Log request id in golang logs

I am working on an existing application which is written in Go using framework such as gin, middleware. This application uses https://pkg.go.dev/log for logging.

I am trying to add a request id to the log for the API call trace.

main.go

		// Creates a router without any middleware by default
		r := gin.New()
		r.Use(middleware.RequestID())

middleware.go

func (m *Middleware) CheckApiToken(allowWithoutAccessKey bool, validateTonce ...bool) gin.HandlerFunc {
	return func(c *gin.Context) {

            // Validate
            .....
            .....
			logger.InitializeContext(c)
			c.Next()
		}
	}
}


//RequestID is a middleware that injects a 'RequestID' into the context and header of each request.
func (m *Middleware) RequestID() gin.HandlerFunc {
	return func(c *gin.Context) {
		xRequestID := uuid.NewV4().String()
		c.Request.Header.Set(logger.XRequestIDKey, xRequestID)
		fmt.Printf("[GIN-debug] %s [%s] - \"%s %s\"\n", time.Now().Format(time.RFC3339), xRequestID, c.Request.Method, c.Request.URL.Path)
		c.Next()
	}
}

logger.go

const (
	XRequestIDKey = "X-Request-ID"
)

var (
	infoLogger  *log.Logger
	errorLogger *log.Logger
	context     *gin.Context
)

func init() {

	infoLogger = log.New(os.Stdout, "", 0)
	errorLogger = log.New(os.Stderr, "", 0)
}

// InitializeContext initialize golbal gin context to logger
func InitializeContext(c *gin.Context) {
	context = c
}

//Check if the request id present in the context.
func getRequestID() interface{} {
	if context != nil {
		if context.Request != nil {
			requestID := context.Request.Header.Get(XRequestIDKey)
			if requestID != "" {
				return requestID
			}
		}
	}
	return ""
}

func Info(entry Input) {
	infoLogger.Println(getJSON(getRequestID(), msg))
}

This does not work in multi-threaded environment. How do I fix this solution to fix this in multi-threaded environment.

You cannot save the context in a global variable. Context is by definition local to that execution, and at any given moment, there will be multiple of them.

You can store the generated ID in the gin context:

func (m *Middleware) RequestID() gin.HandlerFunc {
    return func(c *gin.Context) {
        xRequestID := uuid.NewV4().String()
        c.Set("requestId",xRequestID)
        fmt.Printf("[GIN-debug] %s [%s] - \"%s %s\"\n", time.Now().Format(time.RFC3339), xRequestID, c.Request.Method, c.Request.URL.Path)
        c.Next()
    }
}

Then you can use the ID stored in the context with the custom log formatter:

router.Use(gin.LoggerWithFormatter(func(param gin.LogFormatterParams) string {

		return fmt.Sprintf("%s ...",
				param.Keys["requestId"],
               ...
		)
	}))

Or if you need to use a different logging library, you can write a wrapper:

func LogInfo(ctx *gin.Context,msg string) {
   id:=ctx.Get("requestId")
   // Log msg with ID
}

Many log libraries offer methods to get a logger with some parameters already set. For instance, if you use zerolog:

logger:=log.Info().With().Str("requestId",ctx.Get("requestId")).Logger()

logger.Info().Msg("This log msg will contain the request id")