go語言原生http庫分析 (2)

這是一個建立於 的文章，其中的資訊可能已經有所發展或是發生改變。

這裡我們分析預設的Handler–DefaultServeMux
在所有介紹之前，我們先給出兩個類：

type ServeMux struct {    mu    sync.RWMutex    m     map[string]muxEntry    hosts bool // whether any patterns contain hostnames}type muxEntry struct {    explicit bool    h        Handler    pattern  string}

ServeMux實現了Handler借口的ServeHTTP函數；我們知道GO語言中，實現了介面的所有函數，則實現該介面

// ServeHTTP dispatches the request to the handler whose// pattern most closely matches the request URL.func (mux *ServeMux) ServeHTTP(w ResponseWriter, r *Request) {    if r.RequestURI == "*" {        if r.ProtoAtLeast(1, 1) {            w.Header().Set("Connection", "close")        }        w.WriteHeader(StatusBadRequest)        return    }    h, _ := mux.Handler(r)    h.ServeHTTP(w, r)}

。接著我們繼續DefaultServeMux，我們在上篇的例子中雖然沒有傳入Handler對象，但是我們有這樣一行代碼：

 http.HandleFunc("/hello", SayHello)  

其實這行代碼操作的就是預設的Handler對象DefaultServeMux，為特定的URL設定處理函數。我們看下該函數，具體做了哪些操作：

func HandleFunc(pattern string, handler func(ResponseWriter, *Request)) {    DefaultServeMux.HandleFunc(pattern, handler)}

簡單粗暴，直接就是調用DefaultServeMux對象的HandleFunc函數，其實DefaultServeMux是一個ServeMux對象：

// NewServeMux allocates and returns a new ServeMux.func NewServeMux() *ServeMux { return &ServeMux{m: make(map[string]muxEntry)} }// DefaultServeMux is the default ServeMux used by Serve.var DefaultServeMux = NewServeMux()

DefaultServeMux對象的HandleFunc函數，也即ServeMux的成員函數：

// HandleFunc registers the handler function for the given pattern.func (mux *ServeMux) HandleFunc(pattern string, handler func(ResponseWriter, *Request)) {    mux.Handle(pattern, HandlerFunc(handler))}

該函數是Handle(pattern, HandlerFunc(handler))的封裝：

// Handle registers the handler for the given pattern.// If a handler already exists for pattern, Handle panics.func (mux *ServeMux) Handle(pattern string, handler Handler) {    mux.mu.Lock()    defer mux.mu.Unlock()    if pattern == "" {        panic("http: invalid pattern " + pattern)    }    if handler == nil {        panic("http: nil handler")    }    if mux.m[pattern].explicit {        panic("http: multiple registrations for " + pattern)    }    mux.m[pattern] = muxEntry{explicit: true, h: handler, pattern: pattern}    if pattern[0] != '/' {        mux.hosts = true    }    // Helpful behavior:    // If pattern is /tree/, insert an implicit permanent redirect for /tree.    // It can be overridden by an explicit registration.    n := len(pattern)    if n > 0 && pattern[n-1] == '/' && !mux.m[pattern[0:n-1]].explicit {        // If pattern contains a host name, strip it and use remaining        // path for redirect.        path := pattern        if pattern[0] != '/' {            // In pattern, at least the last character is a '/', so            // strings.Index can't be -1.            path = pattern[strings.Index(pattern, "/"):]        }        url := &url.URL{Path: path}        mux.m[pattern[0:n-1]] = muxEntry{h: RedirectHandler(url.String(), StatusMovedPermanently), pattern: pattern}    }}

其實簡要之，就是構建一個pattern和函數Handler的map。看來原生庫中實現了路由非常簡單，就是一張map，所以實際應用中局限性比較大。實際應用中，我們往往利用其它路由實現，有必要也可能自己實現。