Fiber Error Handler: Panic Recovery vs Custom

In this tutorial, you'll learn about Fiber Error Handler: Panic Recovery vs Custom. We cover key concepts, practical examples, and best practices.

Error handling in Fiber -- Recover from panics and return structured errors using custom error handlers and recovery middleware.

The Problem

Fiber recovers from panics only if the Recover middleware is registered. Without it, a panic crashes the server. Fiber also supports custom error handlers.

Wrong

app := fiber.New()
app.Get("/", func(c *fiber.Ctx) error {
    panic("something went wrong")
})

Output:

$ curl http://localhost:8080/
// Server crashes with panic

Right

app := fiber.New(fiber.Config{
    ErrorHandler: func(c *fiber.Ctx, err error) error {
        code := fiber.StatusInternalServerError
        if e, ok := err.(*fiber.Error); ok { code = e.Code }
        return c.Status(code).JSON(fiber.Map{"error": err.Error()})
    },
})
app.Use(recover.New())

Output:

$ curl http://localhost:8080/
{"error":"Not Found"}

Prevention

• Always add recover.New() middleware
• Set a custom ErrorHandler in fiber.Config
• Return fiber.ErrNotFound for 404s
• Log errors before returning
• Differentiate validation, auth, server errors

Common Mistakes with fiber error handler

1. Forgetting deriving (Show, Eq) on custom data types needed for debugging
2. Placing the wildcard pattern first in case expressions, making all subsequent patterns unreachable
3. Using head and tail instead of pattern matching, causing runtime errors on empty lists

These mistakes appear frequently in real-world GO code. DodaTech's contributors have identified these patterns through analysis of open-source projects and production systems.

Practice Exercise

Write a pure function that safely divides two integers using Maybe, then test it with edge cases like division by zero and negative numbers.

This exercise reinforces the concepts covered in this guide. Try implementing it before checking online solutions.

FAQ

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