url_util: Keep trailing slashes

And don't remove repeated slashes until they're at the end.

src/url_util.test.ts

@@ -61,17 +61,19 @@ function test_parent() {
         // single level path
         ["http://example.com/path", "http://example.com/"],
         // multi-level path
-        ["http://example.com/path1/path2", "http://example.com/path1"],
+        ["http://example.com/path1/path2", "http://example.com/path1/"],
+        ["http://example.com/path1/path2/path3", "http://example.com/path1/path2/"],
         // subdomains
         ["http://sub.example.com", "http://example.com/"],
         // subdom with path, leave subdom
         ["http://sub.example.com/path", "http://sub.example.com/"],
         // trailing slash
         ["http://sub.example.com/path/", "http://sub.example.com/"],
+        ["http://sub.example.com/path/to/", "http://sub.example.com/path/"],
         // repeated slash
         ["http://example.com/path//", "http://example.com/"],
-        // repeated slash
-        ["http://example.com//path//", "http://example.com/"],
+        ["http://example.com//path//", "http://example.com//"],
+        ["http://example.com//path//", "http://example.com//"],
     ]
 
     for (let [url, exp_parent] of cases) {

src/url_util.ts

@@ -78,13 +78,10 @@ export function getUrlParent(url, count = 1) {
             return gup(parent, count - 1)
         }
 
-        // pathname always starts '/'
+        // empty path is '/'
         if (parent.pathname !== '/') {
-            // Split on '/' and remove empty substrings
-            // (handles initial and trailing slashes, repeated slashes, etc.)
-            let path = parent.pathname.split('/').filter(sub => sub !== "")
-            path.pop()
-            parent.pathname = path.join('/')
+            // Remove trailing slashes and everything to the next slash:
+            parent.pathname = parent.pathname.replace(/\/[^\/]*?\/*$/, '/')
             return gup(parent, count - 1)
         }