package module
v0.0.0-...-9707327 Latest Latest

This package is not in the latest version of its module.

Go to latest
Published: Feb 7, 2019 License: MIT Imports: 13 Imported by: 0


gocraft/web GoDoc

gocraft/web is a Go mux and middleware package. We deal with casting and reflection so YOUR code can be statically typed. And we're fast.

Getting Started

From your GOPATH:

go get github.com/gocraft/web

Add a file server.go - for instance, src/myapp/server.go

package main

import (

type Context struct {
	HelloCount int

func (c *Context) SetHelloCount(rw web.ResponseWriter, req *web.Request, next web.NextMiddlewareFunc) {
	c.HelloCount = 3
	next(rw, req)

func (c *Context) SayHello(rw web.ResponseWriter, req *web.Request) {
	fmt.Fprint(rw, strings.Repeat("Hello ", c.HelloCount), "World!")

func main() {
	router := web.New(Context{}).                   // Create your router
		Middleware(web.LoggerMiddleware).           // Use some included middleware
		Middleware(web.ShowErrorsMiddleware).       // ...
		Middleware((*Context).SetHelloCount).       // Your own middleware!
		Get("/", (*Context).SayHello)               // Add a route
	http.ListenAndServe("localhost:3000", router)   // Start the server!

Run the server. It will be available on localhost:3000:

go run src/myapp/server.go


  • Super fast and scalable. Added latency is from 3-9μs per request. Routing performance is O(log(N)) in the number of routes.
  • Your own contexts. Easily pass information between your middleware and handler with strong static typing.
  • Easy and powerful routing. Capture path variables. Validate path segments with regexps. Lovely API.
  • Middleware. Middleware can express almost any web-layer feature. We make it easy.
  • Nested routers, contexts, and middleware. Your app has an API, and admin area, and a logged out view. Each view needs different contexts and different middleware. We let you express this hierarchy naturally.
  • Embrace Go's net/http package. Start your server with http.ListenAndServe(), and work directly with http.ResponseWriter and http.Request.
  • Minimal. The core of gocraft/web is lightweight and minimal. Add optional functionality with our built-in middleware, or write your own middleware.


Performance is a first class concern. Every update to this package has its performance measured and tracked in BENCHMARK_RESULTS.

For minimal 'hello world' style apps, added latency is about 3μs. This grows to about 10μs for more complex apps (6 middleware functions, 3 levels of contexts, 150+ routes).

One key design choice we've made is our choice of routing algorithm. Most competing libraries use simple O(N) iteration over all routes to find a match. This is fine if you have only a handful of routes, but starts to break down as your app gets bigger. We use a tree-based router which grows in complexity at O(log(N)).

Application Structure

Making your router

The first thing you need to do is make a new router. Routers serve requests and execute middleware.

router := web.New(YourContext{})
Your context

Wait, what is YourContext{} and why do you need it? It can be any struct you want it to be. Here's an example of one:

type YourContext struct {
  User *User // Assumes you've defined a User type as well

Your context can be empty or it can have various fields in it. The fields can be whatever you want - it's your type! When a new request comes into the router, we'll allocate an instance of this struct and pass it to your middleware and handlers. This allows, for instance, a SetUser middleware to set a User field that can be read in the handlers.

Routes and handlers

Once you have your router, you can add routes to it. Standard HTTP verbs are supported.

router := web.New(YourContext{})
router.Get("/users", (*YourContext).UsersList)
router.Post("/users", (*YourContext).UsersCreate)
router.Put("/users/:id", (*YourContext).UsersUpdate)
router.Delete("/users/:id", (*YourContext).UsersDelete)
router.Patch("/users/:id", (*YourContext).UsersUpdate)
router.Get("/", (*YourContext).Root)

What is that funny (*YourContext).Root notation? It's called a method expression. It lets your handlers look like this:

func (c *YourContext) Root(rw web.ResponseWriter, req *web.Request) {
	if c.User != nil {
		fmt.Fprint(rw, "Hello,", c.User.Name)
	} else {
		fmt.Fprint(rw, "Hello, anonymous person")

All method expressions do is return a function that accepts the type as the first argument. So your handler can also look like this:

func Root(c *YourContext, rw web.ResponseWriter, req *web.Request) {}

Of course, if you don't need a context for a particular action, you can also do that:

func Root(rw web.ResponseWriter, req *web.Request) {}

Note that handlers always need to accept two input parameters: web.ResponseWriter, and *web.Request, both of which wrap the standard http.ResponseWriter and *http.Request, respectively.


