chore: strict Subdomain Validation with Detailed Error Messages (#42)

Co-authored-by: userAdityaa <aditya.chaudhary1558@gmail.com>
Co-committed-by: userAdityaa <aditya.chaudhary1558@gmail.com>

frontend/src/components/RelayForm.tsx

@@ -1,6 +1,7 @@
 import { createEffect, createMemo, createSignal, For } from "solid-js"
 import type { Relay } from "@/lib/hooks"
 import { slugify } from "@/lib/slugify"
+import { validateSubdomainLabel } from "@/lib/subdomain"
 import { setToastMessage } from "@/components/Toast"
 import { plans } from "@/lib/state"
 
@@ -31,6 +32,12 @@ export default function RelayForm(props: RelayFormProps) {
       return
     }
 
+    const subdomainError = validateSubdomainLabel(subdomain())
+    if (subdomainError) {
+      setToastMessage(subdomainError)
+      return
+    }
+
     setToastMessage("")
     setSubmitting(true)
 

frontend/src/lib/subdomain.ts

@@ -0,0 +1,22 @@
+const SUBDOMAIN_LABEL_MAX_LEN = 63
+const RESERVED_SUBDOMAIN_LABELS = new Set(["api", "admin"])
+
+export function validateSubdomainLabel(subdomain: string): string | null {
+  if (subdomain.length === 0) {
+    return "subdomain is required"
+  }
+  if (subdomain.length > SUBDOMAIN_LABEL_MAX_LEN) {
+    return "subdomain must be 63 characters or fewer"
+  }
+  if (subdomain.startsWith("-") || subdomain.endsWith("-")) {
+    return "subdomain cannot start or end with a hyphen"
+  }
+  if (RESERVED_SUBDOMAIN_LABELS.has(subdomain)) {
+    return "subdomain is reserved"
+  }
+  if (!/^[a-z0-9-]+$/.test(subdomain)) {
+    return "subdomain may only contain lowercase letters, numbers, and hyphens"
+  }
+
+  return null
+}

frontend/src/pages/relays/RelayEdit.tsx

@@ -1,7 +1,6 @@
 import { useNavigate, useParams } from "@solidjs/router"
 import { Show } from "solid-js"
 import RelayForm, { type RelayFormValues } from "@/components/RelayForm"
-import { slugify } from "@/lib/slugify"
 import BackLink from "@/components/BackLink"
 import PageContainer from "@/components/PageContainer"
 import ResourceState from "@/components/ResourceState"
@@ -18,7 +17,7 @@ export default function RelayEdit(props: { basePath?: string; title?: string })
 
   async function handleSubmit(values: RelayFormValues) {
     await updateRelayById(relayId(), {
-      subdomain: slugify(values.subdomain),
+      subdomain: values.subdomain,
       info_name: values.info_name.trim(),
       info_icon: values.info_icon.trim(),
       info_description: values.info_description.trim(),