Fiber Core Knowledge

Full Reference: See advanced.md for validation with go-playground/validator, WebSocket setup, custom error handling, prefork mode, and graceful shutdown.

Deep Knowledge: Use mcp__documentation__fetch_docs with technology: fiber for comprehensive documentation.

Basic Setup

package main

import "github.com/gofiber/fiber/v2"

func main() {
    app := fiber.New()

    app.Get("/", func(c *fiber.Ctx) error {
        return c.SendString("Hello, World!")
    })

    app.Listen(":8080")
}

Configuration

app := fiber.New(fiber.Config{
    Prefork:       true,               // Multiple processes
    StrictRouting: true,               // /foo != /foo/
    CaseSensitive: true,               // /Foo != /foo
    BodyLimit:     4 * 1024 * 1024,    // 4MB
    ReadTimeout:   10 * time.Second,
    WriteTimeout:  10 * time.Second,
})

Routing

app.Get("/users", listUsers)
app.Get("/users/:id", getUser)
app.Post("/users", createUser)
app.Put("/users/:id", updateUser)
app.Delete("/users/:id", deleteUser)

// Path parameters
app.Get("/users/:id", func(c *fiber.Ctx) error {
    id := c.Params("id")
    return c.JSON(fiber.Map{"id": id})
})

// Optional parameter
app.Get("/users/:name?", func(c *fiber.Ctx) error {
    name := c.Params("name", "anonymous")
    return c.JSON(fiber.Map{"name": name})
})

// Route groups
api := app.Group("/api")
v1 := api.Group("/v1")
v1.Get("/users", listUsersV1)

Context - Request Data

app.Post("/users", func(c *fiber.Ctx) error {
    // Path params
    id := c.Params("id")
    idInt, _ := c.ParamsInt("id")

    // Query params
    page := c.Query("page", "1")
    pageInt := c.QueryInt("page", 1)

    // Headers
    auth := c.Get("Authorization")

    // Cookies
    session := c.Cookies("session_id")

    return c.SendStatus(fiber.StatusOK)
})

Body Parsing

type CreateUserRequest struct {
    Name  string `json:"name"`
    Email string `json:"email"`
}

app.Post("/users", func(c *fiber.Ctx) error {
    var req CreateUserRequest
    if err := c.BodyParser(&req); err != nil {
        return c.Status(fiber.StatusBadRequest).JSON(fiber.Map{
            "error": err.Error(),
        })
    }
    return c.Status(fiber.StatusCreated).JSON(req)
})

Middleware

import (
    "github.com/gofiber/fiber/v2/middleware/logger"
    "github.com/gofiber/fiber/v2/middleware/recover"
    "github.com/gofiber/fiber/v2/middleware/cors"
    "github.com/gofiber/fiber/v2/middleware/limiter"
)

app.Use(recover.New())
app.Use(logger.New())

app.Use(cors.New(cors.Config{
    AllowOrigins: "https://example.com",
    AllowMethods: "GET,POST,PUT,DELETE",
}))

app.Use(limiter.New(limiter.Config{
    Max:        100,
    Expiration: 1 * time.Minute,
}))

Health Checks

app.Get("/health", func(c *fiber.Ctx) error {
    return c.JSON(fiber.Map{"status": "healthy"})
})

app.Get("/ready", func(c *fiber.Ctx) error {
    if err := db.Ping(); err != nil {
        return c.Status(fiber.StatusServiceUnavailable).JSON(fiber.Map{
            "status": "not ready",
        })
    }
    return c.JSON(fiber.Map{"status": "ready"})
})

When NOT to Use This Skill

• Gin projects - Gin has different context API
• Echo projects - Echo has different middleware patterns
• Chi projects - Chi is stdlib-compatible
• Standard net/http required - Fiber uses fasthttp, not net/http
• gRPC services - Fiber doesn't support gRPC

Anti-Patterns

Anti-Pattern	Why It's Bad	Solution
Not calling c.Next() in middleware	Breaks middleware chain	Always call c.Next() unless stopping
Using c.Body() multiple times	Body is consumed	Store body in variable first
Missing error handling	Silent failures	Check BodyParser() return value
Not setting Prefork carefully	May cause issues with state	Only use Prefork without shared state
No rate limiting	DDoS vulnerability	Use limiter middleware

Quick Troubleshooting

Problem	Diagnosis	Fix
Route not found	Wrong method or path	Check exact route registration
Body parsing fails	Wrong content-type	Ensure Content-Type header is correct
CORS errors	Not configured	Use cors.New() middleware
Middleware not executing	Wrong order	Place before route handlers
Prefork issues	Shared state problems	Avoid shared mutable state with Prefork

Production Checklist

• Recovery middleware enabled
• CORS configured
• Rate limiting enabled
• Request body size limit set
• Timeouts configured
• Structured logging
• Health/readiness endpoints
• Graceful shutdown
• Input validation

Reference Documentation

• Routing
• Context
• Middleware