {
id: ID! # Deposit Count Index
rootToken: String!
childToken: String!
user: User! # Foreign Key
amount: BigInt!
tx: String!
}
type DepositOnEthereum @entity {
id: ID! # Withdrawl Count Index
token: String!
user: User! # Foreign Key
amount: BigInt!
tx: String!
}
type BridgeTransaction @entity {
id: ID!
depositOnPolygon: DepositOnPolygon
depositOnEthereum: DepositOnEthereum
}
type User @entity {
id: ID! # Wallet Address
totalDeposits: BigInt!
}
These types help organise and query information about deposits, transactions, and users within SubQuery bridge indexer.
SubQuery simplifies and ensures type-safety when working with GraphQL entities, smart contracts, events, transactions, and logs. The SubQuery CLI will generate types based on your project's GraphQL schema and any contract ABIs included in the data sources.
yarn codegen
npm run-script codegen
This action will generate a new directory (or update the existing one) named src/types. Inside this directory, you will find automatically generated entity classes corresponding to each type defined in your schema.graphql. These classes facilitate type-safe operations for loading, reading, and writing entity fields. You can learn more about this process in the GraphQL Schema section.
It will also generate a class for every contract event, offering convenient access to event parameters, as well as information about the block and transaction from which the event originated. You can find detailed information on how this is achieved in the EVM Codegen from ABIs section. All of these types are stored in the src/types/abi-interfaces and src/types/contracts directories.
You can conveniently import all these types:
import {
DepositOnEthereum,
User,
DepositOnPolygon,
BridgeTransaction,
} from "../types";
import { TokenDepositedLog } from "../types/abi-interfaces/PlasmaAbi";
import { NewDepositBlockLog } from "../types/abi-interfaces/PlasmaEthAbi";
Add a Mapping Function
Mapping functions define how blockchain data is transformed into the optimised GraphQL entities that we previously defined in the schema.graphql file.
Note
Check out our Manifest File documentation to get more information about the Project Manifest (project.ts) file.
Navigate to the default mapping function in the src/mappings directory. Setting up mappings for this the Cosmos chains is straightforward. In this instance, the mappings are stored within the src/mappings directory, with the sole mapping file being mappingHandlers.ts. Now, let's take a closer look at it:
Setting up mappings for this smart contract is straightforward. In this instance, the mappings are stored within the src/mappings directory, with the sole mapping file being mappingHandlers.ts. Now, let's take a closer look at it:
import assert from "assert";
import {
DepositOnEthereum,
User,
DepositOnPolygon,
BridgeTransaction,
} from "../types";
import { TokenDepositedLog } from "../types/abi-interfaces/PlasmaAbi";
import { NewDepositBlockLog } from "../types/abi-interfaces/PlasmaEthAbi";
async function checkGetUser(user: string): Promise<User> {
let userRecord = await User.get(user.toLowerCase());
if (!userRecord) {
userRecord = User.create({
id: user.toLowerCase(),
totalDeposits: BigInt(0),
});
await userRecord.save();
}
return userRecord;
}
export async function handlePolygonDeposit(
deposit: TokenDepositedLog,
): Promise<void> {
assert(deposit.args, "No args on deposit");
const userId = deposit.args[2].toLowerCase();
const userRecord = await checkGetUser(userId);
const depositRecord = DepositOnPolygon.create({
id: deposit.args[4].toString(),
rootToken: deposit.args[0],
childToken: deposit.args[1],
userId: userId,
amount: deposit.args[3].toBigInt(),
tx: deposit.transactionHash,
});
await depositRecord.save();
userRecord.totalDeposits += depositRecord.amount;
await userRecord.save();
let bridgeTransactionRecord = await BridgeTransaction.get(
deposit.args.depositCount.toString(),
);
if (!bridgeTransactionRecord) {
bridgeTransactionRecord = BridgeTransaction.create({
id: deposit.args.depositCount.toString(),
});
}
bridgeTransactionRecord.depositOnPolygonId =
deposit.args.depositCount.toString();
await bridgeTransactionRecord.save();
}
export async function handleEthereumDepositBlock(
deposit: NewDepositBlockLog,
): Promise<void> {
assert(deposit.args, "No args on deposit");
const userId = deposit.args.owner.toLocaleLowerCase();
const userRecord = await checkGetUser(userId);
const depositRecord = DepositOnEthereum.create({
id: deposit.args.depositBlockId.toString(),
token: deposit.args.token,
userId: userId,
amount: deposit.args.amountOrNFTId.toBigInt(),
tx: deposit.transactionHash,
});
await depositRecord.save();
userRecord.totalDeposits += depositRecord.amount;
await userRecord.save();
let bridgeTransactionRecord = await BridgeTransaction.get(
deposit.args.depositBlockId.toString(),
);
if (!bridgeTransactionRecord) {
bridgeTransactionRecord = BridgeTransaction.create({
id: deposit.args.depositBlockId.toString(),
});
}
bridgeTransactionRecord.depositOnEthereumId =
deposit.args.depositBlockId.toString();
await bridgeTransactionRecord.save();
}
Here's a brief explanation of what this code does. There are two main functions defined:
handlePolygonDeposit: This function processes deposits made on the Polygon side of the bridge. It does the following:- Checks if the deposit log contains arguments.
