Redirect request if it would match with an appended trailing slash

pkg/upstream/proxy.go

@@ -1,6 +1,7 @@
 package upstream
 
 import (
+	"context"
 	"fmt"
 	"net/http"
 	"net/url"
@@ -50,6 +51,8 @@ func NewProxy(upstreams options.Upstreams, sigData *options.SignatureData, write
 			return nil, fmt.Errorf("unknown scheme for upstream %q: %q", upstream.ID, u.Scheme)
 		}
 	}
+
+	registerTrailingSlashHandler(m.serveMux)
 	return m, nil
 }
 
@@ -120,3 +123,25 @@ func (m *multiUpstreamProxy) registerRewriteHandler(upstream options.Upstream, h
 
 	return nil
 }
+
+// registerTrailingSlashHandler creates a new matcher that will check if the
+// requested path would match if it had a trailing slash appended.
+// If the path matches with a trailing slash, we send back a redirect.
+// This allows us to be consistent with the built in go servemux implementation.
+func registerTrailingSlashHandler(serveMux *mux.Router) {
+	serveMux.MatcherFunc(func(req *http.Request, _ *mux.RouteMatch) bool {
+		if strings.HasSuffix(req.URL.Path, "/") {
+			return false
+		}
+
+		// Use a separate RouteMatch so that we can redirect to the path + /.
+		// If we pass through the match then the matched backed will be served
+		// instead of the redirect handler.
+		m := &mux.RouteMatch{}
+		slashReq := req.Clone(context.Background())
+		slashReq.URL.Path += "/"
+		return serveMux.Match(slashReq, m)
+	}).Handler(http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {
+		http.Redirect(rw, req, req.URL.String()+"/", http.StatusMovedPermanently)
+	}))
+}

pkg/upstream/proxy_test.go

@@ -29,6 +29,7 @@ var _ = Describe("Proxy Suite", func() {
 		}
 
 		ok := http.StatusOK
+		accepted := http.StatusAccepted
 
 		upstreams := options.Upstreams{
 			{
@@ -47,6 +48,12 @@ var _ = Describe("Proxy Suite", func() {
 				Static:     true,
 				StaticCode: &ok,
 			},
+			{
+				ID:         "static-backend-no-trailing-slash",
+				Path:       "/static",
+				Static:     true,
+				StaticCode: &accepted,
+			},
 			{
 				ID:   "bad-http-backend",
 				Path: "/bad-http/",
@@ -235,5 +242,25 @@ var _ = Describe("Proxy Suite", func() {
 			},
 			upstream: "backend-with-rewrite-prefix",
 		}),
+		Entry("with a request to a path, missing the trailing slash", &proxyTableInput{
+			target: "http://example.localhost/http",
+			response: testHTTPResponse{
+				code: 301,
+				header: map[string][]string{
+					contentType: {textHTMLUTF8},
+					"Location":  {"http://example.localhost/http/"},
+				},
+				raw: "<a href=\"http://example.localhost/http/\">Moved Permanently</a>.\n\n",
+			},
+		}),
+		Entry("with a request to a path, missing the trailing slash, but registered separately", &proxyTableInput{
+			target: "http://example.localhost/static",
+			response: testHTTPResponse{
+				code:   202,
+				header: map[string][]string{},
+				raw:    "Authenticated",
+			},
+			upstream: "static-backend-no-trailing-slash",
+		}),
 	)
 })

pkg/upstream/upstream_suite_test.go

@@ -59,6 +59,7 @@ const (
 	acceptEncoding  = "Accept-Encoding"
 	applicationJSON = "application/json"
 	textPlainUTF8   = "text/plain; charset=utf-8"
+	textHTMLUTF8    = "text/html; charset=utf-8"
 	gapAuth         = "Gap-Auth"
 	gapSignature    = "Gap-Signature"
 )