Initial Commit

server/utils/linkPreview.ts

@@ -0,0 +1,58 @@
+const MAX_HTML_BYTES = 512 * 1024
+
+function metaContent(html: string, keys: string[]): string | null {
+  for (const key of keys) {
+    const escaped = key.replace(/[.*+?^${}()|[\]\\]/g, '\\$&')
+    const before = new RegExp(`<meta[^>]+(?:property|name)=["']${escaped}["'][^>]+content=["']([^"']+)["']`, 'i')
+    const after = new RegExp(`<meta[^>]+content=["']([^"']+)["'][^>]+(?:property|name)=["']${escaped}["']`, 'i')
+    const match = before.exec(html) ?? after.exec(html)
+    if (match?.[1]?.trim()) return match[1].trim()
+  }
+  return null
+}
+
+export interface LinkPreview {
+  image: string | null
+  title: string | null
+}
+
+const BLOCKED_HOST = /^(localhost|127\.|0\.0\.0\.0|::1|\[::1\]|169\.254\.|10\.|192\.168\.|172\.(1[6-9]|2\d|3[01])\.|.*\.(local|internal|lan)$)/i
+
+export function isBlockedHost(hostname: string): boolean {
+  return BLOCKED_HOST.test(hostname)
+}
+
+export async function fetchLinkPreview(url: string): Promise<LinkPreview> {
+  try {
+    const hostname = new URL(url).hostname
+    if (isBlockedHost(hostname)) return { image: null, title: null }
+    const res = await fetch(url, {
+      signal: AbortSignal.timeout(5000),
+      redirect: 'follow',
+      headers: {
+        'user-agent': 'Mozilla/5.0 (compatible; 4Brett-LinkPreview/1.0)',
+        'accept': 'text/html,application/xhtml+xml',
+      },
+    })
+    if (!res.ok) return { image: null, title: null }
+    const contentType = res.headers.get('content-type') ?? ''
+    if (!contentType.includes('text/html') && !contentType.includes('application/xhtml')) {
+      return { image: null, title: null }
+    }
+    const html = (await res.text()).slice(0, MAX_HTML_BYTES)
+    const base = res.url || url
+
+    const image = metaContent(html, ['og:image', 'og:image:url', 'og:image:secure_url', 'twitter:image', 'twitter:image:src'])
+    const title = metaContent(html, ['og:title', 'twitter:title'])
+      ?? /<title[^>]*>([^<]+)<\/title>/i.exec(html)?.[1]?.trim()
+      ?? null
+
+    return {
+      image: image ? new URL(image, base).href.slice(0, 2048) : null,
+      title: title?.slice(0, 500) ?? null,
+    }
+  }
+  catch {
+    return { image: null, title: null }
+  }
+}