net/http: provide an option to access /index.html directly without 301 redirect

[ahuigo]

What version of Go are you using (go version)?

$ go version
go1.18, go1.17, ...(may be all versions)

What did you do?

I found that https://github.com/golang/go/blob/master/src/net/http/fs.go#L590 will redirect /index.html to / with 301 status code.

This 301 action may cause some problems for service worker's cache(https://stackoverflow.com/questions/40476938/service-worker-breaking-301-redirects)

In order to stop 301 redirect, I had to hack official GONIC code

What did you expect to see?

PWA(web app) could cache the start_url:"/index.html" (301 redirect)

What did you see instead?

Since Service Worker breaking 301 redirects, my PWA app can't cache the start_url:"/index.html"

I think it's better to have an option an option to access /index.html directly without 301 redirect. (If possible, I could submit a PR)

[mknyszek]

CC @neild

[seankhliao]

you could just use start_url: "/" ?

[ahuigo]

you could just use start_url: "/" ?

@seankhliao This is not my own PWA app, I think it is unreasonable and unacceptable to modify someone else's code(e.g., https://github.com/mdn/pwa-examples).

Imagine other scenario, I want /index.html to show index pages and / to list file list. It's too hard too implement this with net/http/fs

[neild]

I think it's reasonable to want an http.FileServer that doesn't redirect .../index.html requests, but I'm not sure what the API for it should be.

One thought might be to only redirect an .../index.html request if the index.html file doesn't exist. That is, try opening the file, and only consider redirecting the request if the open fails.

[ahuigo]

I think the easiest way to do this is to provide an optional chained method like this:

	fileServer := http.FileServer(fs)

	////  Is better to let http.FileServer return Struct instead of interface? 
	// fileServer := http.FileServer(fs).SkipPermanentRedirect() 

	// skip 301 redirect
	fileServer.(*http.FileHandler).SkipPermanentRedirect()

8a1fd33#diff-334dd14b9fe9d920086cc14ef1a9f13ac90972a7b289b944d00d4a9be6891a98R23

[seankhliao]

In the spirit of http.StripPrefix, this could just be an http middleware layer (untested):

func StripIndex(h http.Handler) http.Handler {
    return http.HandlerFunc(func(rw http.ResponseWriter, r *http.Request {
        r.URL.Path = strings.TrimSuffix(r.URL.Path, "index.html")
        h.ServeHTTP(rw, r)
    })
}