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chi is a lightweight, idiomatic and composable router for building Go HTTP services. It's especially good at helping you write large REST API services that are kept maintainable as your project grows and changes. chi is built on the new context package introduced in Go 1.7 to handle signaling, cancelation and request-scoped values across a handler chain.

The focus of the project has been to seek out an elegant and comfortable design for writing REST API servers, written during the development of the Pressly API service that powers our public API service, which in turn powers all of our client-side applications.

The key considerations of chi's design are: project structure, maintainability, standard http handlers (stdlib-only), developer productivity, and deconstructing a large system into many small parts. The core router github.com/go-chi/chi is quite small (less than 1000 LOC), but we've also included some useful/optional subpackages: middleware, render and docgen. We hope you enjoy it too!

Install

go get -u github.com/go-chi/chi

Features

Lightweight - cloc'd in ~1000 LOC for the chi router
Fast - yes, see benchmarks
100% compatible with net/http - use any http or middleware pkg in the ecosystem that is also compatible with net/http
Designed for modular/composable APIs - middlewares, inline middlewares, route groups and subrouter mounting
Context control - built on new context package, providing value chaining, cancellations and timeouts
Robust - in production at Pressly, CloudFlare, Heroku, 99Designs, and many others (see discussion)
Doc generation - docgen auto-generates routing documentation from your source to JSON or Markdown
No external dependencies - plain ol' Go stdlib + net/http

Examples

See _examples/ for a variety of examples.

As easy as:

package main

import (
	"net/http"

	"github.com/go-chi/chi"
	"github.com/go-chi/chi/middleware"
)

func main() {
	r := chi.NewRouter()
	r.Use(middleware.Logger)
	r.Get("/", func(w http.ResponseWriter, r *http.Request) {
		w.Write([]byte("welcome"))
	})
	http.ListenAndServe(":3000", r)
}

REST Preview:

Here is a little preview of how routing looks like with chi. Also take a look at the generated routing docs in JSON (routes.json) and in Markdown (routes.md).

I highly recommend reading the source of the examples listed above, they will show you all the features of chi and serve as a good form of documentation.

import (
  //...
  "context"
  "github.com/go-chi/chi"
  "github.com/go-chi/chi/middleware"
)

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)

  // 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.With(paginate).Get("/", listArticles)                           // GET /articles
    r.With(paginate).Get("/{month}-{day}-{year}", listArticlesByDate) // GET /articles/01-16-2017

    r.Post("/", createArticle)                                        // POST /articles
    r.Get("/search", searchArticles)                                  // GET /articles/search

    // Regexp url parameters:
    r.Get("/{articleSlug:[a-z-]+}", getArticleBySlug)                // GET /articles/home-is-toronto

    // Subrouters:
    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 http.Handler) http.Handler {
  return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
    articleID := chi.URLParam(r, "articleID")
    article, err := dbGetArticle(articleID)
    if err != nil {
      http.Error(w, http.StatusText(404), 404)
      return
    }
    ctx := context.WithValue(r.Context(), "article", article)
    next.ServeHTTP(w, r.WithContext(ctx))
  })
}

func getArticle(w http.ResponseWriter, r *http.Request) {
  ctx := r.Context()
  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() http.Handler {
  r := chi.NewRouter()
  r.Use(AdminOnly)
  r.Get("/", adminIndex)
  r.Get("/accounts", adminListAccounts)
  return r
}

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

Router interface

chi's router is based on a kind of Patricia Radix trie. The router is fully compatible with net/http.

Built on top of the tree is the Router interface:

// Router consisting of the core routing methods used by chi's Mux,
// using only the standard net/http.
type Router interface {
	http.Handler
	Routes

	// Use appends one or more middlewares onto the Router stack.
	Use(middlewares ...func(http.Handler) http.Handler)

	// With adds inline middlewares for an endpoint handler.
	With(middlewares ...func(http.Handler) http.Handler) Router

	// Group adds a new inline-Router along the current routing
	// path, with a fresh middleware stack for the inline-Router.
	Group(fn func(r Router)) Router

	// Route mounts a sub-Router along a `pattern`` string.
	Route(pattern string, fn func(r Router)) Router

	// Mount attaches another http.Handler along ./pattern/*
	Mount(pattern string, h http.Handler)

	// Handle and HandleFunc adds routes for `pattern` that matches
	// all HTTP methods.
	Handle(pattern string, h http.Handler)
	HandleFunc(pattern string, h http.HandlerFunc)

