Fix path traversal bug in router (#2398)

* fix path traversal bug in router

Signed-off-by: Jari Kolehmainen <jari.kolehmainen@gmail.com>

* add tests

Signed-off-by: Jari Kolehmainen <jari.kolehmainen@gmail.com>

src/main/__test__/router.test.ts

@@ -0,0 +1,40 @@
+import { Router } from "../router";
+
+const staticRoot = __dirname;
+
+class TestRouter extends Router {
+  protected resolveStaticRootPath() {
+    return staticRoot;
+  }
+}
+
+describe("Router", () => {
+  it("blocks path traversal attacks", async () => {
+    const router = new TestRouter();
+    const res = {
+      statusCode: 200,
+      end: jest.fn()
+    };
+
+    await router.handleStaticFile("../index.ts", res as any, {} as any, 0);
+
+    expect(res.statusCode).toEqual(404);
+  });
+
+  it("serves files under static root", async () => {
+    const router = new TestRouter();
+    const res = {
+      statusCode: 200,
+      write: jest.fn(),
+      setHeader: jest.fn(),
+      end: jest.fn()
+    };
+    const req = {
+      url: ""
+    };
+
+    await router.handleStaticFile("router.test.ts", res as any, req as any, 0);
+
+    expect(res.statusCode).toEqual(200);
+  });
+});