[fix] consider protocol-relative URLs as external (#2062)

Author: benmccann

.changeset/wet-lemons-cheat.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+[fix] consider protocol-relative URLs as external

packages/kit/src/core/adapt/prerender.js

@@ -246,7 +246,7 @@ export async function prerender({ cwd, out, log, config, build_data, fallback, a
 					if (!href) continue;
 
 					const resolved = resolve(path, href);
-					if (resolved[0] !== '/') continue;
+					if (!resolved.startsWith('/') || resolved.startsWith('//')) continue;
 
 					const parsed = new URL(resolved, 'http://localhost');
 

packages/kit/src/runtime/server/page/load_node.js

@@ -110,7 +110,7 @@ export async function load_node({
 								`http://${page.host}/${asset.file}`,
 								/** @type {RequestInit} */ (opts)
 						  );
-				} else if (resolved.startsWith(options.paths.base || '/')) {
+				} else if (resolved.startsWith(options.paths.base || '/') && !resolved.startsWith('//')) {
 					const relative = resolved.replace(options.paths.base, '');
 
 					const headers = /** @type {import('types/helper').Headers} */ ({ ...opts.headers });