	// Method and MethodFunc adds routes for `pattern` that matches
	// the `method` HTTP method.
	Method(method, pattern string, h http.Handler)
	MethodFunc(method, pattern string, h http.HandlerFunc)

	// HTTP-method routing along `pattern`
	Connect(pattern string, h http.HandlerFunc)
	Delete(pattern string, h http.HandlerFunc)
	Get(pattern string, h http.HandlerFunc)
	Head(pattern string, h http.HandlerFunc)
	Options(pattern string, h http.HandlerFunc)
	Patch(pattern string, h http.HandlerFunc)
	Post(pattern string, h http.HandlerFunc)
	Put(pattern string, h http.HandlerFunc)
	Trace(pattern string, h http.HandlerFunc)

	// NotFound defines a handler to respond whenever a route could
	// not be found.
	NotFound(h http.HandlerFunc)

	// MethodNotAllowed defines a handler to respond whenever a method is
	// not allowed.
	MethodNotAllowed(h http.HandlerFunc)
}

// Routes interface adds two methods for router traversal, which is also
// used by the github.com/go-chi/docgen package to generate documentation for Routers.
type Routes interface {
	// Routes returns the routing tree in an easily traversable structure.
	Routes() []Route

	// Middlewares returns the list of middlewares in use by the router.
	Middlewares() Middlewares

	// Match searches the routing tree for a handler that matches
	// the method/path - similar to routing a http request, but without
	// executing the handler thereafter.
	Match(rctx *Context, method, path string) bool
}

Each routing method accepts a URL pattern and chain of handlers. The URL pattern supports named params (ie. /users/{userID}) and wildcards (ie. /admin/*). URL parameters can be fetched at runtime by calling chi.URLParam(r, "userID") for named parameters and chi.URLParam(r, "*") for a wildcard parameter.

Middleware handlers

chi's middlewares are just stdlib net/http middleware handlers. There is nothing special about them, which means the router and all the tooling is designed to be compatible and friendly with any middleware in the community. This offers much better extensibility and reuse of packages and is at the heart of chi's purpose.

Here is an example of a standard net/http middleware where we assign a context key "user" the value of "123". This middleware sets a hypothetical user identifier on the request context and calls the next handler in the chain.

// HTTP middleware setting a value on the request context
func MyMiddleware(next http.Handler) http.Handler {
  return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
    // create new context from `r` request context, and assign key `"user"`
    // to value of `"123"`
    ctx := context.WithValue(r.Context(), "user", "123")

    // call the next handler in the chain, passing the response writer and
    // the updated request object with the new context value.
    //
    // note: context.Context values are nested, so any previously set
    // values will be accessible as well, and the new `"user"` key
    // will be accessible from this point forward.
    next.ServeHTTP(w, r.WithContext(ctx))
  })
}

Request handlers

chi uses standard net/http request handlers. This little snippet is an example of a http.Handler func that reads a user identifier from the request context - hypothetically, identifying the user sending an authenticated request, validated+set by a previous middleware handler.

// HTTP handler accessing data from the request context.
func MyRequestHandler(w http.ResponseWriter, r *http.Request) {
  // here we read from the request context and fetch out `"user"` key set in
  // the MyMiddleware example above.
  user := r.Context().Value("user").(string)

  // respond to the client
  w.Write([]byte(fmt.Sprintf("hi %s", user)))
}

URL parameters

chi's router parses and stores URL parameters right onto the request context. Here is an example of how to access URL params in your net/http handlers. And of course, middlewares are able to access the same information.

// HTTP handler accessing the url routing parameters.
func MyRequestHandler(w http.ResponseWriter, r *http.Request) {
  // fetch the url parameter `"userID"` from the request of a matching
  // routing pattern. An example routing pattern could be: /users/{userID}
  userID := chi.URLParam(r, "userID")

  // fetch `"key"` from the request context
  ctx := r.Context()
  key := ctx.Value("key").(string)

  // respond to the client
  w.Write([]byte(fmt.Sprintf("hi %v, %v", userID, key)))
}

Middlewares

chi comes equipped with an optional middleware package, providing a suite of standard net/http middlewares. Please note, any middleware in the ecosystem that is also compatible with net/http can be used with chi's mux.

