mirror of https://github.com/prometheus/prometheus
324 lines
14 KiB
Markdown
324 lines
14 KiB
Markdown
# HttpRouter [](https://travis-ci.org/julienschmidt/httprouter) [](http://gocover.io/github.com/julienschmidt/httprouter) [](http://godoc.org/github.com/julienschmidt/httprouter)
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HttpRouter is a lightweight high performance HTTP request router
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(also called *multiplexer* or just *mux* for short) for [Go](http://golang.org/).
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In contrast to the [default mux](http://golang.org/pkg/net/http/#ServeMux) of Go's net/http package, this router supports
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variables in the routing pattern and matches against the request method.
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It also scales better.
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The router is optimized for high performance and a small memory footprint.
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It scales well even with very long paths and a large number of routes.
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A compressing dynamic trie (radix tree) structure is used for efficient matching.
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## Features
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**Only explicit matches:** With other routers, like [http.ServeMux](http://golang.org/pkg/net/http/#ServeMux),
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a requested URL path could match multiple patterns. Therefore they have some
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awkward pattern priority rules, like *longest match* or *first registered,
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first matched*. By design of this router, a request can only match exactly one
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or no route. As a result, there are also no unintended matches, which makes it
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great for SEO and improves the user experience.
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**Stop caring about trailing slashes:** Choose the URL style you like, the
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router automatically redirects the client if a trailing slash is missing or if
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there is one extra. Of course it only does so, if the new path has a handler.
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If you don't like it, you can [turn off this behavior](http://godoc.org/github.com/julienschmidt/httprouter#Router.RedirectTrailingSlash).
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**Path auto-correction:** Besides detecting the missing or additional trailing
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slash at no extra cost, the router can also fix wrong cases and remove
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superfluous path elements (like `../` or `//`).
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Is [CAPTAIN CAPS LOCK](http://www.urbandictionary.com/define.php?term=Captain+Caps+Lock) one of your users?
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HttpRouter can help him by making a case-insensitive look-up and redirecting him
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to the correct URL.
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**Parameters in your routing pattern:** Stop parsing the requested URL path,
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just give the path segment a name and the router delivers the dynamic value to
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you. Because of the design of the router, path parameters are very cheap.
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**Zero Garbage:** The matching and dispatching process generates zero bytes of
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garbage. In fact, the only heap allocations that are made, is by building the
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slice of the key-value pairs for path parameters. If the request path contains
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no parameters, not a single heap allocation is necessary.
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**Best Performance:** [Benchmarks speak for themselves](https://github.com/julienschmidt/go-http-routing-benchmark).
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See below for technical details of the implementation.
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**No more server crashes:** You can set a [Panic handler](http://godoc.org/github.com/julienschmidt/httprouter#Router.PanicHandler) to deal with panics
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occurring during handling a HTTP request. The router then recovers and lets the
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PanicHandler log what happened and deliver a nice error page.
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Of course you can also set **custom [NotFound](http://godoc.org/github.com/julienschmidt/httprouter#Router.NotFound) and [MethodNotAllowed](http://godoc.org/github.com/julienschmidt/httprouter#Router.MethodNotAllowed) handlers** and [**serve static files**](http://godoc.org/github.com/julienschmidt/httprouter#Router.ServeFiles).
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## Usage
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This is just a quick introduction, view the [GoDoc](http://godoc.org/github.com/julienschmidt/httprouter) for details.
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Let's start with a trivial example:
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```go
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package main
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import (
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"fmt"
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"github.com/julienschmidt/httprouter"
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"net/http"
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"log"
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)
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func Index(w http.ResponseWriter, r *http.Request, _ httprouter.Params) {
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fmt.Fprint(w, "Welcome!\n")
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}
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func Hello(w http.ResponseWriter, r *http.Request, ps httprouter.Params) {
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fmt.Fprintf(w, "hello, %s!\n", ps.ByName("name"))
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}
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func main() {
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router := httprouter.New()
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router.GET("/", Index)
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router.GET("/hello/:name", Hello)
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log.Fatal(http.ListenAndServe(":8080", router))
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}
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```
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### Named parameters
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As you can see, `:name` is a *named parameter*.
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The values are accessible via `httprouter.Params`, which is just a slice of `httprouter.Param`s.
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You can get the value of a parameter either by its index in the slice, or by using the `ByName(name)` method:
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`:name` can be retrived by `ByName("name")`.
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Named parameters only match a single path segment:
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```
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Pattern: /user/:user
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/user/gordon match
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/user/you match
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/user/gordon/profile no match
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/user/ no match
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```
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**Note:** Since this router has only explicit matches, you can not register static routes and parameters for the same path segment. For example you can not register the patterns `/user/new` and `/user/:user` for the same request method at the same time. The routing of different request methods is independent from each other.
