Does middleware always run before endpoint handler?

[winston0410]

Reading the documentation, I notice that it didn't mention whether the middleware would only run before handler, or it can be config to run after a handler. Is it correct to say that at v4, middleware would only be triggered before a handler(this is what I found out by logging). Is it possible to run a middleware after a handler, so I can transform the response body(for example, minify the response)

[aldas]

You can add your logic "after" part inside middleware. See this example:

package main

import (
	"errors"
	"github.com/labstack/echo/v4"
	"log/slog"
	"net/http"
	"os"
)

func main() {
	e := echo.New()

	logger := slog.New(slog.NewJSONHandler(os.Stdout, nil))

	e.Use(func(next echo.HandlerFunc) echo.HandlerFunc {
		return func(c echo.Context) error {
			logger.Info("before calling next middleware/handler")
			err := next(c)
			logger.Info("after calling next middleware/handler")
			return err
		}
	})

	e.GET("/", func(c echo.Context) error {
		logger.Info("inside the handler")
		return c.String(http.StatusOK, "OK")
	})

	if err := e.Start(":8080"); err != nil && !errors.Is(err, http.ErrServerClosed) {
		slog.Error("server closed due to unexpected error", "err", err)
	}
}

[aldas]

you might want to check these middlewares how similar things are done

1. https://github.com/labstack/echo/blob/master/middleware/body_dump.go
2. https://github.com/labstack/echo/blob/master/middleware/compress.go

[winston0410]

That is awesome, thank you for your answer