You can add middleware to a router:

router := web.New(YourContext{})
// add routes, more middleware

This is what a middleware handler looks like:

func (c *YourContext) UserRequired(rw web.ResponseWriter, r *web.Request, next web.NextMiddlewareFunc) {
	user := userFromSession(r)  // Pretend like this is defined. It reads a session cookie and returns a *User or nil.
	if user != nil {
		c.User = user
		next(rw, r)
	} else {
		rw.Header().Set("Location", "/")
		// do NOT call next()

Some things to note about the above example:

  • We set fields in the context for future middleware / handlers to use.
  • We can call next(), or not. Not calling next() effectively stops the middleware stack.

Of course, generic middleware without contexts is supported:

func GenericMiddleware(rw web.ResponseWriter, r *web.Request, next web.NextMiddlewareFunc) {
	// ...
Nested routers

Nested routers let you run different middleware and use different contexts for different parts of your app. Some common scenarios:

  • You want to run an AdminRequired middleware on all your admin routes, but not on API routes. Your context needs a CurrentAdmin field.
  • You want to run an OAuth middleware on your API routes. Your context needs an AccessToken field.
  • You want to run session handling middleware on ALL your routes. Your context needs a Session field.

Let's implement that. Your contexts would look like this:

type Context struct {
	Session map[string]string

type AdminContext struct {
	CurrentAdmin *User

type ApiContext struct {
	AccessToken string

Note that we embed a pointer to the parent context in each subcontext. This is required.

Now that we have our contexts, let's create our routers:

rootRouter := web.New(Context{})

apiRouter := rootRouter.Subrouter(ApiContext{}, "/api")
apiRouter.Get("/tickets", (*ApiContext).TicketsIndex)

adminRouter := rootRouter.Subrouter(AdminContext{}, "/admin")

// Given the path namesapce for this router is "/admin", the full path of this route is "/admin/reports"
adminRouter.Get("/reports", (*AdminContext).Reports)

Note that each time we make a subrouter, we need to supply the context as well as a path namespace. The context CAN be the same as the parent context, and the namespace CAN just be "/" for no namespace.

Request lifecycle

The following is a detailed account of the request lifecycle:

  1. A request comes in. Yay! (follow along in router_serve.go if you'd like)
  2. Wrap the default Go http.ResponseWriter and http.Request in a web.ResponseWriter and web.Request, respectively (via structure embedding).
  3. Allocate a new root context. This context is passed into your root middleware.
  4. Execute middleware on the root router. We do this before we find a route!
  5. After all of the root router's middleware is executed, we'll run a 'virtual' routing middleware that determines the target route.
    • If the there's no route found, we'll execute the NotFound handler if supplied. Otherwise, we'll write a 404 response and start unwinding the root middlware.
  6. Now that we have a target route, we can allocate the context tree of the target router.
  7. Start executing middleware on the nested middleware leading up to the final router/route.
  8. After all middleware is executed, we'll run another 'virtual' middleware that invokes the final handler corresponding to the target route.
  9. Unwind all middleware calls (if there's any code after next() in the middleware, obviously that's going to run at some point).
Capturing path params; regexp conditions

You can capture path variables like this:


In your handler, you can access them like this:

func (c *YourContext) Root(rw web.ResponseWriter, req *web.Request) {
	fmt.Fprint(rw, "Suggestion ID:", req.PathParams["suggestion_id"])
	fmt.Fprint(rw, "Comment ID:", req.PathParams["comment_id"])

You can also validate the format of your path params with a regexp. For instance, to ensure the 'ids' start with a digit:


You can match any route past a certain point like this:


The path params will contain a “” member with the rest of your path. It is illegal to add any more paths past the “” path param, as it’s meant to match every path afterwards, in all cases.