Core middlewares

chi/middleware Handler	description
AllowContentType	Explicit whitelist of accepted request Content-Types
BasicAuth	Basic HTTP authentication
Compress	Gzip compression for clients that accept compressed responses
GetHead	Automatically route undefined HEAD requests to GET handlers
Heartbeat	Monitoring endpoint to check the servers pulse
Logger	Logs the start and end of each request with the elapsed processing time
NoCache	Sets response headers to prevent clients from caching
Profiler	Easily attach net/http/pprof to your routers
RealIP	Sets a http.Request's RemoteAddr to either X-Forwarded-For or X-Real-IP
Recoverer	Gracefully absorb panics and prints the stack trace
RequestID	Injects a request ID into the context of each request
RedirectSlashes	Redirect slashes on routing paths
SetHeader	Short-hand middleware to set a response header key/value
StripSlashes	Strip slashes on routing paths
Throttle	Puts a ceiling on the number of concurrent requests
Timeout	Signals to the request context when the timeout deadline is reached
URLFormat	Parse extension from url and put it on request context
WithValue	Short-hand middleware to set a key/value on the request context

Extra middlewares & packages

Please see https://github.com/go-chi for additional packages.

package	description
cors	Cross-origin resource sharing (CORS)
docgen	Print chi.Router routes at runtime
jwtauth	JWT authentication
hostrouter	Domain/host based request routing
httplog	Small but powerful structured HTTP request logging
httprate	HTTP request rate limiter
httptracer	HTTP request performance tracing library
httpvcr	Write deterministic tests for external sources
stampede	HTTP request coalescer

context?

context is a tiny pkg that provides simple interface to signal context across call stacks and goroutines. It was originally written by Sameer Ajmani and is available in stdlib since go1.7.

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

and..

Docs: https://golang.org/pkg/context
Source: https://github.com/golang/go/tree/master/src/context

Benchmarks

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

Results as of Jan 9, 2019 with Go 1.11.4 on Linux X1 Carbon laptop

BenchmarkChi_Param            3000000         475 ns/op       432 B/op      3 allocs/op
BenchmarkChi_Param5           2000000         696 ns/op       432 B/op      3 allocs/op
BenchmarkChi_Param20          1000000        1275 ns/op       432 B/op      3 allocs/op
BenchmarkChi_ParamWrite       3000000         505 ns/op       432 B/op      3 allocs/op
BenchmarkChi_GithubStatic     3000000         508 ns/op       432 B/op      3 allocs/op
BenchmarkChi_GithubParam      2000000         669 ns/op       432 B/op      3 allocs/op
BenchmarkChi_GithubAll          10000      134627 ns/op     87699 B/op    609 allocs/op
BenchmarkChi_GPlusStatic      3000000         402 ns/op       432 B/op      3 allocs/op
BenchmarkChi_GPlusParam       3000000         500 ns/op       432 B/op      3 allocs/op
BenchmarkChi_GPlus2Params     3000000         586 ns/op       432 B/op      3 allocs/op
BenchmarkChi_GPlusAll          200000        7237 ns/op      5616 B/op     39 allocs/op
BenchmarkChi_ParseStatic      3000000         408 ns/op       432 B/op      3 allocs/op
BenchmarkChi_ParseParam       3000000         488 ns/op       432 B/op      3 allocs/op
BenchmarkChi_Parse2Params     3000000         551 ns/op       432 B/op      3 allocs/op
BenchmarkChi_ParseAll          100000       13508 ns/op     11232 B/op     78 allocs/op
BenchmarkChi_StaticAll          20000       81933 ns/op     67826 B/op    471 allocs/op

Comparison with other routers: https://gist.github.com/pkieltyka/123032f12052520aaccab752bd3e78cc

NOTE: the allocs in the benchmark above are from the calls to http.Request's WithContext(context.Context) method that clones the http.Request, sets the Context() on the duplicated (alloc'd) request and returns it the new request object. This is just how setting context on a request in Go works.

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

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

Beyond REST

chi is just a http router that lets you decompose request handling into many smaller layers. Many companies use chi to write REST services for their public APIs. But, REST is just a convention for managing state via HTTP, and there's a lot of other pieces required to write a complete client-server system or network of microservices.

Looking beyond REST, I also recommend some newer works in the field:

webrpc - Web-focused RPC client+server framework with code-gen
gRPC - Google's RPC framework via protobufs
graphql - Declarative query language
NATS - lightweight pub-sub

License

Licensed under MIT License

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