- Retrieves or creates a user record using
checkGetUser. - Creates a deposit record for the Polygon deposit and saves it to the database.
- Updates the total deposits for the user.
- Creates or retrieves a bridge transaction record and associates it with the Polygon deposit.
handleEthereumDepositBlock: This function processes deposit blocks on the Ethereum side of the bridge. It performs similar actions ashandlePolygonDepositbut for Ethereum deposits.
The checkGetUser function is defined to retrieve a user's record from a database. If the user record doesn't exist, it creates one with an initial total deposit value of 0.
🎉 At this stage, we have successfully incorporated all the desired entities that can be retrieved from Plasma Bridge smart contracts. Additionally, we've created mapping handlers is designed to handle and store deposit-related information from both sides of the bridge, update user records, and maintain transaction records for deposits.
Note
Check the final code repository here to observe the integration of all previously mentioned configurations into a unified codebase.
Build Your Project
Next, build your work to run your new SubQuery project. Run the build command from the project's root directory as given here:
yarn build
npm run-script build
Important
Whenever you make changes to your mapping functions, you must rebuild your project.
Now, you are ready to run your first SubQuery project. Let’s check out the process of running your project in detail.
Whenever you create a new SubQuery Project, first, you must run it locally on your computer and test it and using Docker is the easiest and quickiest way to do this.
Run Your Project Locally with Docker
The docker-compose.yml file defines all the configurations that control how a SubQuery node runs. For a new project, which you have just initialised, you won't need to change anything.
However, visit the Running SubQuery Locally to get more information on the file and the settings.
Run the following command under the project directory:
yarn start:docker
npm run-script start:docker
Note
It may take a few minutes to download the required images and start the various nodes and Postgres databases.
Query your Project
Next, let's query our project. Follow these three simple steps to query your SubQuery project:
Open your browser and head to
http://localhost:3000.You will see a GraphQL playground in the browser and the schemas which are ready to query.
Find the Docs tab on the right side of the playground which should open a documentation drawer. This documentation is automatically generated and it helps you find what entities and methods you can query.
Try the following queries to understand how it works for your new SubQuery starter project. Don’t forget to learn more about the GraphQL Query language.
Bridge Transactions
Request
{
query {
bridgeTransactions {
nodes {
id
depositOnEthereum {
id
user {
id
}
token
amount
tx
}
depositOnPolygon {
id
user {
id
}
rootToken
amount
tx
}
}
}
}
}
Response
{
"data": {
"query": {
"bridgeTransactions": {
"nodes": [
{
"id": "529040001",
"depositOnEthereum": {
"id": "529040001",
"user": {
"id": "0xc163034e49f0ee158de7dd0aa37e665d560de40f"
},
"token": "0x7D1AfA7B718fb893dB30A3aBc0Cfc608AaCfeBB0",
"amount": "3113988835221724970000",
"tx": "0x8a082796ee2d846e3e064c34e08ae4510051896612e793f8e5b7a5314fcd1eb9"
},
"depositOnPolygon": {
"id": "529040001",
"user": {
"id": "0xc163034e49f0ee158de7dd0aa37e665d560de40f"
},
"token": "0x7D1AfA7B718fb893dB30A3aBc0Cfc608AaCfeBB0",
"amount": "3113988835221724970000",
"tx": "0x0b8a99dfea351f3f2dc7d8e114b2408df528660bfb9008d097c951fe87fa7a01"
}
}
]
}
}
}
}
Network Metadatas
Request
{
_metadatas {
totalCount
nodes {
chain
lastProcessedHeight
}
}
}
Response
{
"data": {
"_metadatas": {
"totalCount": 3,
"nodes": [
{
"chain": "137",
"lastProcessedHeight": 45222964
},
{
"chain": "1",
"lastProcessedHeight": 14312934
}
]
}
}
}
Note
Check the final code repository here.
What's next?
Congratulations! You have now a locally running SubQuery project that accepts GraphQL API requests for transferring data.
Tip
Find out how to build a performant SubQuery project and avoid common mistakes in Project Optimisation.
Click here to learn what should be your next step in your SubQuery journey.