Offchain Café: EVM

A simple-to-use EVM chain indexing made for Web3 applications.

Features

• Synchronize contract logs
• Serve the logs via GraphQL, including realtime subscriptions

Usage

To run Offchain Café: EVM, you'll need the following:

• A PostgreSQL database (DATABASE_URL)
• A Redis instance (REDIS_URL)
• An Ethereum RPC endpoint (ETH_CHAIN_ID, ETH_HTTP_RPC_URL and ETH_WS_RPC_URL (optional, but recommended))
• Addresses and deploy block numbers of the contracts you want to index

1. Prepare contracts.json (see contracts.example.json for an example)
2. Prepare environment (see env.example for an example)
3. Run pnpm install && pnpm build
4. Run pnpm db:migrate to create the database schema
5. Run pnpm start

You should now have the GraphQL API endpoint running at /graphql. Enjoy! ☕️

Client examples

This example uses @urql/core in NodeJS environment.

offchainCafe.ts

import{createClient,defaultExchanges}from"@urql/core";import{yogaExchange}from"@graphql-yoga/urql-exchange";constclient=createClient({url: "http://<OFFCHAIN_SERVER_HOST>:<OFFCHAIN_SERVER_PORT>/graphql",exchanges: [...defaultExchanges,yogaExchange()],});exportdefaultclient;

queryLogs.ts

import{gql}from"@urql/core";importoffchainCafefrom"./offchainCafe";importreceiverAbifrom"~/abi/receiver.json" assert {type: "json"};constreceiverAddress="0x...";constiface=newethers.utils.Interface(receiverAbi);constreceiveEventTopic=iface.getEventTopic("Receive");constfromBlock=0;// 0 means contract creation blockconsttoBlock=-1;// -1 means the latest chain blockconstlogs=(awaitoffchainCafe.query(gql` query ContractLogs( $fromBlock: Int!, $toBlock: Int! ) { contract(address: "${receiverAddress}") { logs( topics: [["${receiveEventTopic}"]], limit: 10, fromBlock: $fromBlock, toBlock: $toBlock ) { block { number timestamp } logIndex transaction { hash } data topics } } }`,{ fromBlock, toBlock }).toPromise()).data.contract.logs;

subscribeToLogs.ts

import{pipe,subscribe}from"wonka";import{gql}from"@urql/core";importoffchainCafefrom"./offchainCafe";importreceiverAbifrom"~/abi/receiver.json" assert {type: "json"};constreceiverAddress="0x...";constiface=newethers.utils.Interface(receiverAbi);constreceiveEventTopic=iface.getEventTopic("Receive");const{ unsubscribe }=pipe(offchainCafe.subscription(gql` subscription { log( contractAddress: "${receiverAddress}", topics: [["${receiveEventTopic}"]] ) { block { number timestamp } logIndex transaction { hash } data topics } }`,{}),subscribe(async(result)=>{constlog=result.data!.log;}));