httpclient/README.md

# einherjar/httpclient

[![version](https://img.shields.io/badge/version-v1.0.0-5C4EE5?style=flat-square)](https://code.nochebuena.dev/einherjar/httpclient)
[![license](https://img.shields.io/badge/license-AGPL--3.0-22863A?style=flat-square)](LICENSE)
[![go](https://img.shields.io/badge/Go-1.26+-00ADD8?style=flat-square&logo=go&logoColor=white)](https://go.dev)

> To cross the realms, one must know the road — and how to wait when the bridge is down.

`code.nochebuena.dev/einherjar/httpclient` is the outbound HTTP client component of the Einherjar framework. It composes retry (via `avast/retry-go`) and a circuit breaker (via `sony/gobreaker`) behind a single `Provider` interface with one method: `Do`. Generic helpers `DoJSON` and `DoJSONRequest` reduce boilerplate for JSON APIs without hiding the underlying client.

---

## Usage

### Setup

```go
import "code.nochebuena.dev/einherjar/httpclient"

// With env-var config
client := httpclient.New(logger, httpclient.DefaultConfig())

// Or zero-config with defaults
client := httpclient.NewWithDefaults(logger)
```

`httpclient` is not a `lifecycle.Component` — it is stateless and requires no registration with the launcher.

### Sending requests

```go
req, err := http.NewRequestWithContext(ctx, http.MethodGet, "https://api.example.com/users", nil)
if err != nil {
    return err
}

resp, err := client.Do(req)
if err != nil {
    return err
}
defer resp.Body.Close()
```

### JSON GET helper

```go
type User struct {
    ID   string `json:"id"`
    Name string `json:"name"`
}

req, _ := http.NewRequestWithContext(ctx, http.MethodGet, "https://api.example.com/users/123", nil)
user, err := httpclient.DoJSON[User](ctx, client, req)
// user is *User on success
```

### JSON POST helper

```go
type CreateReq struct {
    Name  string `json:"name"`
    Email string `json:"email"`
}
type CreateResp struct {
    ID string `json:"id"`
}

resp, err := httpclient.DoJSONRequest[CreateReq, CreateResp](
    ctx, client,
    http.MethodPost, "https://api.example.com/users",
    CreateReq{Name: "Alice", Email: "alice@example.com"},
)
// resp is *CreateResp on success
```

### Error mapping

```go
// Map HTTP status codes to xerrors for consistent error handling
err := httpclient.MapStatusToError(resp.StatusCode, "upstream error")
// 400 → ErrInvalidInput
// 401 → ErrUnauthorized
// 403 → ErrPermissionDenied
// 404 → ErrNotFound
// 409 → ErrAlreadyExists
// 429 → ErrRateLimited
// 503 → ErrUnavailable
```

---

## Environment variables

| Variable | Required | Default | Description |
|---|---|---|---|
| `EINHERJAR_HTTP_CLIENT_NAME` | No | `http` | Circuit breaker name (appears in logs) |
| `EINHERJAR_HTTP_TIMEOUT` | No | `30s` | Total request timeout |
| `EINHERJAR_HTTP_DIAL_TIMEOUT` | No | `5s` | TCP connection timeout |
| `EINHERJAR_HTTP_MAX_RETRIES` | No | `3` | Maximum retry attempts |
| `EINHERJAR_HTTP_RETRY_DELAY` | No | `1s` | Delay between retries |
| `EINHERJAR_HTTP_CB_THRESHOLD` | No | `10` | Consecutive failures before circuit opens |
| `EINHERJAR_HTTP_CB_TIMEOUT` | No | `1m` | Time before circuit attempts half-open |

---

## Dependency graph

```
contracts  (zero dependencies)
    ↑
  core
    ↑
httpclient  (contracts, core, retry-go, gobreaker)
    ↑
  your app
```

---

## Verification

```bash
cd httpclient/
go build ./...
go vet ./...
go test ./...
gofmt -l .
```

---

> *A warrior who cannot reach the other realm is useless to the battle.*
> *Build the bridge. Make it resilient. Know when to wait.*