Added ReplacePathRegex middleware

docs/basics.md

@@ -86,6 +86,7 @@ Following is the list of existing modifier rules:
 
 - `AddPrefix: /products`: Add path prefix to the existing request path prior to forwarding the request to the backend.
 - `ReplacePath: /serverless-path`: Replaces the path and adds the old path to the `X-Replaced-Path` header. Useful for mapping to AWS Lambda or Google Cloud Functions.
+- `ReplacePathRegex: ^/api/v2/(.*) /api/$1`: Replaces the path with a regular expression and adds the old path to the `X-Replaced-Path` header. Separate the regular expression and the replacement by a space.
 
 #### Matchers
 

middlewares/replace_path_regex.go

@@ -0,0 +1,38 @@
+package middlewares
+
+import (
+	"net/http"
+	"regexp"
+	"strings"
+
+	"github.com/containous/traefik/log"
+)
+
+// ReplacePathRegex is a middleware used to replace the path of a URL request with a regular expression
+type ReplacePathRegex struct {
+	Handler     http.Handler
+	Regexp      *regexp.Regexp
+	Replacement string
+}
+
+// NewReplacePathRegexHandler returns a new ReplacePathRegex
+func NewReplacePathRegexHandler(regex string, replacement string, handler http.Handler) http.Handler {
+	exp, err := regexp.Compile(strings.TrimSpace(regex))
+	if err != nil {
+		log.Errorf("Error compiling regular expression %s: %s", regex, err)
+	}
+	return &ReplacePathRegex{
+		Regexp:      exp,
+		Replacement: strings.TrimSpace(replacement),
+		Handler:     handler,
+	}
+}
+
+func (s *ReplacePathRegex) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	if s.Regexp != nil && len(s.Replacement) > 0 && s.Regexp.MatchString(r.URL.Path) {
+		r.Header.Add(ReplacedPathHeader, r.URL.Path)
+		r.URL.Path = s.Regexp.ReplaceAllString(r.URL.Path, s.Replacement)
+		r.RequestURI = r.URL.RequestURI()
+	}
+	s.Handler.ServeHTTP(w, r)
+}

middlewares/replace_path_regex_test.go

@@ -0,0 +1,80 @@
+package middlewares
+
+import (
+	"net/http"
+	"testing"
+
+	"github.com/containous/traefik/testhelpers"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestReplacePathRegex(t *testing.T) {
+	testCases := []struct {
+		desc           string
+		path           string
+		replacement    string
+		regex          string
+		expectedPath   string
+		expectedHeader string
+	}{
+		{
+			desc:           "simple regex",
+			path:           "/whoami/and/whoami",
+			replacement:    "/who-am-i/$1",
+			regex:          `^/whoami/(.*)`,
+			expectedPath:   "/who-am-i/and/whoami",
+			expectedHeader: "/whoami/and/whoami",
+		},
+		{
+			desc:           "simple replace (no regex)",
+			path:           "/whoami/and/whoami",
+			replacement:    "/who-am-i",
+			regex:          `/whoami`,
+			expectedPath:   "/who-am-i/and/who-am-i",
+			expectedHeader: "/whoami/and/whoami",
+		},
+		{
+			desc:           "multiple replacement",
+			path:           "/downloads/src/source.go",
+			replacement:    "/downloads/$1-$2",
+			regex:          `^(?i)/downloads/([^/]+)/([^/]+)$`,
+			expectedPath:   "/downloads/src-source.go",
+			expectedHeader: "/downloads/src/source.go",
+		},
+		{
+			desc:         "invalid regular expression",
+			path:         "/invalid/regexp/test",
+			replacement:  "/valid/regexp/$1",
+			regex:        `^(?err)/invalid/regexp/([^/]+)$`,
+			expectedPath: "/invalid/regexp/test",
+		},
+	}
+
+	for _, test := range testCases {
+		test := test
+		t.Run(test.desc, func(t *testing.T) {
+			t.Parallel()
+
+			var actualPath, actualHeader, requestURI string
+			handler := NewReplacePathRegexHandler(
+				test.regex,
+				test.replacement,
+				http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+					actualPath = r.URL.Path
+					actualHeader = r.Header.Get(ReplacedPathHeader)
+					requestURI = r.RequestURI
+				}),
+			)
+
+			req := testhelpers.MustNewRequest(http.MethodGet, "http://localhost"+test.path, nil)
+
+			handler.ServeHTTP(nil, req)
+
+			assert.Equal(t, test.expectedPath, actualPath, "Unexpected path.")
+			assert.Equal(t, test.expectedHeader, actualHeader, "Unexpected '%s' header.", ReplacedPathHeader)
+			if test.expectedHeader != "" {
+				assert.Equal(t, actualPath, requestURI, "Unexpected request URI.")
+			}
+		})
+	}
+}

server/rules.go

@@ -92,6 +92,13 @@ func (r *Rules) replacePath(paths ...string) *mux.Route {
 	return r.route.route
 }
 
+func (r *Rules) replacePathRegex(paths ...string) *mux.Route {
+	for _, path := range paths {
+		r.route.replacePathRegex = path
+	}
+	return r.route.route
+}
+
 func (r *Rules) addPrefix(paths ...string) *mux.Route {
 	for _, path := range paths {
 		r.route.addPrefix = path
@@ -155,6 +162,7 @@ func (r *Rules) parseRules(expression string, onRule func(functionName string, f
 		"HeadersRegexp":        r.headersRegexp,
 		"AddPrefix":            r.addPrefix,
 		"ReplacePath":          r.replacePath,
+		"ReplacePathRegex":     r.replacePathRegex,
 		"Query":                r.query,
 	}
 

server/server.go

@@ -16,6 +16,7 @@ import (
 	"reflect"
 	"regexp"
 	"sort"
+	"strings"
 	"sync"
 	"time"
 
@@ -81,6 +82,7 @@ type serverRoute struct {
 	stripPrefixesRegex []string
 	addPrefix          string
 	replacePath        string
+	replacePathRegex   string
 }
 
 // NewServer returns an initialized Server.
@@ -1065,6 +1067,15 @@ func (server *Server) wireFrontendBackend(serverRoute *serverRoute, handler http
 		}
 	}
 
+	if len(serverRoute.replacePathRegex) > 0 {
+		sp := strings.Split(serverRoute.replacePathRegex, " ")
+		if len(sp) == 2 {
+			handler = middlewares.NewReplacePathRegexHandler(sp[0], sp[1], handler)
+		} else {
+			log.Warnf("Invalid syntax for ReplacePathRegex: %s. Separate the regular expression and the replacement by a space.", serverRoute.replacePathRegex)
+		}
+	}
+
 	// add prefix - This needs to always be right before ReplacePath on the chain (second in order in this function)
 	// -- Adding Path Prefix should happen after all *Strip Matcher+Modifiers ran, but before Replace (in case it's configured)
 	if len(serverRoute.addPrefix) > 0 {