# Session 01: Foundation Types

## Summary

Constants, error types, error catalog, protocol definitions, ring buffer, rate counter, stream distribution model, and NKey utilities. These are the leaf types with no internal dependencies — everything else builds on them.

## Scope

| Go File | Features | Feature IDs | Go LOC |
|---------|----------|-------------|--------|
| server/const.go | 2 | 582–583 | 18 |
| server/errors.go | 15 | 833–847 | 92 |
| server/errors_gen.go | 6 | 848–853 | 158 |
| server/proto.go | 6 | 2593–2598 | 237 |
| server/ring.go | 6 | 2889–2894 | 34 |
| server/rate_counter.go | 3 | 2797–2799 | 34 |
| server/sdm.go | 5 | 2966–2970 | 39 |
| server/nkey.go | 3 | 2440–2442 | 14 |
| **Total** | **46** | | **626** |

## .NET Classes

- `Constants` — server constants and version info
- `ServerErrorCatalog` — generated error codes and messages
- `Protocol` — NATS protocol string constants
- `RingBuffer` — fixed-size circular buffer
- `RateCounter` — sliding window rate measurement
- `StreamDistributionModel` — stream distribution enum/types
- `NkeyUser` — NKey authentication types

## Test Files

| Test File | Tests | Test IDs |
|-----------|-------|----------|
| server/errors_test.go | 2 | 297–298 |
| server/ring_test.go | 2 | 2794–2795 |
| server/rate_counter_test.go | 1 | 2720 |
| server/nkey_test.go | 9 | 2362–2370 |
| server/trust_test.go | 3 | 3058–3060 |
| **Total** | **17** | |

## Dependencies

- None (leaf session)

## .NET Target Location

- `dotnet/src/ZB.MOM.NatsNet.Server/` — types and enums at root or `Internal/`