EVM Prediction Market Backend

Node.js TypeScript service for a prediction market on EVM chains: JSON-RPC reads/writes, REST API for a web UI, PostgreSQL via Prisma, an off-chain central limit order book (CLOB) with optional EIP-712 signed orders, and Socket.IO for live order book and trade updates.

This repository is a backend template. You must align the Solidity ABI (src/contracts/prediction-market.abi.ts) and environment variables with your deployed contracts.

Architecture

• Chain layer (src/services/blockchain/): ethers v6 JsonRpcProvider, read-only + optional operator wallet, calldata encoding for wallet-driven txs (/api/v1/tx/*), and a lightweight log listener that upserts Market rows and stores raw logs in ChainEvent.
• Order book (src/services/orderbook/): in-memory price–time priority matching per (marketId, outcomeIndex); PostgreSQL persists orders and trades. Suitable for a single API instance or a leader writer; for horizontal scale, add Redis or move matching behind a dedicated worker.
• UI integration: CORS-enabled REST + GET /api/v1/config/eip712 for typed-data signing; Socket.IO rooms market:<prismaMarketId> with events orderbook:updated and trade.

Prerequisites

• Node.js 20+
• PostgreSQL 14+

Setup

1. Copy .env.example to .env and set DATABASE_URL, RPC_URL, CHAIN_ID, PREDICTION_MARKET_ADDRESS, and EIP-712 fields to match your deployment and frontend.

2. Install dependencies and generate the Prisma client:

   npm install
   npx prisma generate
   npx prisma db push

3. Development:

   npm run dev

4. Production build:

   npm run build
   npm start

Environment

See .env.example for all variables. Important:

Variable	Role
DATABASE_URL	PostgreSQL connection string
RPC_URL	HTTPS JSON-RPC endpoint
CHAIN_ID	Must match the chain id returned by the RPC
PREDICTION_MARKET_ADDRESS	Core market contract
OPERATOR_PRIVATE_KEY	Optional; only if the server submits transactions
CORS_ORIGINS	Comma-separated browser origins
EIP712_*	Must match the values used by your web app when signing orders

HTTP API (summary)

Base path: API_PREFIX (default /api/v1).

Method	Path	Description
GET	/health	Liveness
GET	/api/v1/config/eip712	EIP-712 domain and types for order signing
GET	/api/v1/markets	List markets (`?resolved=true
POST	/api/v1/markets	Register/upsert a market row (or rely on indexer)
GET	/api/v1/markets/:id	Market by Prisma id
GET	/api/v1/markets/:id/chain	DB row + on-chain getMarket snapshot
GET	/api/v1/markets/:id/orderbook?outcomeIndex=0	Bids/asks snapshot
POST	/api/v1/markets/:id/orders	Place order (optional requireSignature: true)
GET	/api/v1/markets/:id/trades	Recent trades
DELETE	/api/v1/orders/:orderId?requester=0x…	Cancel resting order
GET	/api/v1/users/:address/orders	Orders for a wallet
POST	/api/v1/tx/buy	Unsigned buy calldata for the user wallet
POST	/api/v1/tx/sell	Unsigned sell calldata
POST	/api/v1/tx/claim	Unsigned claim calldata

Order placement body (example)

{
  "makerAddress": "0x…",
  "outcomeIndex": 0,
  "side": "BUY",
  "priceBps": 5500,
  "sizeRaw": "1000000",
  "requireSignature": false
}

priceBps is basis points of probability (1–10000). sizeRaw is an integer string in your collateral’s smallest units (convention must match the on-chain settlement path you implement).

With requireSignature: true, include signature and chainNonce matching GET /api/v1/config/eip712 and src/services/signing/eip712-order.ts.

Socket.IO (browser / UI)

connect → emit("market:subscribe", "<prismaMarketId>")
listen: "orderbook:updated" | "trade"

Smart contract alignment

1. Update src/contracts/prediction-market.abi.ts to match your contract.
2. Ensure events MarketCreated / MarketResolved match if you use event-indexer.service.ts.
3. Expose getMarket(bytes32) (or adjust prediction-market.chain.ts) so /markets/:id/chain stays accurate.

Contact Information

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