【服务计算】gorilla/mux源码分析

0、gorilla/mux

Package gorilla/mux implements a request router and dispatcher for matching incoming requests to their respective handler.

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:

• It implements the http.Handler interface so it is compatible with the standard http.ServeMux.
• Requests can be matched based on URL host, path, path prefix, schemes, header and query values, HTTP methods or using custom matchers.
• URL hosts, paths and query values 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.

1、example

官方文档给出的例子

package main

import (
    "net/http"
    "log"
    "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
    log.Fatal(http.ListenAndServe(":8000", r))
}

2、创建路由

让我们依托上面的例子，跟着源码来分析一下mux包如何实现路由创建，路由匹配

首先看到mux.go

// NewRouter returns a new router instance.
func NewRouter() *Router {
	return &Router{namedRoutes: make(map[string]*Route), KeepContext: false}
}

我们看到NewRoute()实例化了Router
Router的数据结构如下：
主要由父路由parent，已匹配的路由routes，已命名的路由namedRoutes和三个flagstrictSlash，skipClean，useEncodedPath（相关作用由注释可知）组成

type Router struct {
	// Configurable Handler to be used when no route matches.
	NotFoundHandler http.Handler

	// Configurable Handler to be used when the request method does not match the route.
	MethodNotAllowedHandler http.Handler

	// Parent route, if this is a subrouter.
	parent parentRoute
	// Routes to be matched, in order.
	routes []*Route
	// Routes by name for URL building.
	namedRoutes map[string]*Route
	// See Router.StrictSlash(). This defines the flag for new routes.
	strictSlash bool
	// See Router.SkipClean(). This defines the flag for new routes.
	skipClean bool
	// If true, do not clear the request context after handling the request.
	// This has no effect when go1.7+ is used, since the context is stored
	// on the request itself.
	KeepContext bool
	// see Router.UseEncodedPath(). This defines a flag for all routes.
	useEncodedPath bool
	// Slice of middlewares to be called after a match is found
	middlewares []middleware
}

// StrictSlash defines the trailing slash behavior for new routes. The initial
// value is false.
//
// When true, if the route path is "/path/", accessing "/path" will perform a redirect
// to the former and vice versa. In other words, your application will always
// see the path as specified in the route.
//
// When false, if the route path is "/path", accessing "/path/" will not match
// this route and vice versa.
func (r *Router) StrictSlash(value bool) *Router {
	r.strictSlash = value
	return r
}

// SkipClean defines the path cleaning behaviour for new routes. The initial
// value is false. Users should be careful about which routes are not cleaned
//
// When true, if the route path is "/path//to", it will remain with the double
// slash. This is helpful if you have a route like: /fetch/http://xkcd.com/534/
//
// When false, the path will be cleaned, so /fetch/http://xkcd.com/534/ will
// become /fetch/http/xkcd.com/534
func (r *Router) SkipClean(value bool) *Router {
	r.skipClean = value
	return r
}

// UseEncodedPath tells the router to match the encoded original path
// to the routes.
// For eg. "/path/foo%2Fbar/to" will match the path "/path/{var}/to".
//
// If not called, the router will match the unencoded path to the routes.
// For eg. "/path/foo%2Fbar/to" will match the path "/path/foo/bar/to"
func (r *Router) UseEncodedPath() *Router {
	r.useEncodedPath = true
	return r
}

接下来是HandleFunc()，它使用NewRoute()创建了一个新的路由Route
相比于Router，Route的数据结构主要由handler，matchers和regexp组成
接着调用Path()为Route添加路由规则（route.go）

func (r *Router) HandleFunc(path string, f func(http.ResponseWriter,
	*http.Request)) *Route {
	return r.NewRoute().Path(path).HandlerFunc(f)
}

func (r *Router) NewRoute() *Route {
	route := &Route{parent: r, strictSlash: r.strictSlash, skipClean: r.skipClean, useEncodedPath: r.useEncodedPath}
	r.routes = append(r.routes, route)
	return route
}

type Route struct {
	...
	// Request handler for the route.
	handler http.Handler
	// List of matchers.
	matchers []matcher
	// Manager for the variables from host and path.
	regexp *routeRegexpGroup
	...
}

func (r *Route) Path(tpl string) *Route {
	r.err = r.addRegexpMatcher(tpl, regexpTypePath)
	return r
}

Path()调用了addRegexpMatcher()，根据tpl创建正则表达式并调用newRouteRegexp()（regexp.go）。newRouteRegexp()解析了tql，返回一个routeRegexp，用于匹配主机、路径或查询字符串

