Strange behavior with groups + mw

[alehano]

I have several groups and some groups use specific middlewares.
But I noticed that in some combination of mw some groups start using middlewares from another groups.

For example:

files:

/static/test.txt
main.go

code:

package main

import (
    "log"

    "github.com/labstack/echo"
    mw "github.com/labstack/echo/middleware"
)

func main() {

    e := echo.New()
    e.Use(mw.Logger())
    e.Use(mw.Recover())
    e.Use(mw.Gzip())

    static := e.Group("/static")
    static.Use(MaxAgeMonth)
    static.ServeDir("/", "static")

    e.Get("/", func(c *echo.Context) error {
        return c.String(200, "Index")
    })

    admStatic := e.Group("/admin/static")
    admStatic.Use(MaxAgeMonth)
    admStatic.ServeDir("/", "admin/static")

    a := e.Group("/admin")
    a.Use(func(c *echo.Context) error {
        log.Println("Admin")
        return nil
    })
    a.Get("/info", func(c *echo.Context) error {
        return c.String(200, "OK")
    })

    e.Run(":8085")

}

func MaxAgeMonth(c *echo.Context) error {
    c.Response().Header().Add("Cache-Control", "max-age=2592000, public")
    return nil
}

So, if you open http://127.0.0.1:8085/static/test.txt
You'll see "Admin" in console. It means that /static/test.txt use another middleware which is in "/admin" group.

But if I remove e.Use(mw.Recover()) or e.Use(mw.Gzip()) everything works ok.
It's really odd.

[vishr]

@alehano I don't see this behavior after I fixed #95, can you confirm?

[alehano]

Yes, it's still there.

2015/06/09 20:22:24 Admin
2015/06/09 20:22:24 GET /static/test.txt 304 775.864µs 0
2015/06/09 20:22:25 Admin
2015/06/09 20:22:25 GET /static/test.txt 304 70.584µs 0
2015/06/09 20:22:27 Admin
2015/06/09 20:22:27 GET /static/test.txt 304 62.229µs 0

[hasty]

This is because Group is relying on unreliable behavior in append. When a new group is created, it makes a copy of the parent echo; this is a shallow copy, though, so g.echo.middleware still points to the parent middleware. That's fine if you don't add any new middleware.

If you do, though, then it's dependent on whether or not the slice has capacity for the new middleware. If it doesn't, then append grows the slice and returns a new pointer to the larger slice, which contains all the parent middleware and the new middleware; this is fine. If you're unlucky and there's enough capacity, it just adds the new middleware to the slice, affecting both the parent echo and any other groups that are pointing at it.

A cheap fix is to just copy over the parent middleware into a new slice the first time you call Use() on Group. This got it working again for me. However, there are other ways that yield different results; for example, Group might keep its own mw list without copying, but then always iterate over the parent middleware before its own (or vice versa, as the case may be). This would allow you to add middleware to the parent echo after creating the group, which may be more like expected behavior.