gateway: routable static base path (#3010)

api/config/gateway/v1/gateway.proto

@@ -133,6 +133,11 @@ message Assets {
   oneof provider {
     S3Provider s3 = 1;
   }
+
+  // Clutch hosts static assets on the `/static/` path, any request to this path will result in a lookup of static
+  // assets. However if you would like to utilize this route for other pruposes in additon to static assets, you can
+  // enable this feature. eg: clutch.sh/static || /static/* -> you can now handle this route as you wish.
+  bool routable_static_path = 2;
 }
 
 message Logger {

backend/clutch-config.yaml

@@ -2,6 +2,8 @@ gateway:
   logger:
     pretty: true
     level: DEBUG
+  assets:
+    routableStaticPath: true
   accesslog:
     # log http 5xx errors by default
     status_code_filters:

backend/gateway/mux/mux.go

@@ -30,12 +30,16 @@ import (
 )
 
 const (
-	xHeader        = "X-"
-	xForwardedFor  = "X-Forwarded-For"
-	xForwardedHost = "X-Forwarded-Host"
+	xHeader         = "X-"
+	xForwardedFor   = "X-Forwarded-For"
+	xForwardedHost  = "X-Forwarded-Host"
+	staticAssetPath = "/static/"
 )
 
-var apiPattern = regexp.MustCompile(`^/v\d+/`)
+var (
+	apiPattern         = regexp.MustCompile(`^/v\d+/`)
+	staticRoutePattern = regexp.MustCompile(`^/static*`)
+)
 
 type assetHandler struct {
 	assetCfg *gatewayv1.Assets
@@ -76,10 +80,17 @@ func (a *assetHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	// Set the original path.
 	r.URL.Path = origPath
 
+	// if enableStaticBaseRoute is set to true, we wont attempt to serve assets if there is no extension in the path.
+	// This is to prevent serving the SPA when the user is trying to access a nested route.
+	if a.isStaticPathRoutable(r.URL.Path) {
+		r.URL.Path = "/"
+		a.fileServer.ServeHTTP(w, r)
+	}
+
 	// Serve!
 	if f, err := a.fileSystem.Open(r.URL.Path); err != nil {
 		// If not a known static asset and an asset provider is configured, try streaming from the configured provider.
-		if a.assetCfg != nil && a.assetCfg.Provider != nil && strings.HasPrefix(r.URL.Path, "/static/") {
+		if a.assetCfg != nil && a.assetCfg.Provider != nil && strings.HasPrefix(r.URL.Path, staticAssetPath) {
 			// We attach this header simply for observability purposes.
 			// Otherwise its difficult to know if the assets are being served from the configured provider.
 			w.Header().Set("x-clutch-asset-passthrough", "true")
@@ -110,6 +121,15 @@ func (a *assetHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	a.fileServer.ServeHTTP(w, r)
 }
 
+func (a *assetHandler) isStaticPathRoutable(urlPath string) bool {
+	if a.assetCfg != nil && a.assetCfg.RoutableStaticPath {
+		// If the path is the base route, we need to serve the SPA.
+		return staticRoutePattern.MatchString(urlPath) && path.Ext(urlPath) == "" && urlPath != "/"
+	}
+
+	return false
+}
+
 func (a *assetHandler) assetProviderHandler(ctx context.Context, urlPath string) (io.ReadCloser, error) {
 	switch a.assetCfg.Provider.(type) {
 	case *gatewayv1.Assets_S3:

backend/gateway/mux/mux_test.go

@@ -235,3 +235,67 @@ func TestCustomResponseForwarderAuthCookiesNonBrowser(t *testing.T) {
 	assert.Equal(t, 200, rec.Code)
 	assert.Equal(t, "", rec.Header().Get("Location"))
 }
+
+func TestRoutableStaticPathEnabled(t *testing.T) {
+	assetHandler := &assetHandler{
+		assetCfg: &gatewayv1.Assets{
+			RoutableStaticPath: true,
+		},
+	}
+
+	testCases := []struct {
+		id       string
+		urlPath  string
+		expected bool
+	}{
+		{
+			id:       "should not route /",
+			urlPath:  "/",
+			expected: false,
+		},
+		{
+			id:       "should route static assets",
+			urlPath:  "/static/main.js",
+			expected: false,
+		},
+		{
+			id:       "should route static assets",
+			urlPath:  "/static/main.css",
+			expected: false,
+		},
+		{
+			id:       "should serve the base route",
+			urlPath:  "/static",
+			expected: true,
+		},
+		{
+			id:       "should serve the base route with a trailing slash",
+			urlPath:  "/static/",
+			expected: true,
+		},
+		{
+			id:       "should serve the base route with longer paths",
+			urlPath:  "/static/hello",
+			expected: true,
+		},
+		{
+			id:       "should serve the base route with query params",
+			urlPath:  "/static/hello?foo=bar",
+			expected: true,
+		},
+		{
+			id:       "should not route apis",
+			urlPath:  "/v1/getstatic/hello",
+			expected: false,
+		},
+		{
+			id:       "should not route apis",
+			urlPath:  "/v1/staticapi/hello",
+			expected: false,
+		},
+	}
+
+	for _, test := range testCases {
+		assert.Equal(t, test.expected, assetHandler.isStaticPathRoutable(test.urlPath), test.id)
+	}
+}