How to Add/Set Header after next() in Golang Echo Middleware?-CodePudding

Main Purpose: I want to simply count the execution time for any API / route, and add it into the Response Header with key: ExecutionTime.

I am very open to another alternative, since my method may wrong as I am still new in Go-Echo framework.

What I have been doing: So this is my middleware code:

func (s *Stats) ExecTime(next echo.HandlerFunc) echo.HandlerFunc {
    return func(c echo.Context) error {
        c.Response().Header().Set("ExecutionStartedAt", time.Now().String())
        if err := next(c); err != nil { //exec main process
            c.Error(err)
        }
        c.Response().Header().Set("ExecutionDoneAt", time.Now().String())
        return nil
    }
}

Current Result:

< HTTP/1.1 200 OK
< Content-Type: application/json; charset=UTF-8
< Executionstartedat: 2022-09-11 16:32:15.612045  0700 WIB m= 3.619364986
< Server: Echo/3.0
< Date: Sun, 11 Sep 2022 09:32:21 GMT
< Content-Length: 856

Please note: There is an Executionstartedat added. But unfortunatelly there is no ExecutionDoneAt as expected.

Expected Result:

< HTTP/1.1 200 OK
< Content-Type: application/json; charset=UTF-8
< Executionstartedat: 2022-09-11 16:32:15.612045  0700 WIB m= 3.619364986
< Executiondoneat: 2022-09-11 16:32:18.612045  0700 WIB m= 3.619364986
< Server: Echo/3.0
< Date: Sun, 11 Sep 2022 09:32:21 GMT
< Content-Length: 856

I am following this documentation: https://echo.labstack.com/cookbook/middleware/#response

Any help, any idea, any alternative ways to accomplish same result would be very very appreciated. Thank you very much.

Edited #1:

What else I have tried:

I have tried to use another middleware, the timing is good, just as I expected. But unfortunately the header is still empty.

    e.Use(middleware.BodyDump(func(c echo.Context, reqBody, resBody []byte) {
        fmt.Println("this is from BodyDump 7: ", time.Now())
        c.Response().Header().Set("ExecutionTime7", "Exec Time: "   time.Now().String())
    }))

The result is exactly like above, no change at all.

Edited #2

here is the working code example:

// ExecTime is the middleware function.
func (s *Stats) ExecTime(next echo.HandlerFunc) echo.HandlerFunc {
    return func(c echo.Context) error {
        before := time.Now()
        c.Response().Header().Set("ExecutionStartedAt", before.String())

        c.Response().Before(func() {
            after := time.Now()
            elapsed := time.Since(before)

            c.Response().Header().Set("ExecutionDoneAt", after.String())
            c.Response().Header().Set("ExecutionTime", elapsed.String())
        })

        if err := next(c); err != nil { //exec main process
            c.Error(err)
        }
        return nil
    }
}

CodePudding user response：

In HTTP the headers go before the body, as the name "header" implies. So once you write the body you cannot write the header. You may try using HTTP/2 Trailers. Or execute the process, but before writing its output to the body, calculate the execution time, add the header, and then write the body.

I don't use echo so I don't know what the correct approach is, but it seems to me like it'd be better if you use the response before hook.

Example by @JackySupit:

// ExecTime is the middleware function.
func (s *Stats) ExecTime(next echo.HandlerFunc) echo.HandlerFunc {
    return func(c echo.Context) error {
        before := time.Now()
        c.Response().Header().Set("ExecutionStartedAt", before.String())

        c.Response().Before(func() {
            after := time.Now()
            elapsed := time.Since(before)

            c.Response().Header().Set("ExecutionDoneAt", after.String())
            c.Response().Header().Set("ExecutionTime", elapsed.String())
        })

        if err := next(c); err != nil { //exec main process
            c.Error(err)
        }
        return nil
    }
}