go web framework gin group api 设计

// RouterGroup is used internally to configure router, a RouterGroup is associated with
// a prefix and an array of handlers (middleware).
type RouterGroup struct {
	Handlers HandlersChain #处理函数
	basePath string  #相对路径
	engine   *Engine #存在哪个engine上
	root     bool  #基于基树判断是否为root
}

	router := gin.New()
	users := router.Group("/users")

// New returns a new blank Engine instance without any middleware attached.
// By default the configuration is:
// - RedirectTrailingSlash:  true
// - RedirectFixedPath:      false
// - HandleMethodNotAllowed: false
// - ForwardedByClientIP:    true
// - UseRawPath:             false
// - UnescapePathValues:     true
func New() *Engine {
	debugPrintWARNINGNew()
	engine := &Engine{
		RouterGroup: RouterGroup{
			Handlers: nil,
			basePath: "/",  #默认为“/”
			root:     true,
		},
		FuncMap:                template.FuncMap{},
		RedirectTrailingSlash:  true,
		RedirectFixedPath:      false,
		HandleMethodNotAllowed: false,
		ForwardedByClientIP:    true,
		AppEngine:              defaultAppEngine,
		UseRawPath:             false,
		UnescapePathValues:     true,
		MaxMultipartMemory:     defaultMultipartMemory,
		trees:                  make(methodTrees, 0, 9),
		delims:                 render.Delims{Left: "{{", Right: "}}"},
		secureJsonPrefix:       "while(1);",
	}
	engine.RouterGroup.engine = engine
	engine.pool.New = func() interface{} {
		return engine.allocateContext()
	}
	return engine
}

// Group creates a new router group. You should add all the routes that have common middlewares or the same path prefix.
// For example, all the routes that use a common middleware for authorization could be grouped.
func (group *RouterGroup) Group(relativePath string, handlers ...HandlerFunc) *RouterGroup {
	return &RouterGroup{
		Handlers: group.combineHandlers(handlers),
		basePath: group.calculateAbsolutePath(relativePath), #根据relativePath这个参数，计算basePath
		engine:   group.engine,
	}
}

func (group *RouterGroup) calculateAbsolutePath(relativePath string) string {
	return joinPaths(group.basePath, relativePath)
}

func joinPaths(absolutePath, relativePath string) string {
	if relativePath == "" { #如果没有relativePath 直接返回absolutePath,默认为“/”
		return absolutePath
	}
        #处理最后的“/”
	finalPath := path.Join(absolutePath, relativePath)
	appendSlash := lastChar(relativePath) == ‘/‘ && lastChar(finalPath) != ‘/‘
	if appendSlash {
		return finalPath + "/"
	}
	return finalPath
}