Fiber Middleware: Next vs Return

In this tutorial, you'll learn about Fiber Middleware: Next vs Return. We cover key concepts, practical examples, and best practices.

Middleware in Fiber -- Write Fiber middleware correctly using c.Next() inside the handler chain.

The Problem

Fiber middleware works like Express.js. Calling c.Next() invokes the next handler, then execution returns to the middleware. Return c.Next() for pre-only middleware.

Wrong

app.Use(func(c *fiber.Ctx) error {
    start := time.Now()
    c.Next()
    log.Printf("Request took %v", time.Since(start))
})

Output:

// Works but no explicit return

Right

app.Use(func(c *fiber.Ctx) error {
    start := time.Now()
    defer log.Printf("Request took %v", time.Since(start))
    return c.Next()
})
app.Use(recover.New())

Output:

$ curl http://localhost:8080/protected
// Logs duration after handler completes

Prevention

• Return c.Next() from middleware
• Use defer for post-handler cleanup
• To abort, return an error: return fiber.ErrUnauthorized
• Fiber has built-in CORS, CSRF, compression middleware
• Middleware order: Logger -> Recover -> CORS -> Auth -> Routes

Common Mistakes with fiber middleware

1. Placing the wildcard pattern first in case expressions, making all subsequent patterns unreachable
2. Using head and tail instead of pattern matching, causing runtime errors on empty lists
3. Forgetting that lazy evaluation defers computation until the value is forced, causing space leaks with unevaluated thunks

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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