Responding directly in middleware

[SKFrozenCloud]

I know you are not suppose to respond from a middleware but I want to know why and what can go wrong with that.

For example, the middleware.StaticWithConfig() responds directly in the middleware with this function:

func serveFile(c echo.Context, file http.File, info os.FileInfo) error {
	http.ServeContent(c.Response(), c.Request(), info.Name(), info.ModTime(), file)
	return nil
}

c.File() also in the end uses the built-in http.ServeContent() function.

But all the other functions such as c.HTML or c.String... writes in the response with this function:

func (c *context) Blob(code int, contentType string, b []byte) (err error) {
	c.writeContentType(contentType)
	c.response.WriteHeader(code)
	_, err = c.response.Write(b)
	return
}

My question is: Can I return a response in a middleware with c.Blob()?

[aldas]

You can respond from middleware but make sure to return from current middleware so next(c) will not try to write already "commited" response.

Note:

• commited means that something already send the response (status+headers+body) to the client and because of how HTTP works we can not send headers/status anymore.
• usually when middleware/handler returns error the response has not been committed. So anything up in unwinding call chain can decide to "consume" the error and respond.

Example of one rare place where Commited is checked

echo/echo.go

Line 421 in 60fc2fb

if c.Response().Committed {

I hope this helps

[SKFrozenCloud]

Ok, thank you. So just have to return after responding: return c.Blob().