Skip to main content
Lightning gives you two ways to create an application: NewApp() for full control over configuration, and DefaultApp() as a batteries-included shortcut. Both accept the same Config struct.

​
Config fields

​
AppName
string
default:"lightning-app"
The name shown as a prefix in all log output produced by the application’s built-in logger.
​
JSONEncoder
JSONMarshal
A custom JSON marshaling function with the signature func(v any) ([]byte, error). When omitted, Lightning uses encoding/json.Marshal.
​
JSONDecoder
JSONUnmarshal
A custom JSON unmarshaling function with the signature func(data []byte, v any) error. When omitted, Lightning uses encoding/json.Unmarshal.
​
NotFoundHandler
HandlerFunc
A handler invoked when no route matches the incoming request. The default handler responds with 404 Not Found as plain text.
​
EnableDebug
bool
default:"false"
When true, Lightning registers a GET /__debug__/router_map endpoint that returns all registered routes as JSON. Useful for verifying route registration during development.
​
MaxRequestBodySize
int64
default:"0"
The maximum number of bytes the server reads from a request body. A value of 0 means unlimited. Requests that exceed this limit are rejected by the underlying fasthttp server.

​
NewApp()

NewApp accepts zero or one *Config argument. Any field you leave at its zero value falls back to the Lightning default for that field.

​
No configuration (all defaults)

package main

import "github.com/go-labx/lightning"

func main() {
    app := lightning.NewApp()

    app.Get("/ping", func(ctx *lightning.Context) {
        ctx.Text(lightning.StatusOK, "pong")
    })

    app.Run(":8080")
}

​
Custom configuration

package main

import "github.com/go-labx/lightning"

func main() {
    app := lightning.NewApp(&lightning.Config{
        AppName:            "payments-api",
        EnableDebug:        true,
        MaxRequestBodySize: 4 * 1024 * 1024, // 4 MB
        NotFoundHandler: func(ctx *lightning.Context) {
            ctx.JSON(lightning.StatusNotFound, lightning.Map{
                "error": "route not found",
                "path":  ctx.Path,
            })
        },
    })

    app.Get("/ping", func(ctx *lightning.Context) {
        ctx.Text(lightning.StatusOK, "pong")
    })

    app.Run(":8080")
}
You only need to set the fields you want to override. NewApp merges your Config on top of the defaults, so unset fields keep their default values.

​
DefaultApp()

DefaultApp is equivalent to calling NewApp() and then registering both the Logger and Recovery middleware: 
func DefaultApp() *Application {
    app := NewApp()
    app.Use(Logger())
    app.Use(Recovery())
    return app
}
Use DefaultApp when you want structured request logging and panic recovery without any extra setup: 
package main

import "github.com/go-labx/lightning"

func main() {
    app := lightning.DefaultApp()

    app.Get("/ping", func(ctx *lightning.Context) {
        ctx.Text(lightning.StatusOK, "pong")
    })

    app.Run(":8080")
}

​
Complete example

The following example shows a fully configured application with a custom JSON encoder, a branded 404 response, debug mode, and a 2 MB body size limit. 
package main

import (
    "encoding/json"

    "github.com/go-labx/lightning"
)

func main() {
    app := lightning.NewApp(&lightning.Config{
        AppName:            "inventory-service",
        EnableDebug:        true,
        MaxRequestBodySize: 2 * 1024 * 1024, // 2 MB
        JSONEncoder: func(v any) ([]byte, error) {
            return json.Marshal(v)
        },
        JSONDecoder: func(data []byte, v any) error {
            return json.Unmarshal(data, v)
        },
        NotFoundHandler: func(ctx *lightning.Context) {
            ctx.JSON(lightning.StatusNotFound, lightning.Map{
                "service": "inventory-service",
                "error":   "endpoint not found",
            })
        },
    })

    // Register middleware
    app.Use(lightning.Logger())
    app.Use(lightning.Recovery())

    // Routes
    app.Get("/items", func(ctx *lightning.Context) {
        ctx.JSON(lightning.StatusOK, lightning.Map{"items": []string{}})
    })

    app.Run(":8080")
}