1. Gin简介
前面通过两篇文章分享了Golang HTTP编程的路由分发、请求/响应处理。
Golang HTTP编程及源码解析-路由分发
Golang HTTP编程及源码解析-请求/响应处理
可以看出来Golang原生HTTP编程在路由分组、动态路由及参数读取/验证、构造String/Data/JSON/HTML响应的方法等存在优化的空间。
Gin是一个用Golang编写的高性能Web框架。
基于前缀树的路由，快速且支持动态路由
支持中间件及路由分组，将具有同一特性的路由划入统一组别、设置相同的中间件。
比如需要登录的一批接口接入登录权限认证中间件、而不需要登录一批接口则不需要接入
...
2. 快速使用
基于gin@v1.8.1，基本使用如下
func main() {
// Creates a new blank Engine instance without any middleware attached
engine := gin.New()
// Global middleware
// Logger middleware will write the logs to gin.DefaultWriter even if you set with GIN_MODE=release.
// By default gin.DefaultWriter = os.Stdout
engine.Use(gin.Logger())
// Recovery middleware recovers from any panics and writes a 500 if there was one.
engine.Use(gin.Recovery())
v1Group := engine.Group("app/v1", accessHandler())
v1Group.GET("user/info", userInfoLogic())
engine.Run(":8019")
}终端运行go run main.go，输出如下
$ go run main.go
[GIN-debug] [WARNING] Running in "debug" mode. Switch to "release" mode in production.
- using env: export GIN_MODE=release
- using code: gin.SetMode(gin.ReleaseMode)
[GIN-debug] GET /app/v1/user/info --> main.userInfoLogic.func1 (4 handlers)
[GIN-debug] [WARNING] You trusted all proxies, this is NOT safe. We recommend you to set a value.
Please check https://pkg.go.dev/github.com/gin-gonic/gin#readme-don-t-trust-all-proxies for details.
[GIN-debug] Listening and serving HTTP on :8019通过打印可以看出注册了GET方法的路由/app/v1/user/info，对应处理函数为main.userInfoLogic，
总共包括四个处理函数，按顺序为gin.Logger()、gin.Recovery() 、accessHandler()以及userInfoLogic
最终在端口8019启动了HTTP监听服务。
2.1 创建Engine并使用gin.Logger()和 gin.Recovery() 两个全局中间件，对engine下的所有路由都生效
通过代码及注释，gin.Logger()和 gin.Recovery()放到了Engine.RouterGroup.Handlers切片中。
// Use attaches a global middleware to the router. i.e. the middleware attached through Use() will be
// included in the handlers chain for every single request. Even 404, 405, static files...
// For example, this is the right place for a logger or error management middleware.
func (engine *Engine) Use(middleware ...HandlerFunc) IRoutes {
engine.RouterGroup.Use(middleware...)
engine.rebuild404Handlers()
engine.rebuild405Handlers()
return engine
}
// Use adds middleware to the group, see example code in GitHub.
func (group *RouterGroup) Use(middleware ...HandlerFunc) IRoutes {
group.Handlers = append(group.Handlers, middleware...)
return group.returnObj()
}2.2 创建路由分组v1Group，且该分组使用了accessHandler()，accessHandler()对v1Group分组路由均生效
// 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),
engine: group.engine,
}
}从代码可以看出，返回了新的gin.RouterGroup，并且
v1Group.Handlers = append(group.Handlers, handlers)，此时gin.RouterGroup.Handlers为[gin.Logger(),gin.Recovery(),accessHandler()]
同时v1Group.basePath = "app/v1"
从代码同时可以得出，支持分组嵌套分组。即在v1Group都基础上在创建分组，比如v1Group.Group("north")
2.3 在v1Group下注册路由user/info，该路由的处理函数是userInfoLogic，方法为GET
func (group *RouterGroup) handle(httpMethod, relativePath string, handlers HandlersChain) IRoutes {
absolutePath := group.calculateAbsolutePath(relativePath) // 计算出完整路由
handlers = group.combineHandlers(handlers) // 将新处理函数拼接到原来的末尾
group.engine.addRoute(httpMethod, absolutePath, handlers) // 路由加入到前缀树
return group.returnObj()
}
func (engine *Engine) addRoute(method, path string, handlers HandlersChain) {
...
root := engine.trees.get(method)
if root == nil {
root = new(node)
root.fullPath = "/"
engine.trees = append(engine.trees, methodTree{method: method, root: root})
}
root.addRoute(path, handlers)
...
