1 files changed, 53 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..43de370dd
--- /dev/null
+++ b/packages/astro-rss/src/util.ts
@@ -0,0 +1,53 @@
+import type { z } from 'astro/zod';
+import type { RSSOptions } from './index.js';
+
+/** Normalize URL to its canonical form */
+export function createCanonicalURL(
+	url: string,
+	trailingSlash?: RSSOptions['trailingSlash'],
+	base?: string,
+): string {
+	let pathname = url.replace(/\/index.html$/, ''); // index.html is not canonical
+	if (!getUrlExtension(url)) {
+		// add trailing slash if there’s no extension or `trailingSlash` is true
+		pathname = pathname.replace(/\/*$/, '/');
+	}
+
+	pathname = pathname.replace(/\/+/g, '/'); // remove duplicate slashes (URL() won’t)
+
+	const canonicalUrl = new URL(pathname, base).href;
+	if (trailingSlash === false) {
+		// remove the trailing slash
+		return canonicalUrl.replace(/\/*$/, '');
+	}
+	return canonicalUrl;
+}
+
+/** Check if a URL is already valid */
+export function isValidURL(url: string): boolean {
+	try {
+		new URL(url);
+		return true;
+	} catch {}
+	return false;
+}
+
+function getUrlExtension(url: string) {
+	const lastDot = url.lastIndexOf('.');
+	const lastSlash = url.lastIndexOf('/');
+	return lastDot > lastSlash ? url.slice(lastDot + 1) : '';
+}
+
+const flattenErrorPath = (errorPath: (string | number)[]) => errorPath.join('.');
+
+export const errorMap: z.ZodErrorMap = (error, ctx) => {
+	if (error.code === 'invalid_type') {
+		const badKeyPath = JSON.stringify(flattenErrorPath(error.path));
+		if (error.received === 'undefined') {
+			return { message: `${badKeyPath} is required.` };
+		} else {
+			return { message: `${badKeyPath} should be ${error.expected}, not ${error.received}.` };
+		}
+	}
+	return { message: ctx.defaultError };
+};