go http包 DefaultServeMux 有关匹配规则的几个函数

func (mux *ServeMux) match(path string) Handler {
	var h Handler
	var n = 0
	for k, v := range mux.m {
		if !pathMatch(k, path) {
			continue
		}
		if h == nil || len(k) > n {
			n = len(k)
			h = v.h
		}
	}
	return h
}

func pathMatch(pattern, path string) bool {
	if len(pattern) == 0 {
		// should not happen
		return false
	}
	n := len(pattern)
	if pattern[n-1] != '/' {
		return pattern == path
	}
	return len(path) >= n && path[0:n] == pattern
}

func (mux *ServeMux) handler(r *Request) Handler {
	mux.mu.RLock()
	defer mux.mu.RUnlock()

	// Host-specific pattern takes precedence over generic ones
	h := mux.match(r.Host + r.URL.Path)
	if h == nil {
		h = mux.match(r.URL.Path)
	}
	if h == nil {
		h = NotFoundHandler()
	}
	return h
}

总是会请求一个 "/favicon.ico" 所以总是会出现 "/" 被请求了两次