Imported from oimiragieo/agent-studio (.claude/skills/fiber-logging-and-project-structure/SKILL.md). Install upstream with npx skills add oimiragieo/agent-studio --skill fiber-logging-and-project-structure. Copyright stays with the author.

Fiber Logging And Project Structure Skill

Project Structure (Standard Go Layout)

• Organize all Fiber applications using: cmd/<appname>/main.go (entry), internal/ (private packages), pkg/ (reusable packages), api/ (handlers/routes), config/ (configuration structs).
• Never put business logic in cmd/ — keep main.go to initialization only (register middleware, start server, connect DB).
• Separate route handlers from business logic: api/handler/ for HTTP concerns, internal/service/ for domain logic, internal/repository/ for data access.

Logging

• Use structured logging: zerolog (preferred for Fiber) or zap. Never use fmt.Println or stdlib log in production handlers.
• Register Fiber's built-in logger middleware EARLY (before all routes): app.Use(logger.New()).
• Fiber v3 logger middleware: import from github.com/gofiber/fiber/v3/middleware/logger.
• Add correlation IDs in middleware using ctx.Locals("requestID", uuid.New()) and include in every log entry.
• Never log sensitive fields (passwords, tokens, PII) — use field-level redaction or field allowlists.

Middleware Registration Order

• Register global middleware before routes: Logger → RequestID → CORS → RateLimiter → Auth → Routes.
• Middleware registered via app.Use() applies to all subsequent routes; placement matters.
• Route-specific middleware: apply as a second argument to app.Get("/path", authMiddleware, handler).

Environment Configuration

• Load config at startup via viper, envconfig, or godotenv — never read os.Getenv() scattered in handlers.
• Define a typed config struct: type Config struct { Port string \env:"PORT" envDefault:"3000"` }`.
• Provide .env.example with all required variables; never commit .env files.
• Fail fast on missing required config: panic or log.Fatal during startup if required env vars are absent.

Error Handling

• Return fiber.NewError(fiber.StatusBadRequest, "message") from handlers for HTTP errors.
• Use a global error handler via app.Config().ErrorHandler to produce consistent JSON error responses.
• Never expose internal error details or stack traces in production error responses.

import ( "log" "github.com/gofiber/fiber/v2" "github.com/gofiber/fiber/v2/middleware/logger" "github.com/gofiber/fiber/v2/middleware/requestid" "myapp/internal/config" "myapp/api/routes" )

func main() { cfg := config.Load() // typed config, fails fast on missing vars

app := fiber.New(fiber.Config{
    ErrorHandler: func(c *fiber.Ctx, err error) error {
        return c.Status(fiber.StatusInternalServerError).JSON(fiber.Map{"error": err.Error()})
    },
})

// Middleware: register BEFORE routes
app.Use(requestid.New())
app.Use(logger.New(logger.Config{
    Format: "${time} ${method} ${path} ${status} ${latency}\n",
}))

routes.Register(app)           // all routes in internal/api/routes/
log.Fatal(app.Listen(cfg.Port))

}

// internal/config/config.go — typed config type Config struct { Port string `env:"PORT" envDefault:":3000"` DBUrl string `env:"DATABASE_URL,required"` }

</examples>

## Iron Laws

1. **ALWAYS** use structured logging (zerolog or logrus with JSON output) — never use `fmt.Println` or `log.Printf` in production Fiber applications; unstructured logs cannot be parsed by log aggregators.
2. **NEVER** put business logic in route handlers — always call a service/controller layer; route handlers must only handle HTTP concerns (parsing, validation, response writing).
3. **ALWAYS** use Fiber's `ctx.Locals()` for request-scoped values (user ID, trace ID) — never pass request-scoped data via global variables or function parameters down the call stack.
4. **NEVER** commit sensitive configuration directly in code — use `envconfig`, `viper`, or environment variables with a `.env.example` template; loaded secrets must never appear in logs.
5. **ALWAYS** organize project structure into `cmd/`, `internal/`, `pkg/` conventions — Fiber projects that put all code in root packages become unmaintainable at scale.

## Anti-Patterns

| Anti-Pattern                                | Why It Fails                                                            | Correct Approach                                                         |
| ------------------------------------------- | ----------------------------------------------------------------------- | ------------------------------------------------------------------------ |
| `fmt.Println` for logging in Fiber handlers | Unstructured; no log levels; no correlation IDs; breaks log aggregation | Use zerolog or logrus with `zap.String("key", value)` structured fields  |
| Business logic in route handlers            | Logic becomes untestable and non-reusable; couples HTTP layer to domain | Move to service layer; handler calls service method, formats response    |
| Global state for request context            | Concurrent requests overwrite each other's context; race conditions     | Use `ctx.Locals("key", value)` for all request-scoped data               |
| Hardcoded config values                     | No environment-specific deployments; credentials in source history      | Use `envconfig` or `viper` with `.env.example`; never commit real values |
| All files in project root                   | Impossible to separate public/internal APIs; package import cycles      | Use standard Go layout: `cmd/`, `internal/`, `pkg/`, `api/`              |

## Memory Protocol (MANDATORY)

**Before starting:**

```bash
cat .claude/context/memory/learnings.md

After completing: Record any new patterns or exceptions discovered.

ASSUME INTERRUPTION: Your context may reset. If it's not in memory, it didn't happen.