initial commit

lib/validation.ts

@@ -0,0 +1,30 @@
+export const RESERVED_SUBDOMAINS = new Set([
+  'app',
+  'api',
+  'www',
+  'admin',
+  'auth',
+  'mail',
+  'static',
+]);
+
+const SUBDOMAIN_RE = /^[a-z0-9-]{3,32}$/;
+
+export function validateSubdomain(input: unknown):
+  | { ok: true; value: string }
+  | { ok: false; error: string } {
+  if (typeof input !== 'string') {
+    return { ok: false, error: 'subdomain must be a string' };
+  }
+  const value = input.trim().toLowerCase();
+  if (!SUBDOMAIN_RE.test(value)) {
+    return {
+      ok: false,
+      error: 'subdomain must be 3–32 chars, lowercase a–z, 0–9, hyphen',
+    };
+  }
+  if (RESERVED_SUBDOMAINS.has(value)) {
+    return { ok: false, error: `'${value}' is reserved` };
+  }
+  return { ok: true, value };
+}