For Example: /suggestions/123/comments/321/foo/879/bar/834

Elicits path params: * “suggestion_id”: 123, * “comment_id”: 321, * “*”: “foo/879/bar/834”

One thing you CANNOT currently do is use regexps outside of a path segment. For instance, optional path segments are not supported - you would have to define multiple routes that both point to the same handler. This design decision was made to enable efficient routing.

Not Found handlers

If a route isn't found, by default we'll return a 404 status and render the text "Not Found".

You can supply a custom NotFound handler on your root router:


Your handler can optionally accept a pointer to the root context. NotFound handlers look like this:

func (c *Context) NotFound(rw web.ResponseWriter, r *web.Request) {
	rw.WriteHeader(http.StatusNotFound) // You probably want to return 404. But you can also redirect or do whatever you want.
	fmt.Fprintf(rw, "My Not Found")     // Render you own HTML or something!
OPTIONS handlers

If an OPTIONS request is made and routes with other methods are found for the requested path, then by default we'll return an empty response with an appropriate Access-Control-Allow-Methods header.

You can supply a custom OPTIONS handler on your root router:


Your handler can optionally accept a pointer to the root context. OPTIONS handlers look like this:

func (c *Context) OptionsHandler(rw web.ResponseWriter, r *web.Request, methods []string) {
	rw.Header().Add("Access-Control-Allow-Methods", strings.Join(methods, ", "))
	rw.Header().Add("Access-Control-Allow-Origin", "*")
Error handlers

By default, if there's a panic in middleware or a handler, we'll return a 500 status and render the text "Application Error".

If you use the included middleware web.ShowErrorsMiddleware, a panic will result in a pretty backtrace being rendered in HTML. This is great for development.

You can also supply a custom Error handler on any router (not just the root router):


Your handler can optionally accept a pointer to its corresponding context. Error handlers look like this:

func (c *Context) Error(rw web.ResponseWriter, r *web.Request, err interface{}) {
	fmt.Fprint(w, "Error", err)
Included middleware

We ship with three basic pieces of middleware: a logger, an exception printer, and a static file server. To use them:

router := web.New(Context{})

// The static middleware serves files. Examples:
// "GET /" will serve an index file at pwd/public/index.html
// "GET /robots.txt" will serve the file at pwd/public/robots.txt
// "GET /images/foo.gif" will serve the file at pwd/public/images/foo.gif
currentRoot, _ := os.Getwd()
router.Middleware(web.StaticMiddleware(path.Join(currentRoot, "public"), web.StaticOption{IndexFile: "index.html"}))

NOTE: You might not want to use web.ShowErrorsMiddleware in production. You can easily do something like this:

router := web.New(Context{})
if MyEnvironment == "development" {
// ...
Starting your server

Since web.Router implements http.Handler (eg, ServeHTTP(ResponseWriter, *Request)), you can easily plug it in to the standard Go http machinery:

router := web.New(Context{})
// ... Add routes and such.
http.ListenAndServe("localhost:8080", router)
Rendering responses

So now you routed a request to a handler. You have a web.ResponseWriter (http.ResponseWriter) and web.Request (http.Request). Now what?

// You can print to the ResponseWriter!
fmt.Fprintf(rw, "<html>I'm a web page!</html>")

This is currently where the implementation of this library stops. I recommend you read the documentation of net/http.

Extra Middlware

This package is going to keep the built-in middlware simple and lean. Extra middleware can be found across the web:

If you'd like me to link to your middleware, let me know with a pull request to this README.


gocraft offers a toolkit for building web apps. Currently these packages are available:

  • gocraft/web - Go Router + Middleware. Your Contexts.
  • gocraft/dbr - Additions to Go's database/sql for super fast performance and convenience.
  • gocraft/health - Instrument your web apps with logging and metrics.
  • gocraft/work - Process background jobs in Go.

