elb-instance-status/vendor/github.com/gorilla/mux/README.md

mux
===
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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:

	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:

	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():

	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:

	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:

	r.PathPrefix("/products/")

...or HTTP methods:

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

...or URL schemes:

	r.Schemes("https")

...or header values:

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

...or query values:

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

...or to use a custom matcher function:

	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:

	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:

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

Then register routes in the subrouter:

	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:

	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:

	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:

	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:

	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:

	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:

	// "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:

	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.