Normalize double slashes in incoming locations

.changeset/selfish-fishes-push.md

@@ -0,0 +1,5 @@
+---
+"@remix-run/router": patch
+---
+
+Normalize double slashes in incoming locations

packages/react-router-dom/__tests__/data-browser-router-test.tsx

@@ -7542,6 +7542,41 @@ function testDomRouter(
       });
     });
   });
+
+  if (name === "<DataBrowserRouter>") {
+    describe("DataBrowserRouter-only tests", () => {
+      it("is defensive against double slash URLs in window.location", async () => {
+        let testWindow = getWindow("/a///b");
+        let router = createTestRouter(
+          [
+            {
+              path: "*",
+              Component() {
+                return <Link to="/page">Go to Page</Link>;
+              },
+            },
+            {
+              path: "/page",
+              Component() {
+                return <h1>Worked!</h1>;
+              },
+            },
+          ],
+          {
+            window: testWindow,
+          }
+        );
+        render(<RouterProvider router={router} />);
+        expect(testWindow.location.pathname).toBe("/a///b");
+        expect(router.state.location.pathname).toBe("/a/b");
+
+        fireEvent.click(screen.getByText("Go to Page"));
+        await waitFor(() => screen.getByText("Worked!"));
+        expect(testWindow.location.pathname).toBe("/page");
+        expect(router.state.location.pathname).toBe("/page");
+      });
+    });
+  }
 }
 
 function getWindowImpl(initialUrl: string, isHash = false): Window {

packages/router/history.ts

@@ -527,6 +527,10 @@ function getHistoryState(location: Location, index: number): HistoryState {
   };
 }
 
+function normalizeMultipleSlashes(path: string) {
+  return path.replace(/\/{2,}/g, "/");
+}
+
 /**
  * Creates a Location object with a unique key from the given Path
  */
@@ -536,11 +540,17 @@ export function createLocation(
   state: any = null,
   key?: string
 ): Readonly<Location> {
+  let toLocation = typeof to === "string" ? parsePath(to) : to;
+  if (toLocation.pathname) {
+    toLocation.pathname = normalizeMultipleSlashes(toLocation.pathname);
+  }
   let location: Readonly<Location> = {
-    pathname: typeof current === "string" ? current : current.pathname,
+    pathname: normalizeMultipleSlashes(
+      typeof current === "string" ? current : current.pathname
+    ),
     search: "",
     hash: "",
-    ...(typeof to === "string" ? parsePath(to) : to),
+    ...toLocation,
     state,
     // TODO: This could be cleaned up.  push/replace should probably just take
     // full Locations now and avoid the need to run through this flow at all
@@ -586,7 +596,7 @@ export function parsePath(path: string): Partial<Path> {
     }
 
     if (path) {
-      parsedPath.pathname = path;
+      parsedPath.pathname = normalizeMultipleSlashes(path);
     }
   }
 

packages/router/router.ts

@@ -1637,7 +1637,7 @@ export function createRouter(init: RouterInit): Router {
       // Create a GET request for the loaders
       request = createClientSideRequest(
         init.history,
-        request.url,
+        createPath(new URL(request.url)),
         request.signal
       );
     }