dApp Server

A lightweight and flexible indexer for EVM smart contracts, connecting a couple of popular libraries to provide a simple self-hosted indexing solution.

Ethers is used to listen to contract events. Redis is used to store data. Express serves the data. GraphQL is supported but optional.

	dApp Server	The Graph
decentralized data-integrity	-	✓
distributed/redundant storage	✓	✓
self-hosted/self-owned	✓	run an indexer (requires GRT)
number of listeners	depends on you (only)	pretty much unlimited
contract factory support	✓	✓
GraphQL support	✓	✓
REST support	✓	-
freely design API endpoints	✓	-
index arbitrary data / call APIs	✓	-
POST/Mutation support	✓	-
optional/custom billing	✓	-
package size	22 kB so far (npm package)	563 kB cli tool, 335 MB node
cognitive load	you might know already	another docs bookmark
Tech	Javascript	AssemblyScript, WASM, Rust

Usage

1npm i @mktcodelib/web3indexer

1// indexer.js
2import { Web3Indexer } from '@mktcodelib/web3indexer';
3import { TransferListener } from './listeners/Transfer';
4import { TransfersEndpoint } from './endpoints/transfers';
5import { schema } from './graphql/schema';
6import { resolvers } from './graphql/resolvers';
7import CONTRACT from './listeners/CONTRACT.json';
8
9if (!process.env.PROVIDER_URL) throw new Error('PROVIDER_URL env variable is required');
10
11const indexer = new Web3Indexer({ provider: process.env.PROVIDER_URL });
12
13const contract = indexer.contract(CONTRACT.address, CONTRACT.abi)
14contract.store("Transfer", TransferListener);
15
16indexer.api.get('/transfers', TransfersEndpoint);
17indexer.api.graphql(schema, resolvers);
18
19indexer.replay();

1// listeners/Transfer.js
2export function TransferListener(db) {
3  return async (from, to, tokenId, event) => {
4    db.hSet("Transfer", event.transactionHash, JSON.stringify({ from, to, tokenId: tokenId.toString() }));
5  }
6}

1// endpoints/transfers.js
2export function TransfersEndpoint(db) {
3  return async (req, res) => {
4    const cached = await db.hGetAll('Transfer');
5  
6    if (cached) {
7      Object.keys(cached).forEach((key) => {
8        cached[key] = JSON.parse(cached[key]!);
9      });
10    }
11  
12    res.send(cached || {});
13  }
14}

1// graphql/schema.js
2import { buildASTSchema } from "graphql";
3import gql from "graphql-tag";
4
5const ast = gql`
6type Transfer {
7  from: String
8  to: String
9  tokenId: String
10}
11
12type Query {
13  transfers: [Transfer!]
14}
15`;
16
17export const schema = buildASTSchema(ast);

1// graphql/resolvers.js
2export function resolvers(db) {
3  return {
4    transfers: async () => {
5      const cached = await db.hGetAll("Transfer");
6      
7      if (!cached) return [];
8      
9      return Object.keys(cached).map((key) => JSON.parse(cached[key]!));
10    },
11  }
12};

1$ node indexer.js
2
3Listening on http://localhost:3000
4
5Routes:
6GET /events/transfers

Docker

You can start with this templpate repository and adjust it to your needs.