gin架構源碼學習筆記(二)中間件

gin 預設時使用了logger和recovery兩個中間件。

// Default returns an Engine instance with the Logger and Recovery middleware already attached.
func Default() *Engine {
	debugPrintWARNINGDefault()
	engine := New()
	engine.Use(Logger(), Recovery())
	return engine
}
           

Use()接口會将Logger和Recover()的處理函數追加到Handlers的後面

// Logger instances a Logger middleware that will write the logs to gin.DefaultWriter.
// By default gin.DefaultWriter = os.Stdout.
func Logger() HandlerFunc {
	return LoggerWithConfig(LoggerConfig{})
}
           

// 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()
}
           

這樣每個方法便有了一條handers鍊 :

假設這是一個Get方法

現在看看日志的處理函數做些什麼

// LoggerWithConfig instance a Logger middleware with config.

	return func(c *Context) {
		// Start timer
		start := time.Now()
		path := c.Request.URL.Path
		raw := c.Request.URL.RawQuery

		// Process request
		c.Next()

		// Log only when path is not being skipped
		if _, ok := skip[path]; !ok {
			param := LogFormatterParams{
				Request: c.Request,
				isTerm:  isTerm,
				Keys:    c.Keys,
			}

			// Stop timer
			param.TimeStamp = time.Now()
			param.Latency = param.TimeStamp.Sub(start)

			param.ClientIP = c.ClientIP()
			param.Method = c.Request.Method
			param.StatusCode = c.Writer.Status()
			param.ErrorMessage = c.Errors.ByType(ErrorTypePrivate).String()

			param.BodySize = c.Writer.Size()

			if raw != "" {
				path = path + "?" + raw
			}

			param.Path = path

			fmt.Fprint(out, formatter(param))
		}
	}
           

可以看到 先是記錄了一個開始時間，然後處理

c.Next()

處理完c.Next() 記錄結束時間然後 計算 該條請求消耗的時間，及一些其他客戶資訊列印到終端 . 那說明c.Next() 會處理我們注冊的處理函數， 看看c.Next()

// Next should be used only inside middleware.
// It executes the pending handlers in the chain inside the calling handler.
// See example in GitHub.
func (c *Context) Next() {
	c.index++
	for c.index < int8(len(c.handlers)) {
		c.handlers[c.index](c)
		c.index++
	}
}
           

c.Next()會調用handlers中的其他handler， 我們知道他的下一條handler 是 Recover 的，再看看Recover的handler

return func(c *Context) {
		defer func() {
			if err := recover(); err != nil {
				// Check for a broken connection, as it is not really a
				// condition that warrants a panic stack trace.
				var brokenPipe bool
				if ne, ok := err.(*net.OpError); ok {
					if se, ok := ne.Err.(*os.SyscallError); ok {
						if strings.Contains(strings.ToLower(se.Error()), "broken pipe") || strings.Contains(strings.ToLower(se.Error()), "connection reset by peer") {
							brokenPipe = true
						}
					}
				}
				if logger != nil {
					stack := stack(3)
					httpRequest, _ := httputil.DumpRequest(c.Request, false)
					headers := strings.Split(string(httpRequest), "\r\n")
					for idx, header := range headers {
						current := strings.Split(header, ":")
						if current[0] == "Authorization" {
							headers[idx] = current[0] + ": *"
						}
					}
					if brokenPipe {
						logger.Printf("%s\n%s%s", err, string(httpRequest), reset)
					} else if IsDebugging() {
						logger.Printf("[Recovery] %s panic recovered:\n%s\n%s\n%s%s",
							timeFormat(time.Now()), strings.Join(headers, "\r\n"), err, stack, reset)
					} else {
						logger.Printf("[Recovery] %s panic recovered:\n%s\n%s%s",
							timeFormat(time.Now()), err, stack, reset)
					}
				}

				// If the connection is dead, we can't write a status to it.
				if brokenPipe {
					c.Error(err.(error)) // nolint: errcheck
					c.Abort()
				} else {
					c.AbortWithStatus(http.StatusInternalServerError)
				}
			}
		}()
		c.Next()
	}
           

可以看到有個defer, recover()應該先通過c.Next()處理了使用者的的handler() 如果使用者handler()崩潰了，就進行恢複，不會因為一個請求導緻伺服器挂掉以影響其他請求的處理。

也就是說它最後的調用的順序會是這樣的，

gin架構還是很靈活的，這樣我們也能定制自己的中間件進行擴充了。