natsdotnet/Documentation/Operations/Overview.md

# Operations Overview

This document covers running the server, graceful shutdown, connecting clients, and the test suite.

---

## Running the Server

The host application is `src/NATS.Server.Host`. Run it with `dotnet run`:

```bash
# Default (port 4222, bind 0.0.0.0)
dotnet run --project src/NATS.Server.Host

# Custom port
dotnet run --project src/NATS.Server.Host -- -p 14222

# Custom bind address and name
dotnet run --project src/NATS.Server.Host -- -a 127.0.0.1 -n my-server
```

Arguments after `--` are passed to the program. The three supported flags are `-p`/`--port`, `-a`/`--addr`, and `-n`/`--name`. See [Configuration Overview](../Configuration/Overview.md) for the full CLI reference.

On startup, the server logs the address it is listening on:

```
[14:32:01 INF] Listening on 0.0.0.0:4222
```

### Full host setup

`Program.cs` initializes Serilog, parses CLI arguments, starts the server, and handles graceful shutdown:

```csharp
using NATS.Server;
using Serilog;

Log.Logger = new LoggerConfiguration()
    .MinimumLevel.Debug()
    .Enrich.FromLogContext()
    .WriteTo.Console(outputTemplate: "[{Timestamp:HH:mm:ss} {Level:u3}] {Message:lj}{NewLine}{Exception}")
    .CreateLogger();

var options = new NatsOptions();

for (int i = 0; i < args.Length; i++)
{
    switch (args[i])
    {
        case "-p" or "--port" when i + 1 < args.Length:
            options.Port = int.Parse(args[++i]);
            break;
        case "-a" or "--addr" when i + 1 < args.Length:
            options.Host = args[++i];
            break;
        case "-n" or "--name" when i + 1 < args.Length:
            options.ServerName = args[++i];
            break;
    }
}

using var loggerFactory = new Serilog.Extensions.Logging.SerilogLoggerFactory(Log.Logger);
var server = new NatsServer(options, loggerFactory);

var cts = new CancellationTokenSource();
Console.CancelKeyPress += (_, e) =>
{
    e.Cancel = true;
    cts.Cancel();
};

try
{
    await server.StartAsync(cts.Token);
}
catch (OperationCanceledException) { }
finally
{
    Log.CloseAndFlush();
}
```

---

## Graceful Shutdown

Pressing Ctrl+C triggers `Console.CancelKeyPress`. The handler sets `e.Cancel = true` — this prevents the process from terminating immediately — and calls `cts.Cancel()` to signal the `CancellationToken` passed to `server.StartAsync`.

`NatsServer.StartAsync` exits its accept loop on cancellation. In-flight client connections are left to drain naturally. After `StartAsync` returns (via `OperationCanceledException` which is caught), the `finally` block runs `Log.CloseAndFlush()` to ensure all buffered log output is written before the process exits.

---

## Testing

Run the full test suite with:

```bash
dotnet test
```

The test project is at `tests/NATS.Server.Tests/`. It uses xUnit with Shouldly for assertions.

### Test summary

69 tests across 6 test files:

| File | Tests | Coverage |
|------|-------|----------|
| `SubjectMatchTests.cs` | 33 | Subject validation and wildcard matching |
| `SubListTests.cs` | 12 | Trie insert, remove, match, queue groups, cache |
| `ParserTests.cs` | 14 | All command types, split packets, case insensitivity |
| `ClientTests.cs` | 2 | Socket-level INFO on connect, PING/PONG |
| `ServerTests.cs` | 3 | End-to-end accept, pub/sub, wildcard delivery |
| `IntegrationTests.cs` | 5 | NATS.Client.Core protocol compatibility |

### Test categories

**SubjectMatchTests** — 33 `[Theory]` cases verifying `SubjectMatch.IsValidSubject` (16 cases), `SubjectMatch.IsValidPublishSubject` (6 cases), and `SubjectMatch.MatchLiteral` (11 cases). Covers empty strings, leading/trailing dots, embedded spaces, `>` in non-terminal position, and all wildcard combinations.

**SubListTests** — 12 `[Fact]` tests exercising the `SubList` trie directly: literal insert and match, empty result, `*` wildcard at various token levels, `>` wildcard, root `>`, multiple overlapping subscriptions, remove, queue group grouping, `Count` tracking, and cache invalidation after a wildcard insert.

**ParserTests** — 14 `async [Fact]` tests that write protocol bytes into a `Pipe` and assert on the resulting `ParsedCommand` list. Covers `PING`, `PONG`, `CONNECT`, `SUB` (with and without queue group), `UNSUB` (with and without `max-messages`), `PUB` (with payload, with reply-to, zero payload), `HPUB` (with header), `INFO`, multiple commands in a single buffer, and case-insensitive parsing.

**ClientTests** — 2 `async [Fact]` tests using a real loopback socket pair. Verifies that `NatsClient` sends an `INFO` frame immediately on connection, and that it responds `PONG` to a `PING` after `CONNECT`.

**ServerTests** — 3 `async [Fact]` tests that start `NatsServer` on a random port. Verifies `INFO` on connect, basic pub/sub delivery (`MSG` format), and wildcard subscription matching.

**IntegrationTests** — 5 `async [Fact]` tests using the official `NATS.Client.Core` v2.7.2 NuGet package. Verifies end-to-end protocol compatibility with a real NATS client library: basic pub/sub, `*` wildcard delivery, `>` wildcard delivery, fan-out to two subscribers, and `PingAsync`.

Integration tests use `NullLoggerFactory.Instance` for the server so test output is not cluttered with server logs.

---

## Connecting with Standard NATS Clients

The server speaks the standard NATS wire protocol. Any NATS client library can connect to it.

```bash
# Using the nats CLI tool
nats sub "test.>" --server nats://127.0.0.1:4222
nats pub test.hello "world" --server nats://127.0.0.1:4222
```

From .NET, using `NATS.Client.Core`:

```csharp
var opts = new NatsOpts { Url = "nats://127.0.0.1:4222" };
await using var conn = new NatsConnection(opts);
await conn.ConnectAsync();
await conn.PublishAsync("test.hello", "world");
```

---

## Go Reference Server

The Go reference implementation can be built from `golang/nats-server/` for comparison testing:

```bash
# Build
cd golang/nats-server && go build

# Run on default port
./nats-server

# Run on custom port
./nats-server -p 14222
```

The Go server is useful for verifying that the .NET port produces identical protocol output and behaves the same way under edge-case client interactions.

---

## Current Limitations

The following features present in the Go reference server are not yet ported:

- Authentication — no username/password, token, NKey, or JWT support
- Clustering — no routes, gateways, or leaf nodes
- JetStream — no persistent streaming, streams, consumers, or RAFT
- Monitoring — no HTTP endpoints (`/varz`, `/connz`, `/healthz`, etc.)
- TLS — all connections are plaintext
- WebSocket — no WebSocket transport

---

## Related Documentation

- [Configuration Overview](../Configuration/Overview.md)
- [Server Overview](../Server/Overview.md)
- [Protocol Overview](../Protocol/Overview.md)

<!-- Last verified against codebase: 2026-02-22 -->