Add Path Replacement Rule

docs/basics.md

@@ -84,6 +84,7 @@ Modifier rules only modify the request. They do not have any impact on routing d
 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.
 
 ### Matchers
 

middlewares/replace_path.go

@@ -0,0 +1,20 @@
+package middlewares
+
+import (
+	"net/http"
+)
+
+// ReplacePath is a middleware used to replace the path of a URL request
+type ReplacePath struct {
+	Handler http.Handler
+	Path    string
+}
+
+// ReplacedPathHeader is the default header to set the old path to
+const ReplacedPathHeader = "X-Replaced-Path"
+
+func (s *ReplacePath) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	r.Header.Add(ReplacedPathHeader, r.URL.Path)
+	r.URL.Path = s.Path
+	s.Handler.ServeHTTP(w, r)
+}

middlewares/replace_path_test.go

@@ -0,0 +1,44 @@
+package middlewares_test
+
+import (
+	"net/http"
+	"testing"
+
+	"github.com/containous/traefik/middlewares"
+)
+
+func TestReplacePath(t *testing.T) {
+	const replacementPath = "/replacement-path"
+
+	paths := []string{
+		"/example",
+		"/some/really/long/path",
+	}
+
+	for _, path := range paths {
+		t.Run(path, func(t *testing.T) {
+			var newPath, oldPath string
+			handler := &middlewares.ReplacePath{
+				Path: replacementPath,
+				Handler: http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+					newPath = r.URL.Path
+					oldPath = r.Header.Get("X-Replaced-Path")
+				}),
+			}
+
+			req, err := http.NewRequest("GET", "http://localhost"+path, nil)
+			if err != nil {
+				t.Error(err)
+			}
+
+			handler.ServeHTTP(nil, req)
+			if newPath != replacementPath {
+				t.Fatalf("new path should be '%s'", replacementPath)
+			}
+
+			if oldPath != path {
+				t.Fatalf("old path should be '%s'", path)
+			}
+		})
+	}
+}

server/rules.go

@@ -75,6 +75,13 @@ func (r *Rules) pathStrip(paths ...string) *mux.Route {
 	return r.route.route
 }
 
+func (r *Rules) replacePath(paths ...string) *mux.Route {
+	for _, path := range paths {
+		r.route.replacePath = path
+	}
+	return r.route.route
+}
+
 func (r *Rules) addPrefix(paths ...string) *mux.Route {
 	for _, path := range paths {
 		r.route.addPrefix = path
@@ -116,6 +123,7 @@ func (r *Rules) parseRules(expression string, onRule func(functionName string, f
 		"Headers":         r.headers,
 		"HeadersRegexp":   r.headersRegexp,
 		"AddPrefix":       r.addPrefix,
+		"ReplacePath":     r.replacePath,
 	}
 
 	if len(expression) == 0 {

server/server.go

@@ -65,6 +65,7 @@ type serverRoute struct {
 	route         *mux.Route
 	stripPrefixes []string
 	addPrefix     string
+	replacePath   string
 }
 
 // NewServer returns an initialized Server.
@@ -806,6 +807,14 @@ func (server *Server) wireFrontendBackend(serverRoute *serverRoute, handler http
 		}
 	}
 
+	// path replace
+	if len(serverRoute.replacePath) > 0 {
+		handler = &middlewares.ReplacePath{
+			Path:    serverRoute.replacePath,
+			Handler: handler,
+		}
+	}
+
 	serverRoute.route.Handler(handler)
 }