Lion is a fast HTTP router for building modern scalable modular REST APIs in Go
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Lion Build Status GoDoc License Go Report Card

Lion is a fast HTTP router for building modern scalable modular REST APIs written in Go (golang).


  • Go1-like guarantee: The API will not change in Lion v2.x (once released).
  • Modular: You can define your own modules to easily build a scalable architecture
  • RESTful: You can define modules to groups http resources together.
  • Subdomains: Select which subdomains, hosts a router can match. You can specify it a param or a wildcard e.g. * More infos here.
  • Near zero garbage: Lion generates near zero garbage*. The allocations generated comes from the net/http.Request.WithContext() works. It makes a shallow copy of the request.

Table of contents


Lion requires Go 1.7+:

$ go get -u

Next versions of Lion will support the latest Go version and the previous one. For example, when Go 1.8 is out, Lion will support Go 1.7 and Go 1.8.

Hello World

package main

import (


func Home(w http.ResponseWriter, r *http.Request) {
	fmt.Fprintf(w, "Home")

func Hello(w http.ResponseWriter, r *http.Request) {
	name := lion.Param(r, "name")
	fmt.Fprintf(w, "Hello %s!",name)

func main() {
	l := lion.Classic()
	l.GetFunc("/", Home)
	l.GetFunc("/hello/:name", Hello)

Try it yourself by running the following command from the current directory:

$ go run examples/hello/hello.go

Getting started with modules and resources

We are going to build a sample products listing REST api (without database handling to keep it simple):

func main() {
	l := lion.Classic()
	api := l.Group("/api")

// Products module is accessible at url: /api/products
// It handles getting a list of products or creating a new product
type Products struct{}

func (p Products) Base() string {
	return "/products"

func (p Products) Get(w http.ResponseWriter, r *http.Request) {
	fmt.Fprintf(w, "Fetching all products")

func (p Products) Post(w http.ResponseWriter, r *http.Request) {
	fmt.Fprintf(w, "Creating a new product")

func (p Products) Routes(r *lion.Router) {
	// Defining a resource for getting, editing and deleting a single product
	r.Resource("/:id", OneProduct{})

// OneProduct resource is accessible at url: /api/products/:id
// It handles getting, editing and deleting a single product
type OneProduct struct{}

func (p OneProduct) Get(w http.ResponseWriter, r *http.Request) {
	id := lion.Param(r, "id")
	fmt.Fprintf(w, "Getting product: %s", id)

func (p OneProduct) Put(w http.ResponseWriter, r *http.Request) {
	id := lion.Param(r, "id")
	fmt.Fprintf(w, "Updating article: %s", id)

func (p OneProduct) Delete(w http.ResponseWriter, r *http.Request) {
	id := lion.Param(r, "id")
	fmt.Fprintf(w, "Deleting article: %s", id)

Try it yourself. Run:

$ go run examples/modular-hello/modular-hello.go

Open your web browser to http://localhost:3000/api/products or http://localhost:3000/api/products/123. You should see "Fetching all products" or "Getting product: 123".

Using net/http.Handler

Handlers should implement the native net/http.Handler:

l.Get("/get", get)
l.Post("/post", post)
l.Put("/put", put)
l.Delete("/delete", delete)

Using net/http.HandlerFunc

You can use native net/http.Handler (func(w http.ResponseWriter, r *http.Request)):

func myHandlerFunc(w http.ResponseWriter, r *http.Request)  {
  fmt.Fprintf(w, "Hi!")

l.GetFunc("/get", myHandlerFunc)
l.PostFunc("/post", myHandlerFunc)
l.PutFunc("/put", myHandlerFunc)
l.DeleteFunc("/delete", myHandlerFunc)


Middlewares should implement the Middleware interface:

type Middleware interface {
	ServeNext(http.Handler) http.Handler

The ServeNext function accepts a http.Handler and returns a http.Handler.

You can also use MiddlewareFuncs which are basically just func(http.Handler) http.Handler

For example:

func middlewareFunc(next Handler) Handler  {
	return next

Using Named Middlewares

Named middlewares are designed to be able to reuse a previously defined middleware. For example, if you have a EnsureAuthenticated middleware that check whether a user is logged in. You can define it once and reuse later in your application.

l := lion.New()
l.Define("EnsureAuthenticated", NewEnsureAuthenticatedMiddleware())

To reuse it later in your application, you can use the UseNamed method. If it cannot find the named middleware if the current Router instance it will try to find it in the parent router. If a named middleware is not found it will panic.

api := l.Group("/api")

Using Third-Party Middlewares


In v1, negroni was supported directly using UseNegroni. It still works but you will have to use .UseNext and pass it a negroni.HandlerFunc: func(rw http.ResponseWriter, r *http.Request, next http.HandlerFunc)

This way if you prefer to use this kind of middleware, you can.

You can use Negroni middlewares you can find a list of third party middlewares here

l := lion.New()

Matching Subdomains/Hosts

You can match a specific or multiple hosts. You can use patterns in the same way they are currently used for routes with only some edge cases. The main difference is that you will have to use the '$' character instead of ':' to define a parameter. will match $ will match will not match * will match

l := New()

// Group by /api basepath
api := l.Group("/api")

// Specific to v1
v1 := api.Subrouter().

v1.Get("/", v1Handler)

// Specific to v2
v2 := api.Subrouter().

v2.Get("/", v2Handler)


You can define a resource to represent a REST, CRUD api resource. You define global middlewares using Uses() method. For defining custom middlewares for each http method, you have to create a function which name is composed of the http method suffixed by "Middlewares". For example, if you want to define middlewares for the Get method you will have to create a method called: GetMiddlewares().

