websites/packages/sanity-cms/schemas/fields/basic/url.ts

import { defineField } from 'sanity';

const checkedUrlResults = new Map<string, string | true>();

export const urlField = defineField({
  name: 'url',
  type: 'url',
  title: 'URL',
  description:
    'An external link. If you want to link to an internal link (page or blog post), you must use a reference.',
  validation: (Rule) =>
    Rule.uri({ scheme: ['http', 'https', 'mailto'], allowRelative: false })
      .custom((url) => {
        if (!url) return true;

        const cachedResult = checkedUrlResults.get(url);
        if (cachedResult !== undefined) return cachedResult;

        if (url.startsWith('mailto:')) {
          // biome-ignore lint/performance/useTopLevelRegex: TODO: investigate regex warning
          const validEmail = /^[^\s@]+@[^\s@]+\.[^\s@]+$/.exec(url.replace('mailto:', ''));
          checkedUrlResults.set(url, validEmail ? true : 'Invalid email');
          return validEmail ? true : 'Invalid email';
        }

        return fetch(`/api/validate-url/${encodeURIComponent(url)}`).then((res) => {
          const val = res.ok ? true : res.statusText;
          checkedUrlResults.set(url, val);
          return val;
        });
      })
      .warning(),
});