# Architecture

How the API-key SDK layers ConnectRPC, realtime, catalogs, and services.

The SDK is a thin typed layer over two wire protocols:

- **ConnectRPC over HTTP** for unary requests (binary Protobuf by default)
- **Centrifugo over WebSocket** for realtime (binary Protobuf client protocol and payloads)

```text
Config / credentials          API URL, WS URL, Ed25519 key material, Account ID
        |
`polyester::Client`           wires transports, catalogs, and service accessors
  ├── Connect transport       public + authenticated unary calls
  ├── Realtime client         shared WebSocket multiplexer
  ├── Catalogs                spot + Zipper reference data / scales
  ├── Services                orders, market_data, balances, ...
  └── chain                   on-chain Funding helpers (not ConnectRPC)
```

Rust has **no** `candles` / `trading_withdraws` aliases. Use `market_data` and `withdraw`. Account resolve is out of scope for API-key SDKs.

Services are accessed as attributes/fields on the client (`client.orders`, `client.market_data`, …). Catalog hydration usually starts on client create; wait before decimal writes that depend on scales.

High-level service methods own authentication and request signing. The generated bindings under `polyester::connect` are deliberately low level and unsigned; use them only when you are prepared to implement the full wire contract yourself.

## Related

- [Environments](https://testnet.polyester.com/docs/sdk/rust/concepts/environments)
- [Client configuration](https://testnet.polyester.com/docs/sdk/rust/reference/client-configuration)
- [Realtime](https://testnet.polyester.com/docs/sdk/rust/reference/realtime)