A resource is defined by the following methods. Everything is optional:

// Global middlewares for the resource (Optional)
Uses() Middlewares

// Middlewares for the http methods (Optional)
GetMiddlewares() Middlewares
PostMiddlewares() Middlewares
PutMiddlewares() Middlewares
DeleteMiddlewares() Middlewares

// HandlerFuncs for each HTTP Methods (Optional)
Get(w http.ResponseWriter, r *http.Request)
Post(w http.ResponseWriter, r *http.Request)
Put(w http.ResponseWriter, r *http.Request)
Delete(w http.ResponseWriter, r *http.Request)


package main

type todolist struct{}

func (t todolist) Uses() lion.Middlewares {
	return lion.Middlewares{lion.NewLogger()}

func (t todolist) Get(w http.ResponseWriter, r *http.Request) {
	fmt.Fprintf(w, "getting todos")

func main() {
	l := lion.New()
	l.Resource("/todos", todolist{})

## Modules

Modules are a way to modularize an api which can then define submodules, subresources and custom routes. A module is defined by the following methods:

// Required: Base url pattern of the module
Base() string

// Routes accepts a Router instance. This method is used to define the routes of this module.
// Each routes defined are relative to the Base() url pattern

// Optional: Requires named middlewares. Refer to Named Middlewares section
Requires() []string
package main

type api struct{}

// Required: Base url
func (t api) Base() string { return "/api" }

// Required: Here you can declare sub-resources, submodules and custom routes.
func (t api) Routes(r *lion.Router) {
	r.Get("/custom", t.CustomRoute)

// Optional: Attach Get method to this Module.
// ====> A Module is also a Resource.
func (t api) Get(w http.ResponseWriter, r *http.Request) {
	fmt.Fprintf(w, "This also a resource accessible at http://localhost:3000/api")

// Optional: Defining custom routes
func (t api) CustomRoute(w http.ResponseWriter, r *http.Request) {
	fmt.Fprintf(w, "This a custom route for this module http://localhost:3000/api/")

func main() {
	l := lion.New()
	// Registering the module


Using GET, POST, PUT, DELETE http methods

l := lion.Classic()

// Using Handlers
l.Get("/get", get)
l.Post("/post", post)
l.Put("/put", put)
l.Delete("/delete", delete)

// Using functions
l.GetFunc("/get", getFunc)
l.PostFunc("/post", postFunc)
l.PutFunc("/put", putFunc)
l.DeleteFunc("/delete", deleteFunc)


Using middlewares

func main() {
	l := lion.Classic()

	// Using middleware

	// Using middleware functions

	l.GetFunc("/hello/:name", Hello)


Group routes by a base path

l := lion.Classic()
api := l.Group("/api")

v1 := l.Group("/v1")
v1.GetFunc("/somepath", gettingFromV1)

v2 := l.Group("/v2")
v2.GetFunc("/somepath", gettingFromV2)


Mounting a router into a base path

l := lion.Classic()

sub := lion.New()
sub.GetFunc("/somepath", getting)

l.Mount("/api", sub)

Default middlewares

lion.Classic() creates a router with default middlewares (Recovery, RealIP, Logger, Static). If you wish to create a blank router without any middlewares you can use lion.New().

func main()  {
	// This a no middlewares registered
	l := lion.New()

	l.GetFunc("/hello/:name", Hello)


Custom Middlewares

Custom middlewares should implement the Middleware interface:

type Middleware interface {
	ServeNext(Handler) Handler

You can also make MiddlewareFuncs to use using .UseFunc() method. It has to accept a Handler and return a Handler:

func(next Handler) Handler

Custom Logger example

type logger struct{}

func (*logger) ServeNext(next lion.Handler) lion.Handler {
	return lion.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		start := time.Now()

		next.ServeHTTPC(c, w, r)

		fmt.Printf("Served %s in %s\n", r.URL.Path, time.Since(start))

Then in the main function you can use the middleware using:

l := lion.New()

l.GetFunc("/hello/:name", Hello)


TODO: Update this when v2 is released.


Want to contribute to Lion ? Awesome! Feel free to submit an issue or a pull request.

Here are some ways you can help:

  • Report bugs
  • Share a middleware or a module
  • Improve code/documentation
  • Propose new features
  • and more...


The project is licensed under the MIT license available here:

The benchmarks present in bench_test.go is licensed under a BSD-style license available here:


  • [x] Support for Go 1.7 context
  • [x] Host matching
  • [x] Automatic OPTIONS handler
  • [ ] Modules
    • [ ] JWT Auth module
  • [x] Better static file handling
  • [ ] More documentation


Lion v1 was inspired by pressly/chi. If Lion is not the right http router for you, check out chi.

Parts of Lion taken for other projects:

  • Negroni
    • Static and Recovery middlewares are taken from Negroni
  • Goji
    • RealIP middleware is taken from goji
  • Gin
    • ResponseWriter and Logger inspiration are inspired by gin
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