Writing directly into the response writer does not trigger response before hook functions. about echo

[aldas]

You can not set headers after the response body (at least 1 byte) is sent to the client. This is because headers come before body in HTTP response. If your headers depend on the response body (etag header?) you probably can not avoid buffers in case the body is dynamic.

[aldas]

You could use err = tmpl.Execute(c.Response(), nil) instead of err = tmpl.Execute(c.Response().Writer, nil) as echo.Response implements Writer interface.

With err = tmpl.Execute(c.Response(), nil) beforeFuncs will be called.

---

In regards c.Response().Writer,
This is working as intended. Before functions are called only once (when response has not been "commited"), at the time when the headers are written to the response. With c.Response().Writer, you are accessing original writer that echo.Response is meant to wrap thus forgiving all "magick" that Echo response has.

Here:

echo/response.go

Lines 54 to 65 in 584cb85

	func (r *Response) WriteHeader(code int) {
	if r.Committed {
	r.echo.Logger.Warn("response already committed")
	return
	}
	r.Status = code
	for _, fn := range r.beforeFuncs {
	fn()
	}
	r.Writer.WriteHeader(r.Status)
	r.Committed = true
	}

[aldas]

p.s. create your templates out of handler if they are not changing. That way you avoid overhead of parsing that template on each request

	// avoid parsing template in every request
	tmpl := template.Must(template.New("htmlTemplate").Parse("Hello Bug!"))
	
	e.GET("/bug", func(c echo.Context) error {
		if err := tmpl.Execute(c.Response(), nil); err != nil {
			c.Logger().Error(err)
			return err
		}
		return nil
	})

[SKFrozenCloud]

Thank you.

Is saving it first to bytes.Buffer bad? More saving and copying?

Which method between the "workaround" method and the solution you posted do you think is the "best practice"?

[aldas]

Okay, you second argument to tmpl.Execute is nil. Does this probably means that you are outputting totally static HTML? nothing is there changing? If it is so then you do not need templates at all. Just write your HTML string out and you are good to go.

templates are most useful for cases when your output is dynamic. Although maybe you are using templates for convenience because they have ability to "render" subtemplates/fragments into single output. In that case templates are useful.

[SKFrozenCloud]

The code was a minimal code to reproduce the bug.

But I will render it to a buffer then use the built-in response function.
I had some issues when writing directly to the response writer and then setting the header manually because the header had already been written once.