feat: best-effort artwork disk cache

server/src/artwork.ts

@@ -0,0 +1,41 @@
+import { createHash } from 'node:crypto'
+import { existsSync, mkdirSync } from 'node:fs'
+import { writeFile } from 'node:fs/promises'
+import path from 'node:path'
+
+const EXT_BY_TYPE: Record<string, string> = {
+  'image/jpeg': '.jpg',
+  'image/png': '.png',
+  'image/webp': '.webp',
+  'image/gif': '.gif',
+}
+
+/**
+ * Downloads `url` into `artworkDir` keyed by its sha256 hash. Returns the
+ * stored file name (e.g. `abc123….jpg`) or null when the url is empty or the
+ * download fails — artwork caching is best-effort and must never break adds.
+ */
+export async function cacheArtwork(
+  artworkDir: string,
+  url: string,
+  fetchImpl: typeof fetch = fetch
+): Promise<string | null> {
+  if (!url) return null
+  const key = createHash('sha256').update(url).digest('hex')
+  mkdirSync(artworkDir, { recursive: true })
+  for (const ext of Object.values(EXT_BY_TYPE)) {
+    if (existsSync(path.join(artworkDir, key + ext))) return key + ext
+  }
+  let res: Response
+  try {
+    res = await fetchImpl(url)
+  } catch {
+    return null
+  }
+  if (!res.ok) return null
+  const type = (res.headers.get('content-type') ?? '').split(';')[0]?.trim() ?? ''
+  const ext = EXT_BY_TYPE[type] ?? '.jpg'
+  const buf = Buffer.from(await res.arrayBuffer())
+  await writeFile(path.join(artworkDir, key + ext), buf)
+  return key + ext
+}