feat(media): constants and markdown/cover URL extraction

Made-with: Cursor

server/constants/media.ts

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+/** 与 `upload` 返回及静态路径一致，无前导 host */
+export const POST_MEDIA_PUBLIC_PREFIX = "/public/assets/";
+
+/** 从未引用：created_at 起算；曾引用：dereferenced_at 起算 */
+export const MEDIA_ORPHAN_GRACE_HOURS_NEVER_REF = 24;
+export const MEDIA_ORPHAN_GRACE_HOURS_AFTER_DEREF = 24;
+
+export const MEDIA_IMAGE_MAX_WIDTH_PX = 1920;
+export const MEDIA_WEBP_QUALITY = 82;
+
+export const RELATIVE_ASSETS_DIR = "public/assets";

server/utils/post-media-urls.ts

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+import { POST_MEDIA_PUBLIC_PREFIX } from "#server/constants/media";
+
+const MD_IMG_RE = /!\[[^\]]*]\(([^)]+)\)/g;
+
+function normalizeUrl(raw: string): string {
+  const t = raw.trim().replace(/^<|>$/g, "").split(/\s+/)[0] ?? "";
+  if (t.startsWith(POST_MEDIA_PUBLIC_PREFIX)) {
+    return t;
+  }
+  return "";
+}
+
+/** 从 markdown 中提取本站图片 URL（去重，顺序稳定） */
+export function extractMediaUrlsFromMarkdown(markdown: string): string[] {
+  const out: string[] = [];
+  const seen = new Set<string>();
+  let m: RegExpExecArray | null;
+  const re = new RegExp(MD_IMG_RE.source, MD_IMG_RE.flags);
+  while ((m = re.exec(markdown)) !== null) {
+    const u = normalizeUrl(m[1] ?? "");
+    if (u && !seen.has(u)) {
+      seen.add(u);
+      out.push(u);
+    }
+  }
+  return out;
+}
+
+export function extractMediaUrlsFromCover(coverUrl: string | null | undefined): string[] {
+  if (!coverUrl) {
+    return [];
+  }
+  const u = normalizeUrl(coverUrl);
+  return u ? [u] : [];
+}
+
+export function mergePostMediaUrls(bodyMarkdown: string, coverUrl: string | null | undefined): string[] {
+  const a = extractMediaUrlsFromMarkdown(bodyMarkdown);
+  const b = extractMediaUrlsFromCover(coverUrl);
+  const seen = new Set<string>(a);
+  for (const u of b) {
+    if (!seen.has(u)) {
+      seen.add(u);
+      a.push(u);
+    }
+  }
+  return a;
+}
+
+/** `/public/assets/foo.webp` → `foo.webp` */
+export function publicAssetUrlToStorageKey(url: string): string | null {
+  const t = url.trim();
+  if (!t.startsWith(POST_MEDIA_PUBLIC_PREFIX)) {
+    return null;
+  }
+  const key = t.slice(POST_MEDIA_PUBLIC_PREFIX.length).replace(/^\/+/, "");
+  if (!key || key.includes("..") || key.includes("/") || key.includes("\\")) {
+    return null;
+  }
+  return key;
+}