Add PathStripRegex rule

[seguins]

Fixes #928

[emilevauge]

@seguins thanks for your contribution. I think we should avoid adding a dependency to github.com/containous/mux in middlewares/. Do you think you could add some interface tricks into this?

[seguins]

I think we can create an interface for the matching, and move the github.com/containous/mux part to the main package:

type PrefixMatcher interface {
	Match(r *http.Request) (bool, string)
}

The stripPrefix file cloud be:

package middlewares

import (
	"net/http"
)

type PrefixMatcher interface {
	Match(r *http.Request) (bool, string)
}

// StripPrefix is a middleware used to strip prefix from an URL request
type StripPrefix struct {
	Handler http.Handler
	matcher PrefixMatcher
}

// NewStripPrefix builds a new StripPrefix given a handler and prefixes
func NewStripPrefix(handler http.Handler, matcher PrefixMatcher) *StripPrefix {
	stripPrefix := StripPrefix{Handler: handler, matcher: matcher}
	return &stripPrefix
}

func (s *StripPrefix) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	if match, prefix := s.matcher.Match(r); match == true {
		r.URL.Path = r.URL.Path[len(prefix):]
		r.RequestURI = r.URL.RequestURI()
		s.Handler.ServeHTTP(w, r)
		return
	}
	http.NotFound(w, r)
}

// SetHandler sets handler
func (s *StripPrefix) SetHandler(Handler http.Handler) {
	s.Handler = Handler
}

---

For you information, I have checked other files in middlewares, and I found that handlerSwitcher.go and routes.go already use github.com/containous/mux.

@emilevauge do you think we should do this change ?

[emilevauge]

@seguins
You right, let's keep the dep to github.com/containous/mux.
Would you consider creating a PathStripRegex instead of reusing PathStrip ? I fear that adding regex check in PathStrip will slow down the process for all other requests.

[seguins]

@emilevauge, I've pushed a version with the regex matching separated.

[ldez]

Great job @seguins! Could you fix this https://travis-ci.org/containous/traefik/jobs/226814163#L827 ? Thanks.

[seguins]

Fixed 😃

[ldez]

LGTM

[emilevauge]

Thanks @seguins, awesome job :)
LGTM