These packages were developed by the engineering team at UserVoice and currently power much of its infrastructure and tech stack.

Thanks & Authors

I use code/got inspiration from these excellent libraries:





This section is empty.


View Source
var DefaultNotFoundResponse = "Not Found"

DefaultNotFoundResponse is the default text rendered when no route is found and no NotFound handlers are present.

View Source
var DefaultPanicResponse = "Application Error"

DefaultPanicResponse is the default text rendered when a panic occurs and no Error handlers are present.

View Source
var Logger = log.New(os.Stdout, "", 0)

Logger can be set to your own logger. Logger only applies to the LoggerMiddleware.

View Source
var PanicHandler = PanicReporter(logPanicReporter{
	log: log.New(os.Stderr, "ERROR ", log.Ldate|log.Ltime|log.Lmicroseconds|log.Lshortfile),

PanicHandler will be logged to in panic conditions (eg, division by zero in an app handler). Applications can set web.PanicHandler = your own logger, if they wish. In terms of logging the requests / responses, see logger_middleware. That is a completely separate system.


func LoggerMiddleware

func LoggerMiddleware(rw ResponseWriter, req *Request, next NextMiddlewareFunc)

LoggerMiddleware is generic middleware that will log requests to Logger (by default, Stdout).

func ShowErrorsMiddleware

func ShowErrorsMiddleware(rw ResponseWriter, req *Request, next NextMiddlewareFunc)

ShowErrorsMiddleware will catch panics and render an HTML page with the stack trace. This middleware should only be used in development.

func StaticMiddleware

func StaticMiddleware(path string, option ...StaticOption) func(ResponseWriter, *Request, NextMiddlewareFunc)

StaticMiddleware is the same as StaticMiddlewareFromDir, but accepts a path string for backwards compatibility.

func StaticMiddlewareFromDir

func StaticMiddlewareFromDir(dir http.FileSystem, options ...StaticOption) func(ResponseWriter, *Request, NextMiddlewareFunc)

StaticMiddlewareFromDir returns a middleware that serves static files from the specified http.FileSystem. This middleware is great for development because each file is read from disk each time and no special caching or cache headers are sent.

If a path is requested which maps to a folder with an index.html folder on your filesystem, then that index.html file will be served.


type GenericHandler

type GenericHandler func(ResponseWriter, *Request)

GenericHandler are handlers that don't have or need a context. If your handler doesn't need a context, you can use this signature to get a small performance boost.

type GenericMiddleware

type GenericMiddleware func(ResponseWriter, *Request, NextMiddlewareFunc)

GenericMiddleware are middleware that doesn't have or need a context. General purpose middleware, such as static file serving, has this signature. If your middlware doesn't need a context, you can use this signature to get a small performance boost.

type NextMiddlewareFunc

type NextMiddlewareFunc func(ResponseWriter, *Request)

NextMiddlewareFunc are functions passed into your middleware. To advance the middleware, call the function. You should usually pass the existing ResponseWriter and *Request into the next middlware, but you can chose to swap them if you want to modify values or capture things written to the ResponseWriter.

type PanicReporter

type PanicReporter interface {
	// Panic is called with the URL of the request, the result of calling recover, and the stack.
	Panic(url string, err interface{}, stack string)

PanicReporter can receive panics that happen when serving a request and report them to a log of some sort.

type Request

type Request struct {

	// PathParams exists if you have wildcards in your URL that you need to capture.
	// Eg, /users/:id/tickets/:ticket_id and /users/1/tickets/33 would yield the map {id: "3", ticket_id: "33"}
	PathParams map[string]string
	// contains filtered or unexported fields

Request wraps net/http's Request and gocraf/web specific fields. In particular, PathParams is used to access captures params in your URL. A Request is sent to handlers on each request.

func (*Request) IsRouted

func (r *Request) IsRouted() bool

IsRouted can be called from middleware to determine if the request has been routed yet.

