chi

chi is a small, fast and expressive router / mux for Go HTTP services built with net/context.

Chi encourages writing services by composing small handlers and middlewares with many or few routes. Each middleware is like a layer of an onion connected through a consistent interface (http.Handler or chi.Handler) and a context.Context argument that flows down the layers during a request's lifecycle.

In order to get the most out of this pattern, chi's routing methods (Get, Post, Handle, Mount, etc.) support inline middlewares, middleware groups, and mounting (composing) any chi router to another - a bushel of onions. We've designed the Pressly API (150+ routes/handlers) exactly like this and its scaled very well.

Features

• Lightweight - cloc`d in ~600 LOC for the chi router
• Fast - yes, see benchmarks
• Expressive routing - middlewares, inline middleware groups/chains, and subrouter mounting
• Request context control (value chaining, deadlines and timeouts) - built on net/context
• Robust (tested, used in production)

Router design

Chi's router is based on a kind of Patricia Radix trie. Built on top of the tree is the Router interface:

// Register a middleware handler (or few) on the middleware stack
Use(middlewares ...interface{})

// Register a new middleware stack
Group(fn func(r Router)) Router

// Mount an inline sub-router
Route(pattern string, fn func(r Router)) Router

// Mount a sub-router
Mount(pattern string, handlers ...interface{})

// Register routing handler for all http methods
Handle(pattern string, handlers ...interface{})

// Register routing handler for CONNECT http method
Connect(pattern string, handlers ...interface{})

// Register routing handler for HEAD http method
Head(pattern string, handlers ...interface{})

// Register routing handler for GET http method
Get(pattern string, handlers ...interface{})

// Register routing handler for POST http method
Post(pattern string, handlers ...interface{})

// Register routing handler for PUT http method
Put(pattern string, handlers ...interface{})

// Register routing handler for PATCH http method
Patch(pattern string, handlers ...interface{})

// Register routing handler for DELETE http method
Delete(pattern string, handlers ...interface{})

// Register routing handler for TRACE http method
Trace(pattern string, handlers ...interface{})

// Register routing handler for OPTIONS http method
Options(pattern string, handlers ...interface{})

Each routing method accepts a URL pattern and chain of handlers. The URL pattern supports named params (ie. /users/:userID) and wildcards (ie. /admin/*).

The handlers argument can be a single request handler, or a chain of middleware handlers, followed by a request handler. The request handler is required, and must be the last argument.

We lose type checking of the handlers, but that'll be resolved sometime in the future, we hope, when Go's stdlib supports net/context in net/http. For now, chi checks the types at runtime and panics in case of a mismatch.

The supported handlers are as follows..

Middleware handlers

// Standard HTTP middleware. Compatible and friendly for when a request context isn't needed.
func StdMiddleware(next http.Handler) http.Handler {
  return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
    next.ServeHTTP(w, r)
  })
}

// net/context HTTP middleware. Useful for signaling to stop processing, adding a timeout,
// cancellation, or passing data down the middleware chain.
func CtxMiddleware(next chi.Handler) chi.Handler {
  return chi.HandlerFunc(func(ctx context.Context, w http.ResponseWriter, r *http.Request) {
    ctx = context.WithValue(ctx, "key", "value")
    next.ServeHTTPC(ctx, w, r)
  })
}

Request handlers

// Standard HTTP handler
func StdHandler(w http.ResponseWriter, r *http.Request) {
  w.Write([]byte("hi"))
}

// net/context HTTP request handler
func CtxHandler(ctx context.Context, w http.ResponseWriter, r *http.Request) {
  userID := chi.URLParams(ctx)["userID"] // from a route like /users/:userID
  key := ctx.Value("key").(string)
  w.Write([]byte(fmt.Sprintf("hi %v, %v", userID, key)))
}

net/context?

net/context is a tiny library written by Sameer Ajmani that provides a simple interface to signal context across call stacks and goroutines.

Learn more at https://blog.golang.org/context

and..

• Docs: https://godoc.org/golang.org/x/net/context
• Source: https://github.com/golang/net/tree/master/context
• net/http client managed by context.Context: https://github.com/golang/net/tree/master/context/ctxhttp

Examples

Examples: simple & rest

Preview:

import (
  //...
  "github.com/pressly/chi"
  "github.com/pressly/chi/middleware"
  "golang.org/x/net/context"
)

func main() {
  r := chi.NewRouter()

  // A good base middleware stack
  r.Use(middleware.RequestID)
  r.Use(middleware.RealIP)
  r.Use(middleware.Logger)
  r.Use(middleware.Recoverer)

  // When a client closes their connection midway through a request, the
  // http.CloseNotifier will cancel the request context (ctx).
  r.Use(middleware.CloseNotify)

