mux
===
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http://www.gorillatoolkit.org/pkg/mux

Package `gorilla/mux` implements a request router and dispatcher.

The name mux stands for "HTTP request multiplexer". Like the standard `http.ServeMux`, `mux.Router` matches incoming requests against a list of registered routes and calls a handler for the route that matches the URL or other conditions. The main features are:

* Requests can be matched based on URL host, path, path prefix, schemes, header and query values, HTTP methods or using custom matchers.
* URL hosts and paths can have variables with an optional regular expression.
* Registered URLs can be built, or "reversed", which helps maintaining references to resources.
* Routes can be used as subrouters: nested routes are only tested if the parent route matches. This is useful to define groups of routes that share common conditions like a host, a path prefix or other repeated attributes. As a bonus, this optimizes request matching.
* It implements the `http.Handler` interface so it is compatible with the standard `http.ServeMux`.

Let's start registering a couple of URL paths and handlers:

```go
func main() {
	r := mux.NewRouter()
	r.HandleFunc("/", HomeHandler)
	r.HandleFunc("/products", ProductsHandler)
	r.HandleFunc("/articles", ArticlesHandler)
	http.Handle("/", r)
}
```

Here we register three routes mapping URL paths to handlers. This is equivalent to how `http.HandleFunc()` works: if an incoming request URL matches one of the paths, the corresponding handler is called passing (`http.ResponseWriter`, `*http.Request`) as parameters.

Paths can have variables. They are defined using the format `{name}` or `{name:pattern}`. If a regular expression pattern is not defined, the matched variable will be anything until the next slash. For example:

```go
r := mux.NewRouter()
r.HandleFunc("/products/{key}", ProductHandler)
r.HandleFunc("/articles/{category}/", ArticlesCategoryHandler)
r.HandleFunc("/articles/{category}/{id:[0-9]+}", ArticleHandler)
```

The names are used to create a map of route variables which can be retrieved calling `mux.Vars()`:

```go
vars := mux.Vars(request)
category := vars["category"]
```

And this is all you need to know about the basic usage. More advanced options are explained below.

Routes can also be restricted to a domain or subdomain. Just define a host pattern to be matched. They can also have variables:

```go
r := mux.NewRouter()
// Only matches if domain is "www.example.com".
r.Host("www.example.com")
// Matches a dynamic subdomain.
r.Host("{subdomain:[a-z]+}.domain.com")
```

There are several other matchers that can be added. To match path prefixes:

```go
r.PathPrefix("/products/")
```

...or HTTP methods:

```go
r.Methods("GET", "POST")
```

...or URL schemes:

```go
r.Schemes("https")
```

...or header values:

```go
r.Headers("X-Requested-With", "XMLHttpRequest")
```

...or query values:

```go
r.Queries("key", "value")
```

...or to use a custom matcher function:

```go
r.MatcherFunc(func(r *http.Request, rm *RouteMatch) bool {
	return r.ProtoMajor == 0
})
```

...and finally, it is possible to combine several matchers in a single route:

```go
r.HandleFunc("/products", ProductsHandler).
  Host("www.example.com").
  Methods("GET").
  Schemes("http")
```

Setting the same matching conditions again and again can be boring, so we have a way to group several routes that share the same requirements. We call it "subrouting".

For example, let's say we have several URLs that should only match when the host is `www.example.com`. Create a route for that host and get a "subrouter" from it:

```go
r := mux.NewRouter()
s := r.Host("www.example.com").Subrouter()
```

Then register routes in the subrouter:

```go
s.HandleFunc("/products/", ProductsHandler)
s.HandleFunc("/products/{key}", ProductHandler)
s.HandleFunc("/articles/{category}/{id:[0-9]+}"), ArticleHandler)
```

The three URL paths we registered above will only be tested if the domain is `www.example.com`, because the subrouter is tested first. This is not only convenient, but also optimizes request matching. You can create subrouters combining any attribute matchers accepted by a route.

Subrouters can be used to create domain or path "namespaces": you define subrouters in a central place and then parts of the app can register its paths relatively to a given subrouter.

There's one more thing about subroutes. When a subrouter has a path prefix, the inner routes use it as base for their paths:

```go
r := mux.NewRouter()
s := r.PathPrefix("/products").Subrouter()
// "/products/"
s.HandleFunc("/", ProductsHandler)
// "/products/{key}/"
s.HandleFunc("/{key}/", ProductHandler)
// "/products/{key}/details"
s.HandleFunc("/{key}/details", ProductDetailsHandler)
```

Now let's see how to build registered URLs.

Routes can be named. All routes that define a name can have their URLs built, or "reversed". We define a name calling `Name()` on a route. For example:

```go
r := mux.NewRouter()
r.HandleFunc("/articles/{category}/{id:[0-9]+}", ArticleHandler).
  Name("article")
```

To build a URL, get the route and call the `URL()` method, passing a sequence of key/value pairs for the route variables. For the previous route, we would do:

```go
url, err := r.Get("article").URL("category", "technology", "id", "42")
```

...and the result will be a `url.URL` with the following path:

```
"/articles/technology/42"
```

This also works for host variables:

```go
r := mux.NewRouter()
r.Host("{subdomain}.domain.com").
  Path("/articles/{category}/{id:[0-9]+}").
  HandlerFunc(ArticleHandler).
  Name("article")

// url.String() will be "http://news.domain.com/articles/technology/42"
url, err := r.Get("article").URL("subdomain", "news",
                                 "category", "technology",
                                 "id", "42")
```

All variables defined in the route are required, and their values must conform to the corresponding patterns. These requirements guarantee that a generated URL will always match a registered route -- the only exception is for explicitly defined "build-only" routes which never match.

Regex support also exists for matching Headers within a route. For example, we could do:

```go
r.HeadersRegexp("Content-Type", "application/(text|json)")
```

...and the route will match both requests with a Content-Type of `application/json` as well as `application/text`

There's also a way to build only the URL host or path for a route: use the methods `URLHost()` or `URLPath()` instead. For the previous route, we would do:

```go
// "http://news.domain.com/"
host, err := r.Get("article").URLHost("subdomain", "news")

// "/articles/technology/42"
path, err := r.Get("article").URLPath("category", "technology", "id", "42")
```

And if you use subrouters, host and path defined separately can be built as well:

```go
r := mux.NewRouter()
s := r.Host("{subdomain}.domain.com").Subrouter()
s.Path("/articles/{category}/{id:[0-9]+}").
  HandlerFunc(ArticleHandler).
  Name("article")

// "http://news.domain.com/articles/technology/42"
url, err := r.Get("article").URL("subdomain", "news",
                                 "category", "technology",
                                 "id", "42")
```

## Full Example

Here's a complete, runnable example of a small `mux` based server:

```go
package main

import (
	"net/http"

	"github.com/gorilla/mux"
)

func YourHandler(w http.ResponseWriter, r *http.Request) {
	w.Write([]byte("Gorilla!\n"))
}

func main() {
	r := mux.NewRouter()
	// Routes consist of a path and a handler function.
	r.HandleFunc("/", YourHandler)

	// Bind to a port and pass our router in
	http.ListenAndServe(":8000", r)
}
```

## License

BSD licensed. See the LICENSE file for details.