error-handling.md

description
Fiber supports centralized error handling by returning an error to the handler which allows you to log errors to external services or send a customized HTTP response to the client.

🐛 Error Handling

Catching Errors

It’s essential to ensure that Fiber catches all errors that occur while running route handlers and middleware. You must return them to the handler function, where Fiber will catch and process them.

{% tabs %} {% tab title="Example" %}

app.Get("/", func(c *fiber.Ctx) error {
    // Pass error to Fiber
    return c.SendFile("file-does-not-exist")
})

{% endtab %} {% endtabs %}

Fiber does not handle panics by default. To recover from a panic thrown by any handler in the stack, you need to include the Recover middleware below:

{% code title="Example" %}

package main

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

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

    app.Use(recover.New())

    app.Get("/", func(c *fiber.Ctx) error {
        panic("This panic is caught by fiber")
    })

    log.Fatal(app.Listen(":3000"))
}

{% endcode %}

You could use Fiber's custom error struct to pass an additional status code using fiber.NewError(). It's optional to pass a message; if this is left empty, it will default to the status code message (404 equals Not Found).

{% code title="Example" %}

app.Get("/", func(c *fiber.Ctx) error {
    // 503 Service Unavailable
    return fiber.ErrServiceUnavailable

    // 503 On vacation!
    return fiber.NewError(fiber.StatusServiceUnavailable, "On vacation!")
})

{% endcode %}

Default Error Handler

Fiber provides an error handler by default. For a standard error, the response is sent as 500 Internal Server Error. If the error is of type fiber.Error, the response is sent with the provided status code and message.

{% code title="Example" %}

// Default error handler
var DefaultErrorHandler = func(c *fiber.Ctx, err error) error {
    // Default 500 statuscode
    code := fiber.StatusInternalServerError

    if e, ok := err.(*fiber.Error); ok {
        // Override status code if fiber.Error type
        code = e.Code
    }
    // Set Content-Type: text/plain; charset=utf-8
    c.Set(fiber.HeaderContentType, fiber.MIMETextPlainCharsetUTF8)

    // Return statuscode with error message
    return c.Status(code).SendString(err.Error())
}

{% endcode %}

Custom Error Handler

A custom error handler can be set using a Config when initializing a Fiber instance.

In most cases, the default error handler should be sufficient. However, a custom error handler can come in handy if you want to capture different types of errors and take action accordingly e.g., send a notification email or log an error to the centralized system. You can also send customized responses to the client e.g., error page or just a JSON response.

The following example shows how to display error pages for different types of errors.

{% code title="Example" %}

// Create a new fiber instance with custom config
app := fiber.New(fiber.Config{
    // Override default error handler
    ErrorHandler: func(ctx *fiber.Ctx, err error) error {
        // Status code defaults to 500
        code := fiber.StatusInternalServerError

        // Retrieve the custom status code if it's an fiber.*Error
        if e, ok := err.(*fiber.Error); ok {
            code = e.Code
        }

        // Send custom error page
        err = ctx.Status(code).SendFile(fmt.Sprintf("./%d.html", code))
        if err != nil {
            // In case the SendFile fails
            return ctx.Status(fiber.StatusInternalServerError).SendString("Internal Server Error")
        }

        // Return from handler
        return nil
    },
})

// ...

{% endcode %}

Special thanks to the Echo & Express framework for inspiration regarding error handling.