【Gin-API系列】Gin中间件之异常处理（六）

本文我们介绍生产环境上如何通过捕捉异常recovery来完善程序设计和提高用户体验。

Golang异常处理

golang 的异常处理比较简单，通常都是在程序遇到异常崩溃panic之后通过defer调用延迟函数捕捉异常，并对异常信息进行输出和记录。

• 异常处理代码

defer func() {   
    if err := recover(); err != nil {   
        fmt.Println(err)   
        ... // 上报异常 或者 发送告警
    }   
}()

通过Gin中间件捕捉异常

• 内置中间件
  gin在gin.Default中就使用了自带的Recovery函数，将状态码置为500并输出错误信息到终端

func Recovery() HandlerFunc {
	return RecoveryWithWriter(DefaultErrorWriter)
}

// RecoveryWithWriter returns a middleware for a given writer that recovers from any panics and writes a 500 if there was one.
func RecoveryWithWriter(out io.Writer) HandlerFunc {
	var logger *log.Logger
	if out != nil {
		logger = log.New(out, "\n\n\x1b[31m", log.LstdFlags)
	}
	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()
	}
}

• 自定义中间件
  内置的Recovery函数功能比较简单，我们需要重新开发自定义的异常处理中间件。
  在Gin-IPs项目中我们将堆栈信息上报到Redis，方便监控。同时，我们还通过traceId对该请求进行简单的链路跟踪，可以方便定位到请求日志。

// 日志打印没必要异步处理，一般crash比较少
func Recovery() gin.HandlerFunc {
	log, _ := mylog.New(
		configure.GinConfigValue.ErrorLog.Path, configure.GinConfigValue.ErrorLog.Name,
		configure.GinConfigValue.ErrorLog.Level, nil, configure.GinConfigValue.ErrorLog.Count)
	log.Info("Test Panic")
	return func(c *gin.Context) {
		defer func() {
			if err := recover(); err != nil {
				response := route_response.Response{}
				response.Data.List = []interface{}{} // 初始化为空切片，而不是空引用
				traceId := c.Writer.Header().Get("X-Request-Trace-Id")
				stackMsg := string(debug.Stack())
				logField := map[string]interface{}{
					"trace_id":    traceId, //  鉴权之后可以得到唯一跟踪ID和用户名
					"user":        c.Writer.Header().Get("X-Request-User"),
					"uri":         c.Request.URL.Path,
					"remote_addr": c.ClientIP(),
					"stack":       stackMsg, // 打印堆栈信息
				}
				c.Abort()
				response.Code, response.Message = configure.ApiInnerResponseError, fmt.Sprintf("Api内部报错，请联系管理员(id=%s", traceId)
				log.WithFields(logField).Error(err) // 输出panic 信息
				redisField := make(map[string]interface{})
				for k, v := range logField {
					redisField[k] = v
				}
				redisField["time"] = time.Now().Format("2006-01-02 15:04:05")
				redisField["error"] = err
				dao.ModelClient.RedisClient.HMSet(traceId, redisField) // 上报redis
				c.JSON(http.StatusUnauthorized, response)
				return
			}
		}()

		c.Next()
	}
}

• redis查询异常

10.2.147.167:11700[1]> keys *
1) "445ffc1bb864000"
2) "445ff1b25864000"

10.2.147.167:11700[1]> hgetall 445ffc1bb864000
1) "time"
 2) "2020-09-03 16:42:46"
 3) "error"
 4) "this is test panic"
 5) "user"
 6) "xiaoming"
 7) "remote_addr"
 8) "127.0.0.1"
 9) "uri"
10) "/"
11) "stack"
12) "goroutine 274...."   # ...省略

至此，我们将异常捕捉模块也完成了，这其中不仅涉及到异常处理，还简单的完成了程序内部请求链路跟踪，异常信息落地到Redis也为日后的运维监控做好准备。

Github 代码

请访问 Gin-IPs 或者搜索 Gin-IPs