  // Set a timeout value on the request context (ctx), that will signal
  // through ctx.Done() that the request has timed out and further
  // processing should be stopped.
  r.Use(middleware.Timeout(60 * time.Second))

  r.Get("/", func(w http.ResponseWriter, r *http.Request) {
    w.Write([]byte("hi"))
  })

  // RESTy routes for "articles" resource
  r.Route("/articles", func(r chi.Router) {
    r.Get("/", paginate, listArticles)  // GET /articles
    r.Post("/", createArticle)          // POST /articles

    r.Route("/:articleID", func(r chi.Router) {
      r.Use(ArticleCtx)
      r.Get("/", getArticle)            // GET /articles/123
      r.Put("/", updateArticle)         // PUT /articles/123
      r.Delete("/", deleteArticle)      // DELETE /articles/123
    })
  })

  // Mount the admin sub-router
  r.Mount("/admin", adminRouter())

  http.ListenAndServe(":3333", r)
}

func ArticleCtx(next chi.Handler) chi.Handler {
  return chi.HandlerFunc(func(ctx context.Context, w http.ResponseWriter, r *http.Request) {
    articleID := chi.URLParams(ctx)["articleID"]
    article, err := dbGetArticle(articleID)
    if err != nil {
      http.Error(w, http.StatusText(404), 404)
      return
    }
    ctx = context.WithValue(ctx, "article", article)
    next.ServeHTTPC(ctx, w, r)
  })
}

func getArticle(ctx context.Context, w http.ResponseWriter, r *http.Request) {
  article, ok := ctx.Value("article").(*Article)
  if !ok {
    http.Error(w, http.StatusText(422), 422)
    return
  }
  w.Write([]byte(fmt.Sprintf("title:%s", article.Title)))
}

// A completely separate router for administrator routes
func adminRouter() chi.Router {
  r := chi.NewRouter()
  r.Use(AdminOnly)
  r.Get("/", adminIndex)
  r.Get("/accounts", adminListAccounts)
  return r
}

func AdminOnly(next chi.Handler) chi.Handler {
  return chi.HandlerFunc(func(ctx context.Context, w http.ResponseWriter, r *http.Request) {
    perm, ok := ctx.Value("acl.permission").(YourPermissionType)
    if !ok || !perm.IsAdmin() {
      http.Error(w, http.StatusText(403), 403)
      return
    }
    next.ServeHTTPC(ctx, w, r)
  })
}

Middlewares

Chi comes equipped with an optional middleware package, providing:

---

Middleware	Description
RequestID	Injects a request ID into the context of each request.
RealIP	Sets a http.Request's RemoteAddr to either X-Forwarded-For or X-Real-IP.
Logger	Logs the start and end of each request with the elapsed processing time.
Recoverer	Gracefully absorb panics and prints the stack trace.
NoCache	Sets response headers to prevent clients from caching.
CloseNotify	Signals to the request context when a client has closed their connection.
Timeout	Signals to the request context when the timeout deadline is reached.
Throttle	Puts a ceiling on the number of concurrent requests.

---

Other middlewares:

• httpcoala - request coalescer
• jwtauth - JWT authenticator

please submit a PR if you'd like to include a link to a chi middleware

Future

We're hoping that by Go 1.7 (in 2016), net/context will be in the Go stdlib and net/http will support context.Context. You'll notice that chi.Handler and http.Handler are very similar and the middleware signatures follow the same structure. One day chi.Handler will be deprecated and the router will live on just as it is without any dependencies beyond stdlib. And... then, we have infinitely more middlewares to compose from the community!!

See discussions:

• golang/go#13021
• https://groups.google.com/forum/#!topic/golang-dev/cQs1z9LrJDU

Benchmarks

The benchmark suite: https://github.com/pkieltyka/go-http-routing-benchmark

The results as of Nov. 6, 2015 - https://gist.github.com/pkieltyka/505b07b09f5c63e36ef5

Note: by design, chi allocates new routing URLParams map for each request, as opposed to reusing URLParams from a pool.

Credits

• Carl Jackson for https://github.com/zenazn/goji
  • Parts of Chi's thinking comes from goji, and Chi's middleware package sources from goji.
• Armon Dadgar for https://github.com/armon/go-radix
• Contributions: @VojtechVitek

TODO

• Mux options
  • Trailing slash?
  • Case insensitive paths?
  • GET for HEAD requests (auto fallback)?
• Register not found handler
• Register error handler (500's)
• HTTP2 example
  • both http 1.1 and http2 automatically.. just turn it on :)
• Websocket example
• Regexp support in router "/:id([0-9]+)" or "#id^[0-9]+$" or ..

We'll be more than happy to see your contributions!

License

Copyright (c) 2015 Peter Kieltyka

Licensed under MIT License