func (*Request) RoutePath

func (r *Request) RoutePath() string

RoutePath returns the routed path string. Eg, if a route was registered with router.Get("/suggestions/:suggestion_id/comments", f), then RoutePath will return "/suggestions/:suggestion_id/comments".

type ResponseWriter

type ResponseWriter interface {

	// StatusCode returns the written status code, or 0 if none has been written yet.
	StatusCode() int
	// Written returns whether the header has been written yet.
	Written() bool
	// Size returns the size in bytes of the body written so far.
	Size() int

ResponseWriter includes net/http's ResponseWriter and adds a StatusCode() method to obtain the written status code. A ResponseWriter is sent to handlers on each request.

type Router

type Router struct {
	// contains filtered or unexported fields

Router implements net/http's Handler interface and is what you attach middleware, routes/handlers, and subrouters to.

func New

func New(ctx interface{}) *Router

New returns a new router with context type ctx. ctx should be a struct instance, whose purpose is to communicate type information. On each request, an instance of this context type will be automatically allocated and sent to handlers.

func NewWithPrefix

func NewWithPrefix(ctx interface{}, pathPrefix string) *Router

NewWithPrefix returns a new router (see New) but each route will have an implicit prefix. For instance, with pathPrefix = "/api/v2", all routes under this router will begin with "/api/v2".

func (*Router) Delete

func (r *Router) Delete(path string, fn interface{}) *Router

Delete will add a route to the router that matches on DELETE requests and the specified path.

func (*Router) Error

func (r *Router) Error(fn interface{}) *Router

Error sets the specified function as the error handler (when panics happen) and returns the router.

func (*Router) Get

func (r *Router) Get(path string, fn interface{}) *Router

Get will add a route to the router that matches on GET requests and the specified path.

func (*Router) Head

func (r *Router) Head(path string, fn interface{}) *Router

Head will add a route to the router that matches on HEAD requests and the specified path.

func (*Router) Middleware

func (r *Router) Middleware(fn interface{}) *Router

Middleware adds the specified middleware tot he router and returns the router.

func (*Router) NotFound

func (r *Router) NotFound(fn interface{}) *Router

NotFound sets the specified function as the not-found handler (when no route matches) and returns the router. Note that only the root router can have a NotFound handler.

func (*Router) Options

func (r *Router) Options(path string, fn interface{}) *Router

Options will add a route to the router that matches on OPTIONS requests and the specified path.

func (*Router) OptionsHandler

func (r *Router) OptionsHandler(fn interface{}) *Router

OptionsHandler sets the specified function as the options handler and returns the router. Note that only the root router can have a OptionsHandler handler.

func (*Router) Patch

func (r *Router) Patch(path string, fn interface{}) *Router

Patch will add a route to the router that matches on PATCH requests and the specified path.

func (*Router) Post

func (r *Router) Post(path string, fn interface{}) *Router

Post will add a route to the router that matches on POST requests and the specified path.

func (*Router) Put

func (r *Router) Put(path string, fn interface{}) *Router

Put will add a route to the router that matches on PUT requests and the specified path.

func (*Router) ServeHTTP

func (rootRouter *Router) ServeHTTP(rw http.ResponseWriter, r *http.Request)

This is the entry point for servering all requests.

func (*Router) Subrouter

func (r *Router) Subrouter(ctx interface{}, pathPrefix string) *Router

Subrouter attaches a new subrouter to the specified router and returns it. You can use the same context or pass a new one. If you pass a new one, it must embed a pointer to the previous context in the first slot. You can also pass a pathPrefix that each route will have. If "" is passed, then no path prefix is applied.

type StaticOption

type StaticOption struct {
	Prefix    string
	IndexFile string

StaticOption configures how StaticMiddlewareDir handles url paths and index files for directories. If set, Prefix is removed from the start of the url path before attempting to serve a directory or file. If set, IndexFile is the index file to serve when the url path maps to a directory.

Jump to

Keyboard shortcuts

? : This menu
/ : Search site
f or F : Jump to
y or Y : Canonical URL