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### Catch-All parameters
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The second type are *catch-all* parameters and have the form `*name`.
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Like the name suggests, they match everything.
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Therefore they must always be at the **end** of the pattern:
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```
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Pattern: /src/*filepath
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/src/ match
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/src/somefile.go match
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/src/subdir/somefile.go match
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```
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## How does it work?
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The router relies on a tree structure which makes heavy use of *common prefixes*,
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it is basically a *compact* [*prefix tree*](http://en.wikipedia.org/wiki/Trie)
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(or just [*Radix tree*](http://en.wikipedia.org/wiki/Radix_tree)).
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Nodes with a common prefix also share a common parent. Here is a short example
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what the routing tree for the `GET` request method could look like:
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```
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Priority Path Handle
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9 \ *<1>
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3 ├s nil
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2 |├earch\ *<2>
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1 |└upport\ *<3>
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2 ├blog\ *<4>
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1 | └:post nil
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1 | └\ *<5>
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2 ├about-us\ *<6>
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1 | └team\ *<7>
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1 └contact\ *<8>
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```
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Every `*<num>` represents the memory address of a handler function (a pointer).
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If you follow a path trough the tree from the root to the leaf, you get the
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complete route path, e.g `\blog\:post\`, where `:post` is just a placeholder
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([*parameter*](#named-parameters)) for an actual post name. Unlike hash-maps, a
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tree structure also allows us to use dynamic parts like the `:post` parameter,
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since we actually match against the routing patterns instead of just comparing
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hashes. [As benchmarks show](https://github.com/julienschmidt/go-http-routing-benchmark),
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this works very well and efficient.
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Since URL paths have a hierarchical structure and make use only of a limited set
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of characters (byte values), it is very likely that there are a lot of common
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prefixes. This allows us to easily reduce the routing into ever smaller problems.
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Moreover the router manages a separate tree for every request method.
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For one thing it is more space efficient than holding a method->handle map in
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every single node, for another thing is also allows us to greatly reduce the
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routing problem before even starting the look-up in the prefix-tree.
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For even better scalability, the child nodes on each tree level are ordered by
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priority, where the priority is just the number of handles registered in sub
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nodes (children, grandchildren, and so on..).
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This helps in two ways:
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1. Nodes which are part of the most routing paths are evaluated first. This
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helps to make as much routes as possible to be reachable as fast as possible.
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2. It is some sort of cost compensation. The longest reachable path (highest
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cost) can always be evaluated first. The following scheme visualizes the tree
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structure. Nodes are evaluated from top to bottom and from left to right.
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```
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├------------
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├---------
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├-----
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├----
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├--
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├--
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└-
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```
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## Why doesn't this work with http.Handler?
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**It does!** The router itself implements the http.Handler interface.
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Moreover the router provides convenient [adapters for http.Handler](http://godoc.org/github.com/julienschmidt/httprouter#Router.Handler)s and [http.HandlerFunc](http://godoc.org/github.com/julienschmidt/httprouter#Router.HandlerFunc)s
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which allows them to be used as a [httprouter.Handle](http://godoc.org/github.com/julienschmidt/httprouter#Router.Handle) when registering a route.
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The only disadvantage is, that no parameter values can be retrieved when a
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http.Handler or http.HandlerFunc is used, since there is no efficient way to
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pass the values with the existing function parameters.
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Therefore [httprouter.Handle](http://godoc.org/github.com/julienschmidt/httprouter#Router.Handle) has a third function parameter.
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Just try it out for yourself, the usage of HttpRouter is very straightforward. The package is compact and minimalistic, but also probably one of the easiest routers to set up.
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## Where can I find Middleware *X*?
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This package just provides a very efficient request router with a few extra
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features. The router is just a [http.Handler](http://golang.org/pkg/net/http/#Handler),
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you can chain any http.Handler compatible middleware before the router,
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for example the [Gorilla handlers](http://www.gorillatoolkit.org/pkg/handlers).
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Or you could [just write your own](http://justinas.org/writing-http-middleware-in-go/),
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it's very easy!
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Alternatively, you could try [a web framework based on HttpRouter](#web-frameworks-based-on-httprouter).
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### Multi-domain / Sub-domains
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Here is a quick example: Does your server serve multiple domains / hosts?
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You want to use sub-domains?
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Define a router per host!
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```go
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// We need an object that implements the http.Handler interface.
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// Therefore we need a type for which we implement the ServeHTTP method.
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// We just use a map here, in which we map host names (with port) to http.Handlers
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type HostSwitch map[string]http.Handler
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// Implement the ServerHTTP method on our new type
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func (hs HostSwitch) ServeHTTP(w http.ResponseWriter, r *http.Request) {
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// Check if a http.Handler is registered for the given host.
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// If yes, use it to handle the request.
