Minimal CEX-like Deposits, Indexing, and API

A small, focused project that issues per-user deposit addresses, indexes on-chain activity, and exposes simple APIs your frontend can use to behave like a lightweight CEX.

What this repo contains

• BE: Express + MongoDB API for signup/auth and getting deposit addresses.
• Indexer: EVM block listener (ethers v6) + Redis + MongoDB. Tracks deposits for “interested addresses” and updates user balances.

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Architecture

            ┌──────────────────────────────────┐
            │            Frontend              │
            │  (login, show address, balance) │
            └───────────────┬──────────────────┘
                            │ REST
                            ▼
                    ┌──────────────┐
                    │     BE       │
                    │  Express API │
                    └──────┬───────┘
                           │ Mongo (Users)
                           ▼
                     ┌────────────┐
                     │  MongoDB   │
                     └────────────┘
                           ▲
                           │ writes (balances)
   Redis (checkpoint, addr cache)  │
         ┌──────────────────┐      │
         │      Redis       │◄─────┘
         └────────┬─────────┘
                  │
                  ▼
           ┌──────────────┐    EVM RPC
           │   Indexer    │────────────► Provider
           │  (ethers v6) │    (Sepolia/Mainnet)
           └──────────────┘

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How the Indexer works (high-level)

1. Load "interested addresses" (deposit addresses) from MongoDB. Cache them in Redis.
2. Read last processed block from Redis (checkpoint). If none, start at current head.
3. On each new block:
   • Fetch full transactions for that block in one call.
   • Filter txs where from or to matches an interested address (normalized lowercase).
   • For each relevant address: fetch balance via provider and upsert to Mongo; also cache results in Redis.
   • Save the processed block number back to Redis.

Key modules (Indexer)

• src/config/block.ts
  • processBlock(blockNumber, addresses) – fetch block with full transactions (1 RPC), filter for relevant addresses, update balances.
  • startBlockListener(addresses) – subscribe to new blocks, process sequentially with catch-up logging, save checkpoints.
• src/services/addresses.ts
  • LoadInteresetdAddresses() – load deposit addresses from Mongo, normalize to lowercase, cache in Redis.
• src/services/bloclService.ts
  • getLastProcessedblock() / setLastProcessedBlock(n) – checkpoint helpers stored in Redis.
• src/services/Updatedb.ts
  • check_balance_update_db(address) – get on-chain balance, compare with DB, update if changed, cache in Redis.

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Backend (BE) – Routes & behavior

• POST /api/auth/signup
  • Creates a new user: derives a unique deposit address (HD path), stores email, DepositAddress, userId, privateKey, and initial balance.
  • Invalidates Redis key interested_addresses so the indexer reloads the new address.
• GET /api/getAddress
  • Returns the user's deposit address (implementation lives under routes/DepositAddress).
• GET /health
  • Liveness endpoint.

Environment

Create .env files for BE and Indexer with at least:

ETH_RPC_URL=...          # e.g., https://sepolia.infura.io/v3/<key>
MONGO_DB_CONNECTION=...  # e.g., mongodb://localhost:27017/stake
REDIS_URL=redis://localhost:6379
PORT=5000                # for BE

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Running locally

1. Infra (one-time):

docker run -d --name mongo -p 27017:27017 mongo:7
docker run -d --name redis -p 6379:6379 redis:7

2. Backend:

cd BE
npm i
npm run dev

3. Indexer:

cd indexer
npm i
npm run dev

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