cache failed favicons

src/components/Favicon/index.tsx

@@ -1,3 +1,4 @@
+import { isFaviconLoadFailed, markFaviconLoadFailed, normalizeFaviconDomain } from '@/lib/favicon-fail-cache'
 import { cn } from '@/lib/utils'
 import { useState } from 'react'
 
@@ -10,19 +11,23 @@ export function Favicon({
   className?: string
   fallback?: React.ReactNode
 }) {
-  const [loading, setLoading] = useState(true)
-  const [error, setError] = useState(false)
-  const trimmed = domain?.trim() ?? ''
-  if (error || !trimmed) return fallback
+  const host = normalizeFaviconDomain(domain)
+  const knownFailed = host ? isFaviconLoadFailed(host) : true
+  const [loading, setLoading] = useState(!knownFailed)
+  const [error, setError] = useState(knownFailed)
+  if (error || !host) return fallback
 
   return (
     <div className={cn('relative', className)}>
       {loading && <div className={cn('absolute inset-0', className)}>{fallback}</div>}
       <img
-        src={`https://${trimmed}/favicon.ico`}
-        alt={trimmed}
+        src={`https://${host}/favicon.ico`}
+        alt={host}
         className={cn('absolute inset-0', loading && 'opacity-0', className)}
-        onError={() => setError(true)}
+        onError={() => {
+          markFaviconLoadFailed(host)
+          setError(true)
+        }}
         onLoad={() => setLoading(false)}
       />
     </div>

src/lib/favicon-fail-cache.test.ts

@@ -0,0 +1,20 @@
+import { describe, expect, it } from 'vitest'
+import {
+  isFaviconLoadFailed,
+  markFaviconLoadFailed,
+  normalizeFaviconDomain
+} from '@/lib/favicon-fail-cache'
+
+describe('favicon-fail-cache', () => {
+  it('normalizes domain casing and trailing dot', () => {
+    expect(normalizeFaviconDomain(' Example.COM. ')).toBe('example.com')
+  })
+
+  it('remembers failed domains for the session', () => {
+    const host = `fail-cache-test-${Date.now()}.example`
+    expect(isFaviconLoadFailed(host)).toBe(false)
+    markFaviconLoadFailed(host)
+    expect(isFaviconLoadFailed(host)).toBe(true)
+    expect(isFaviconLoadFailed(host.toUpperCase())).toBe(true)
+  })
+})

src/lib/favicon-fail-cache.ts

@@ -0,0 +1,20 @@
+import { LRUCache } from 'lru-cache'
+
+/** Domains whose `https://{host}/favicon.ico` already failed — skip repeat network requests. */
+const FAILED_FAVICON_DOMAINS = new LRUCache<string, true>({ max: 512 })
+
+export function normalizeFaviconDomain(domain: string): string {
+  return domain.trim().toLowerCase().replace(/\.$/, '')
+}
+
+export function isFaviconLoadFailed(domain: string): boolean {
+  const key = normalizeFaviconDomain(domain)
+  if (!key) return true
+  return FAILED_FAVICON_DOMAINS.has(key)
+}
+
+export function markFaviconLoadFailed(domain: string): void {
+  const key = normalizeFaviconDomain(domain)
+  if (!key) return
+  FAILED_FAVICON_DOMAINS.set(key, true)
+}