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if handler := hs[r.Host]; handler != nil {
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handler.ServeHTTP(w, r)
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} else {
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// Handle host names for wich no handler is registered
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http.Error(w, "Forbidden", 403) // Or Redirect?
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}
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}
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func main() {
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// Initialize a router as usual
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router := httprouter.New()
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router.GET("/", Index)
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router.GET("/hello/:name", Hello)
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// Make a new HostSwitch and insert the router (our http handler)
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// for example.com and port 12345
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hs := make(HostSwitch)
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hs["example.com:12345"] = router
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// Use the HostSwitch to listen and serve on port 12345
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log.Fatal(http.ListenAndServe(":12345", hs))
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}
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```
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### Basic Authentication
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Another quick example: Basic Authentification (RFC 2617) for handles:
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```go
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package main
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import (
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"bytes"
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"encoding/base64"
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"fmt"
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"github.com/julienschmidt/httprouter"
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"net/http"
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"log"
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"strings"
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)
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func BasicAuth(h httprouter.Handle, user, pass []byte) httprouter.Handle {
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return func(w http.ResponseWriter, r *http.Request, ps httprouter.Params) {
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const basicAuthPrefix string = "Basic "
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// Get the Basic Authentication credentials
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auth := r.Header.Get("Authorization")
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if strings.HasPrefix(auth, basicAuthPrefix) {
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// Check credentials
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payload, err := base64.StdEncoding.DecodeString(auth[len(basicAuthPrefix):])
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if err == nil {
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pair := bytes.SplitN(payload, []byte(":"), 2)
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if len(pair) == 2 &&
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bytes.Equal(pair[0], user) &&
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bytes.Equal(pair[1], pass) {
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// Delegate request to the given handle
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h(w, r, ps)
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return
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}
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}
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}
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// Request Basic Authentication otherwise
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w.Header().Set("WWW-Authenticate", "Basic realm=Restricted")
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http.Error(w, http.StatusText(http.StatusUnauthorized), http.StatusUnauthorized)
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}
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}
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func Index(w http.ResponseWriter, r *http.Request, _ httprouter.Params) {
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fmt.Fprint(w, "Not protected!\n")
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}
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func Protected(w http.ResponseWriter, r *http.Request, _ httprouter.Params) {
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fmt.Fprint(w, "Protected!\n")
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}
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func main() {
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user := []byte("gordon")
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pass := []byte("secret!")
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router := httprouter.New()
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router.GET("/", Index)
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router.GET("/protected/", BasicAuth(Protected, user, pass))
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log.Fatal(http.ListenAndServe(":8080", router))
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}
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```
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## Chaining with the NotFound handler
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**NOTE: It might be required to set [Router.HandleMethodNotAllowed](http://godoc.org/github.com/julienschmidt/httprouter#Router.HandleMethodNotAllowed) to `false` to avoid problems.**
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You can use another [http.Handler](http://golang.org/pkg/net/http/#Handler), for example another router, to handle requests which could not be matched by this router by using the [Router.NotFound](http://godoc.org/github.com/julienschmidt/httprouter#Router.NotFound) handler. This allows chaining.
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### Static files
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The `NotFound` handler can for example be used to serve static files from the root path `/` (like an index.html file along with other assets):
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```go
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// Serve static files from the ./public directory
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router.NotFound = http.FileServer(http.Dir("public")).ServeHTTP
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```
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But this approach sidesteps the strict core rules of this router to avoid routing problems. A cleaner approach is to use a distinct sub-path for serving files, like `/static/*filepath` or `/files/*filepath`.
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## Web Frameworks based on HttpRouter
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If the HttpRouter is a bit too minimalistic for you, you might try one of the following more high-level 3rd-party web frameworks building upon the HttpRouter package:
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* [Ace](https://github.com/plimble/ace): Blazing fast Go Web Framework
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* [api2go](https://github.com/univedo/api2go): A JSON API Implementation for Go
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* [Gin](https://github.com/gin-gonic/gin): Features a martini-like API with much better performance
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* [Goat](https://github.com/bahlo/goat): A minimalistic REST API server in Go
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* [Hikaru](https://github.com/najeira/hikaru): Supports standalone and Google AppEngine
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* [Hitch](https://github.com/nbio/hitch): Hitch ties httprouter, [httpcontext](https://github.com/nbio/httpcontext), and middleware up in a bow
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* [kami](https://github.com/guregu/kami): A tiny web framework using x/net/context
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* [Medeina](https://github.com/imdario/medeina): Inspired by Ruby's Roda and Cuba
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* [Neko](https://github.com/rocwong/neko): A lightweight web application framework for Golang
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* [Roxanna](https://github.com/iamthemuffinman/Roxanna): An amalgamation of httprouter, better logging, and hot reload
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* [siesta](https://github.com/VividCortex/siesta): Composable HTTP handlers with contexts
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