// addRegexpMatcher adds a host or path matcher and builder to a route.
func (r *Route) addRegexpMatcher(tpl string, typ regexpType) error {
	if r.err != nil {
		return r.err
	}
	r.regexp = r.getRegexpGroup()
	if typ == regexpTypePath || typ == regexpTypePrefix {
		if len(tpl) > 0 && tpl[0] != '/' {
			return fmt.Errorf("mux: path must start with a slash, got %q", tpl)
		}
		if r.regexp.path != nil {
			tpl = strings.TrimRight(r.regexp.path.template, "/") + tpl
		}
	}
	rr, err := newRouteRegexp(tpl, typ, routeRegexpOptions{
		strictSlash:    r.strictSlash,
		useEncodedPath: r.useEncodedPath,
	})
	if err != nil {
		return err
	}
	for _, q := range r.regexp.queries {
		if err = uniqueVars(rr.varsN, q.varsN); err != nil {
			return err
		}
	}
	if typ == regexpTypeHost {
		if r.regexp.path != nil {
			if err = uniqueVars(rr.varsN, r.regexp.path.varsN); err != nil {
				return err
			}
		}
		r.regexp.host = rr
	} else {
		if r.regexp.host != nil {
			if err = uniqueVars(rr.varsN, r.regexp.host.varsN); err != nil {
				return err
			}
		}
		if typ == regexpTypeQuery {
			r.regexp.queries = append(r.regexp.queries, rr)
		} else {
			r.regexp.path = rr
		}
	}
	r.addMatcher(rr)
	return nil
}

// matcher types try to match a request.
type matcher interface {
	Match(*http.Request, *RouteMatch) bool
}

// addMatcher adds a matcher to the route.
func (r *Route) addMatcher(m matcher) *Route {
	if r.err == nil {
		r.matchers = append(r.matchers, m)
	}
	return r
}

最后是HandlerFunc()，它给特定的路由匹配了请求响应函数YourHandler()

// HandlerFunc sets a handler function for the route.
func (r *Route) HandlerFunc(f func(http.ResponseWriter, *http.Request)) *Route {
	return r.Handler(http.HandlerFunc(f))
}

// Handler sets a handler for the route.
func (r *Route) Handler(handler http.Handler) *Route {
	if r.err == nil {
		r.handler = handler
	}
	return r
}

3、路由匹配

阅读net/http可以知道，实现了Handler接口的数据结构可以定义自己的ServeHTTP()方法，实现对请求的响应

那么让我们来看看mux包的ServeHTTP()方法，它调用了Match()方法来匹配路由，从而实现了对请求的响应

func (r *Router) ServeHTTP(w http.ResponseWriter, req *http.Request) {
	if !r.skipClean {
		path := req.URL.Path
		if r.useEncodedPath {
			path = req.URL.EscapedPath()
		}
		// Clean path to canonical form and redirect.
		if p := cleanPath(path); p != path {

			// Added 3 lines (Philip Schlump) - It was dropping the query string and #whatever from query.
			// This matches with fix in go 1.2 r.c. 4 for same problem.  Go Issue:
			// http://code.google.com/p/go/issues/detail?id=5252
			url := *req.URL
			url.Path = p
			p = url.String()

			w.Header().Set("Location", p)
			w.WriteHeader(http.StatusMovedPermanently)
			return
		}
	}
	var match RouteMatch
	var handler http.Handler
	if r.Match(req, &match) {
		handler = match.Handler
		req = setVars(req, match.Vars)
		req = setCurrentRoute(req, match.Route)
	}

	if handler == nil && match.MatchErr == ErrMethodMismatch {
		handler = methodNotAllowedHandler()
	}

	if handler == nil {
		handler = http.NotFoundHandler()
	}

	if !r.KeepContext {
		defer contextClear(req)
	}

	handler.ServeHTTP(w, req)
}

Match()方法遍历了Router中的所有Route来匹配请求

func (r *Router) Match(req *http.Request, match *RouteMatch) bool {
	for _, route := range r.routes {
		if route.Match(req, match) {
			// Build middleware chain if no error was found
			if match.MatchErr == nil {
				for i := len(r.middlewares) - 1; i >= 0; i-- {
					match.Handler = r.middlewares[i].Middleware(match.Handler)
				}
			}
			return true
		}
	}

	if match.MatchErr == ErrMethodMismatch {
		if r.MethodNotAllowedHandler != nil {
			match.Handler = r.MethodNotAllowedHandler
			return true
		}

		return false
	}

	// Closest match for a router (includes sub-routers)
	if r.NotFoundHandler != nil {
		match.Handler = r.NotFoundHandler
		match.MatchErr = ErrNotFound
		return true
	}

	match.MatchErr = ErrNotFound
	return false
}

以上是对mux包最基本的功能的分析，更多功能请阅读源码