}将分组v1Group的路由前缀和当前user/info计算得到完整路由，即app/v1/user/info
合并处理函数，此时handlers = [gin.Logger(),gin.Recovery(),accessHandler(),userInfoLogic()]
最后将路由及处理函数按http method分组，加入到不同路由树中。
2.4 通过 engine.Run(":8019") 在启动HTTP服务
// Run attaches the router to a http.Server and starts listening and serving HTTP requests.
// It is a shortcut for http.ListenAndServe(addr, router)
// Note: this method will block the calling goroutine indefinitely unless an error happens.
func (engine *Engine) Run(addr ...string) (err error) {
...
address := resolveAddress(addr)
debugPrint("Listening and serving HTTP on %s\n", address)
err = http.ListenAndServe(address, engine.Handler())
return
}这里调用http.ListenAndServe启动HTTP监听服务，Engine实现了http.Handler接口，如果有客户端请求，会调用到Engine.ServeHTTP函数。
3. 路由过程
// gin.go
func (engine *Engine) handleHTTPRequest(c *Context) {
httpMethod := c.Request.Method
rPath := c.Request.URL.Path
...
// Find root of the tree for the given HTTP method
t := engine.trees
for i, tl := 0, len(t); i < tl; i++ {
if t[i].method != httpMethod {
continue
}
root := t[i].root
// Find route in tree
value := root.getValue(rPath, c.params, c.skippedNodes, unescape)
if value.params != nil {
c.Params = *value.params
}
if value.handlers != nil {
c.handlers = value.handlers
c.fullPath = value.fullPath
c.Next()
c.writermem.WriteHeaderNow()
return
}
...
break
}
}
// context.go
func (c *Context) Next() {
c.index++
for c.index < int8(len(c.handlers)) {
c.handlers[c.index](c)
c.index++
}
}从上面代码可以看出，通过http method找到对应的路由树，再根据URL从路由树中查找对应的节点，
获取到处理函数切片，通过c.Next按通过顺序执行处理函数。
对于请求GET /app/v1/user/info，将依次执行[gin.Logger(),gin.Recovery(),accessHandler(),userInfoLogic()]
4. 请求/响应参数处理
func accessHandler() func(*gin.Context) {
return func(c *gin.Context) {
// 不允许crul访问
if strings.Contains(c.GetHeader("user-agent"), "curl") {
c.JSON(http.StatusBadRequest, "cant't not visited by curl")
c.Abort() // 直接退出，避免执行后续处理函数
}
}
}
func userInfoLogic() func(*gin.Context) {
return func(c *gin.Context) {
id := c.Query("id")
c.JSON(http.StatusOK, map[string]interface{}{"id": id, "name": "bob", "age": 18})
}
}v1Group的通用处理函数accessHandler，达到v1Group下注册的路由无法用curl访问的效果。
通过c.Query("id") 获取URL查询参数，
通过以下代码可以看出，第一次获取URL查询时会缓存所有URL查询参数，这减少了内存的分配，节省了计算资源。
因为每次调用url.ParseQuery都会重新申请缓存，重复解析URL。
func (c *Context) Query(key string) (value string) {
value, _ = c.GetQuery(key)
return
}
func (c *Context) initQueryCache() {
if c.queryCache == nil {
if c.Request != nil {
c.queryCache = c.Request.URL.Query()
} else {
c.queryCache = url.Values{}
}
}
}
func (c *Context) GetQueryArray(key string) (values []string, ok bool) {
c.initQueryCache()
values, ok = c.queryCache[key]
return
}通过c.JSON返回Content-Type为application/json的响应体，
这也是Gin对原生net/http编程的一个优化，对常用的响应类型进行封装，方便使用者使用。
当然，Gin对请求/响应参数的处理还有其它很多细微的优化，这里就不详细说明了。
5. 总结
Gin使用Map来实现路由匹配，而Gin使用路由树来实现路由匹配，支持动态路由，内存占用小且路由匹配快。
同时Gin使用缓存来优化请求参数的处理过程，提供了通用的响应参数处理等，方便用户使用。
