fix: More flexible link validation in editor allows custom protocols

closes #4319

shared/utils/urls.ts

@@ -45,10 +45,11 @@ export function isInternalUrl(href: string) {
 /**
  * Returns true if the given string is a url.
  *
- * @param url The url to check.
+ * @param text The url to check.
+ * @param options Parsing options.
  * @returns True if a url, false otherwise.
  */
-export function isUrl(text: string) {
+export function isUrl(text: string, options?: { requireHostname: boolean }) {
   if (text.match(/\n/)) {
     return false;
   }
@@ -57,7 +58,18 @@ export function isUrl(text: string) {
     const url = new URL(text);
     const blockedProtocols = ["javascript:", "file:", "vbscript:", "data:"];
 
-    return url.hostname !== "" && !blockedProtocols.includes(url.protocol);
+    if (blockedProtocols.includes(url.protocol)) {
+      return false;
+    }
+    if (url.hostname) {
+      return true;
+    }
+
+    return (
+      url.protocol !== "" &&
+      url.pathname.startsWith("//") &&
+      !options?.requireHostname
+    );
   } catch (err) {
     return false;
   }
@@ -86,7 +98,7 @@ export function sanitizeUrl(url: string | null | undefined) {
   }
 
   if (
-    !isUrl(url) &&
+    !isUrl(url, { requireHostname: false }) &&
     !url.startsWith("/") &&
     !url.startsWith("#") &&
     !url.startsWith("mailto:") &&