Blockchain Price Oracle

Real-time cryptocurrency price oracle

What it does

1. Historical sync - backfills price history from contract deployment block up to the current state
2. Fetches BTC/ETH/LINK prices from CoinGecko every minute
3. Updates smart contract when price differs >2% from on-chain AND <20% from Chainlink
4. Streams contract price changes (all sources) via WebSocket
5. Serves current prices, time-range history, history of reverts
6. Zero reverts - prevents gas waste by pre-TX validation and by waiting previously sent TX for chosen symbol to be completed
7. Multi-instance ready - easy to add distributed lock coordination to keep contract reverts at zero when multiple instances are running at the same time
8. Extensible - easy to add new symbols (BTC/ETH/LINK/...) when contract supports it
9. Rate limited RPC & API usage - protects external calls (CoinGecko, Ankr RPC..) from hitting provider limits
10. Isolated rate limits per usage - separate limiters for app production mode and sync process (supports different API keys)

Setup

Create .env file in root directory

ENV

ANKR_SEPOLIA_API_KEY=your_ankr_key
ANKR_SEPOLIA_SYNC_API_KEY=your_2_ankr_key
COINGECKO_API_KEY=your_coingecko_key
WSS_URL=wss://eth-sepolia.g.alchemy.com/v2/your_key
CONTRACT_ADDR=0x0A7cF8518Eca70cfe64Ff9B28Cb0D8162F31A41D
DEPLOYMENT_BLOCK=10588291
PRIVATE_KEY=0xabcdef...  # 64 hex chars (no 0x prefix)

Run

go mod tidy
go run app/main.go

Provided API Endpoints

Endpoint	Method	Description
/api/v1/prices/:symbol	GET	Current prices (on-chain+CL+CG)
/api/v1/prices/:symbol/last	GET	Last N prices (?n=10)
/api/v1/prices/:symbol/range	POST	Time range query for prices
/api/v1/reverts	GET	Revert history (?n=100)
/api/v1/health	GET	Server status

Tech Stack

• Go 1.25.0
• Gin
• Ethereum Sepolia
• Solidity ^0.8.20
• go-ethereum
• Alchemy WSS
• WebSockets streaming
• Ankr Sepolia
• CoinGecko API
• Chainlink Price Feeds
• Storage: In-memory FIFO
• Rate Limiting
• Concurrency
• Testing (mocks / dependency injection)