# httpx

HTTP client and server toolkit for Go microservices. Client side: retry, load balancing, circuit breaking — all as `http.RoundTripper` middleware. Server side: routing, middleware (request ID, recovery, logging), health checks, graceful shutdown. stdlib only, zero external deps.

```
go get git.codelab.vc/pkg/httpx
```

## Quick start

```go
client := httpx.New(
    httpx.WithBaseURL("https://api.example.com"),
    httpx.WithTimeout(10*time.Second),
    httpx.WithRetry(retry.WithMaxAttempts(3)),
    httpx.WithMiddleware(
        middleware.UserAgent("my-service/1.0"),
        middleware.BearerAuth(func(ctx context.Context) (string, error) {
            return os.Getenv("API_TOKEN"), nil
        }),
    ),
)
defer client.Close()

resp, err := client.Get(ctx, "/users/123")
if err != nil {
    log.Fatal(err)
}

var user User
resp.JSON(&user)
```

## Packages

### Client

Client middleware is `func(http.RoundTripper) http.RoundTripper`. Use them with `httpx.Client` or plug into a plain `http.Client`.

| Package | What it does |
|---------|-------------|
| `retry` | Exponential/constant backoff, Retry-After support. Idempotent methods only by default. |
| `balancer` | Round robin, failover, weighted random. Optional background health checks. |
| `circuitbreaker` | Per-host state machine (closed/open/half-open). Stops hammering dead endpoints. |
| `middleware` | Logging (slog), default headers, bearer/basic auth, panic recovery. |

### Server

Server middleware is `func(http.Handler) http.Handler`. The `server` package provides a production-ready HTTP server.

| Component | What it does |
|-----------|-------------|
| `server.Server` | Wraps `http.Server` with graceful shutdown, signal handling, lifecycle logging. |
| `server.Router` | Lightweight wrapper around `http.ServeMux` with groups, prefix routing, sub-router mounting. |
| `server.RequestID` | Assigns/propagates `X-Request-Id` (UUID v4 via `crypto/rand`). |
| `server.Recovery` | Recovers panics, returns 500, logs stack trace. |
| `server.Logging` | Structured request logging (method, path, status, duration, request ID). |
| `server.HealthHandler` | Liveness (`/healthz`) and readiness (`/readyz`) endpoints with pluggable checkers. |
| `server.Defaults` | Production preset: RequestID → Recovery → Logging + sensible timeouts. |

The client assembles them in this order:

```
Request → Logging → Your Middleware → Retry → Circuit Breaker → Balancer → Transport
```

Retry wraps the circuit breaker and balancer, so each attempt can pick a different endpoint.

## Multi-DC setup

```go
client := httpx.New(
    httpx.WithEndpoints(
        balancer.Endpoint{URL: "https://dc1.api.internal", Weight: 3},
        balancer.Endpoint{URL: "https://dc2.api.internal", Weight: 1},
    ),
    httpx.WithBalancer(balancer.WithStrategy(balancer.WeightedRandom())),
    httpx.WithRetry(retry.WithMaxAttempts(4)),
    httpx.WithCircuitBreaker(circuitbreaker.WithFailureThreshold(5)),
    httpx.WithLogger(slog.Default()),
)
defer client.Close()
```

## Standalone usage

Each component works with any `http.Client`, no need for the full wrapper:

```go
// Just retry, nothing else
transport := retry.Transport(retry.WithMaxAttempts(3))
httpClient := &http.Client{
    Transport: transport(http.DefaultTransport),
}
```

```go
// Chain a few middlewares together
chain := middleware.Chain(
    middleware.Logging(slog.Default()),
    middleware.UserAgent("my-service/1.0"),
    retry.Transport(retry.WithMaxAttempts(2)),
)
httpClient := &http.Client{
    Transport: chain(http.DefaultTransport),
}
```

## Server

```go
logger := slog.Default()

r := server.NewRouter()
r.HandleFunc("GET /hello", func(w http.ResponseWriter, _ *http.Request) {
    w.Write([]byte("world"))
})

// Groups with middleware
api := r.Group("/api/v1", authMiddleware)
api.HandleFunc("GET /users/{id}", getUser)

// Health checks
r.Mount("/", server.HealthHandler(
    func() error { return db.Ping() },
))

srv := server.New(r, server.Defaults(logger)...)
log.Fatal(srv.ListenAndServe()) // graceful shutdown on SIGINT/SIGTERM
```

## Requirements

Go 1.24+, stdlib only.