# HttpRouter [![Build Status](https://travis-ci.org/julienschmidt/httprouter.png?branch=master)](https://travis-ci.org/julienschmidt/httprouter) [![GoDoc](http://godoc.org/github.com/julienschmidt/httprouter?status.png)](http://godoc.org/github.com/julienschmidt/httprouter)

HttpRouter is a high performance HTTP request router
(also called *multiplexer* or just *mux* for short).

In contrast to the default mux of Go's net/http package, this router supports
variables in the routing pattern and matches against the request method.
It also scales better.

The router is optimized for best performance and a small memory footprint.
It scales well even with very long pathes and a large number of routes.
A compressing dynamic trie (radix tree) structure is used for efficient matching.

## Features
**Zero Garbage:** The matching and dispatching process generates zero bytes of garbage. In fact, the only heap allocations that are made, is by building the map containing the key-value pairs for variables. If the request path contains no variables, not a single heap allocation is necessary.

**Best Performance:** [Benchmarks speak for themselves](https://github.com/julienschmidt/go-http-routing-benchmark). See below for technical details of the implementation.

**Variables in your routing pattern:** Stop parsing the requested URL path, just give the path segment a name and the router delivers the value to you. Because of the design of the router, pattern variables are very cheap.

**Only explicit matches:** With other routers / muxes, like [http.ServeMux](http://golang.org/pkg/net/http/#ServeMux), a requested URL path could match multiple patterns. Therefore they have some awkward pattern priority rules, like *longest match* or *first registered, first matched*. By design of this router, a request can only match exactly one or no route. As a result, there are also no unintended matches, which makes it great for SEO. 

**Stop caring about trailing slashes:** Choose the URL style you like, the router automatically redirects the client if a trailing slash is missing or if there is one extra. Of course it only does so, if the new path has a handler. If you don't like it, you can turn off this behavior.

**No more server crashes:** You can set a PanicHandler to deal with panics occouring during handling a HTTP request. The router then recovers and lets the PanicHandler log what happened and deliver a nice error page.

Of course you can also set a custom NotFound handler and serve files.

## Usage
This is just a quick introduction, view the [GoDoc](http://godoc.org/github.com/julienschmidt/httprouter) for details.

Let's start with a trivial example:
```go
package main

import (
    "fmt"
    "github.com/julienschmidt/httprouter"
    "net/http"
    "log"
)

func Index(w http.ResponseWriter, r *http.Request, _ map[string]string) {
    fmt.Fprint(w, "Welcome!\n")
}

func Hello(w http.ResponseWriter, r *http.Request, vars map[string]string) {
    fmt.Fprintf(w, "hello, %s!\n", vars["name"])
}

func main() {
    router := httprouter.New()
    router.GET("/", Index)
    router.GET("/hello/:name", Hello)

    log.Fatal(http.ListenAndServe(":12345", router))
}
```

### Named parameters
As you can see, `:name` is a *named parameter*.
The values are passed in map, therefore the value of `:name` is available in `vars["name"]`.

Named parameters only match a single path segment:
```
Pattern: /user/:user

 /user/gordon              match
 /user/you                 match
 /user/gordon/profile      no match
 /user/                    no match
```

**Note:** Since this router has only explicit matches, you can not register static routes and paramters for the same path segment. For example you can not register the patterns `/user/new` and `/user/:user` at the same time.

### Catch-All routes
The second type are *catch-all* routes and have the form `*name`. Like the name suggest, they match everything.
Therefore they must always be at the **end** of the pattern:
```
Pattern: /src/*filepath

 /src/                     match
 /src/somefile.go          match
 /src/subdir/somefile.go   match
```

## How does it work?
The router relies on a tree structure which makes heavy use of *common prefixes*, it is basically a *compact* [*prefix tree*](http://en.wikipedia.org/wiki/Trie) (or just [*Radix tree*](http://en.wikipedia.org/wiki/Radix_tree)). Nodes with a common prefix also share a common parent. Here is a short example what the routing tree could look like:

```
Priority   Path             Handles
9          \                map[GET:<1>]
3          ├s               map[]
2          |├earch\         map[GET:<2>, POST:<3>,]
1          |└upport\        map[GET:<4>]
2          ├blog\           map[GET:<5>]
1          |    └:post      map[]
1          |         └\     map[GET:<6>]
2          ├about-us\       map[GET:<7>]
1          |        └team\  map[GET:<8>]
1          └contact\        map[GET:<9>]
```
Every `<num>` represents the memory address of a handler function. If you follow a path trough the tree from the root to the leaf, you get the complete route path, e.g `\search\`, for which a GET- and a POST-handler function are registered.

Since URL pathes have a hierarchical structure and make use only of a limited set of characters, it is very likely that there are a lot of common prefixes. This allows us to easiely reduce the routing into ever smaller problems.

Unlike hash-maps, a tree structure also allows us to use dynamic parts, e.g. the `:post` above, which is just a placeholder for a post name, since we actually match against the routing patterns instead of just comparing hashes. [As benchmarks show](https://github.com/julienschmidt/go-http-routing-benchmark), hash-map based routers also don't scale very well.

For even better scalability, the child nodes on each tree level are ordered by priority, where the priority is just the number of handles registered in sub nodes (children, grandchildren, and so on..).
This helps in two ways:

1. Nodes which are part of the most routing pathes are evaluated first. This helps to make as much routes as possible to be reachable as fast as possible.
2. It is some sort of cost compensation. The longest reachable path (highest cost) can always be evaluated first. The follwing scheme visualizes the tree structure. Nodes are evaluated from top to bottom and from left to right.


```
├------------
├---------
├-----
├----
├--
├--
└-
```

## Where can I find Middleware *X*?
This package just provides a very efficient request router with a few extra features. The router is just a [http.Handler](http://golang.org/pkg/net/http/#Handler), you can chain any http.Handler compatible middleware before the router, for example the [Gorilla handlers](http://www.gorillatoolkit.org/pkg/handlers). Or you could [just write your own](http://justinas.org/writing-http-middleware-in-go/), it's very easy!

Here is a quick example: Does your server serve multiple domains / hosts? You want to use subdomains?
Define a router per host!
```go
// We need an object that implements the http.Handler interface.
// Therefore we need a type for which we implement the ServeHTTP method.
// We just use a map here, in which we map host names to http.Handlers
type HostSwitch map[string]http.Handler

// Implement the ServerHTTP method on our new type
func (hs HostSwitch) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	// Check if a http.Handler is registered for the given host.
	// If yes, use it to handle the request.
	if handler := hs[r.URL.Host]; handler != nil {
		handler.ServeHTTP(w, r)
	}

	// Handle host names for wich no handler is registered
	http.Error(w, "Forbidden", 403) // Or Redirect?
}

func main() {
	// Initialze a router as usual 
    router := httprouter.New()
    router.GET("/", Index)
    router.GET("/hello/:name", Hello)

    // Make a new HostSwitch and insert the router for example.com
    hs := make(HostSwitch)
    hs["example.com"] = router

    // Use the HostSwitch to listen and serve on port 12345
    log.Fatal(http.ListenAndServe(":12345", hs))
}
```