Replace RedirectSlashes with smartRedirectSlashes

[tchssk]

Related to #3366

RedirectSlashes middleware was not suitable for Goa.

RedirectSlashes redirects a request with a trailing slash to the same path without slash.
It also works for patterns with a trailing slash, so they are no longer accesible.
(@ikawaha told me that. Thank you so much.)

I replaced the middleware with a new one.
It redirects both paths with and withohut a trailing slash according to defined patterns.

[ikawaha]

FYI: @tchssk

case 1: mux router

router := httptreemux.New()
router.GET("/about", pageHandler)
router.GET("/posts/", postIndexHandler)
router.POST("/posts", postFormHandler)

case 2: chi router

router := chi.NewRouter()
router.Get("/about", pageHandler)
router.Get("/posts/", postIndexHandler)
router.Post("/posts", postFormHandler)

case 3: chi + RedirectSlashes

router := chi.NewRouter()
router.Use(middleware.RedirectSlashes)
router.Get("/about", pageHandler)
router.Get("/posts/", postIndexHandler)
router.Post("/posts", postFormHandler)

mux	GET:/about	---	GET:/posts/	---	POST:/posts	---
access	GET:/about	GET:/about/	GET:/posts/	GET:/posts	POST:/posts	POST:/posts/
treemux	/about	/about	/posts/	/posts/	/posts/	/posts/
chi	/about	404	/posts/	405	/posts	405
chi+RedirectSlashes	/about	/about	301	301	/posts	/posts

What would be the accessibility of this chi+smrtRedirectSlashes combination?

[tchssk]

If patterns are defined in design as

GET("/about")
GET("/posts/")
POST("/posts")

the routings would be as follows

Request	GET /about	GET /about/	GET /posts/	GET /posts	POST /posts	POST /posts/
httptreemux	/about	301 (/about)	/posts/	301 (/posts/)	301 (/posts/)	/posts/
chi	/about	404	/posts/	405	/posts	405
chi+RedirectSlashes	/about	301 (/about)	301 (/posts)	405	/posts	301 (/posts)
chi+smartRedirectSlashes	/about	301 (/about)	/posts/	301 (/posts/)	/posts	301 (/posts)

POST /posts and POST /posts/ are not compatible between httptreemux and smartRedirectSlashes.

In httphtreemux, if a pattern with a trailing slash is added for a method , all other methods for that pattern will also be considered to have a trailing slash. This is not covered by smartRedirectSlashes because it's about routing and needs to be resolved when registering the handlers.

[ikawaha]

LGTM, if backward compatibility with treemux is important.
It may be an option not to use such a redirection at all, since chi's router does only strict routing.

[raphael]

Great discussion!

In httphtreemux, if a pattern with a trailing slash is added for a method , all other methods for that pattern will also be considered to have a trailing slash.

Maybe we have an opportunity to remove this implicit behavior as we move to chi. We do need to consider backwards compatibility though. Here are my thoughts:

• We add the SmartRedirectSlashes as a public and well documented function in the Goa http package. In particular the header comment could explain that it exists to make the behavior similar to httptreemux and that the middleware should be mounted on the mux.
• We do not mount that middleware by default, that is by default the Goa mux uses strict routing.

This way the new behavior is less surprising but users that rely on the implicit redirect can mount the middleware.

[tchssk]

That makes sense.
I'll move the middleware under http package.

[tchssk]

I created new two pull requests.

• Revert "Use RedirectSlashes middleware by default Goa mux " #3392
• Add SmartRedirectSlashes to http/middleware #3393