1 files changed, 19 insertions, 0 deletions
diff --git a/packages/astro-rss/src/util.ts b/packages/astro-rss/src/util.ts
new file mode 100644
index 000000000..0dad6b239
--- /dev/null
+++ b/packages/astro-rss/src/util.ts
@@ -0,0 +1,19 @@
+import npath from 'path-browserify';
+
+/** Normalize URL to its canonical form */
+export function createCanonicalURL(url: string, base?: string): URL {
+	let pathname = url.replace(/\/index.html$/, ''); // index.html is not canonical
+	pathname = pathname.replace(/\/1\/?$/, ''); // neither is a trailing /1/ (impl. detail of collections)
+	if (!npath.extname(pathname)) pathname = pathname.replace(/(\/+)?$/, '/'); // add trailing slash if there’s no extension
+	pathname = pathname.replace(/\/+/g, '/'); // remove duplicate slashes (URL() won’t)
+	return new URL(pathname, base);
+}
+
+/** Check if a URL is already valid */
+export function isValidURL(url: string): boolean {
+	try {
+		new URL(url);
+		return true;
+	} catch (e) {}
+	return false;
+}