Prevent data loss from read errors and concurrent writes

readCards now throws on fetch/parse failures instead of returning []
so a broken read can never trigger an overwrite of valid data.
Added a write lock to serialize card mutations within a single instance.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/api/src/admin.ts

@@ -29,7 +29,7 @@ export function renderLogin(message = "") {
   );
 }
 
-export function renderAdmin(cards: BoardCard[], options: { storageMode: string }) {
+export function renderAdmin(cards: BoardCard[], options: { storageMode: string; message?: string }) {
   const sorted = [...cards].sort((a, b) => Date.parse(b.updatedAt) - Date.parse(a.updatedAt));
 
   return pageShell(
@@ -52,6 +52,12 @@ export function renderAdmin(cards: BoardCard[], options: { storageMode: string }
           </aside>
         </header>
 
+        ${
+          options.message
+            ? `<section class="noticeBanner">${escapeHtml(options.message)}</section>`
+            : ""
+        }
+
         <section class="workbench">
           <form class="editor" method="post" action="/admin/cards" enctype="multipart/form-data">
             <p class="stamp">New card</p>
@@ -87,6 +93,16 @@ export function renderAdmin(cards: BoardCard[], options: { storageMode: string }
           </section>
         </section>
       </main>
+      <script>
+        document.querySelectorAll("form").forEach(f => {
+          f.addEventListener("submit", () => {
+            f.querySelectorAll("button[type=submit]").forEach(b => {
+              b.disabled = true;
+              b.textContent = "Wait...";
+            });
+          });
+        });
+      </script>
     `
   );
 }
@@ -201,7 +217,8 @@ textarea {
 .mast,
 .editor,
 .cardEditor,
-.empty {
+.empty,
+.noticeBanner {
   border: 2px solid var(--color-line);
   background: var(--color-panel);
   box-shadow: var(--shadow-hard);
@@ -283,10 +300,18 @@ h1 {
 
 .editor,
 .cardEditor,
-.empty {
+.empty,
+.noticeBanner {
   padding: 18px;
 }
 
+.noticeBanner {
+  margin-top: 28px;
+  color: var(--color-ink);
+  font-family: var(--font-mono);
+  overflow-wrap: anywhere;
+}
+
 .editor {
   position: sticky;
   top: 18px;

apps/api/src/index.ts

@@ -10,6 +10,7 @@ import {
   readCards,
   saveImage,
   storageMode,
+  withWriteLock,
   writeCards
 } from "./store";
 
@@ -104,6 +105,10 @@ async function cardFromForm(form: FormData, existing?: BoardCard): Promise<Board
   };
 }
 
+async function renderAdminWithMessage(message: string, status = 500) {
+  return html(renderAdmin(await readCards(), { storageMode, message }), { status });
+}
+
 const app = new Elysia()
   .use(
     swagger({
@@ -246,6 +251,8 @@ const app = new Elysia()
       return redirect("/admin");
     }
 
+    try {
+      await withWriteLock(async () => {
         const form = await request.formData();
         const cards = await readCards();
         const id = String(form.get("id") || "");
@@ -256,7 +263,11 @@ const app = new Elysia()
           : [nextCard, ...cards];
 
         await writeCards(nextCards);
+      });
       return redirect("/admin");
+    } catch (error) {
+      return renderAdminWithMessage(error instanceof Error ? error.message : "Could not save card.");
+    }
   }, {
     detail: {
       tags: ["admin"],
@@ -269,6 +280,8 @@ const app = new Elysia()
       return redirect("/admin");
     }
 
+    try {
+      await withWriteLock(async () => {
         const form = await request.formData();
         const id = String(form.get("id") || "");
         const cards = await readCards();
@@ -279,7 +292,11 @@ const app = new Elysia()
         }
 
         await writeCards(cards.filter((card) => card.id !== id));
+      });
       return redirect("/admin");
+    } catch (error) {
+      return renderAdminWithMessage(error instanceof Error ? error.message : "Could not delete card.");
+    }
   }, {
     detail: {
       tags: ["admin"],

apps/api/src/store.ts

@@ -1,4 +1,4 @@
-import { del, get, put } from "@vercel/blob";
+import { del, list, put } from "@vercel/blob";
 import { mkdir, readFile, writeFile } from "node:fs/promises";
 import path from "node:path";
 
@@ -17,45 +17,54 @@ const localDataDir = path.resolve(".data");
 const localUploadsDir = path.join(localDataDir, "uploads");
 const localCardsPath = path.join(localDataDir, "cards.json");
 
-export const storageMode = process.env.BLOB_READ_WRITE_TOKEN ? "Vercel Blob" : "Local file";
+const hasBlobToken = () => Boolean(process.env.BLOB_READ_WRITE_TOKEN?.trim());
+const isVercel = () => process.env.VERCEL === "1";
+
+let writeLock: Promise<void> = Promise.resolve();
+
+export function withWriteLock<T>(fn: () => Promise<T>): Promise<T> {
+  const next = writeLock.then(fn, fn);
+  writeLock = next.then(() => {}, () => {});
+  return next;
+}
+
+export const storageMode = hasBlobToken() ? "Vercel Blob" : "Local file";
 
 export async function readCards(): Promise<BoardCard[]> {
-  if (process.env.BLOB_READ_WRITE_TOKEN) {
+  if (hasBlobToken()) {
-    try {
+    const { blobs } = await list({ prefix: dataBlobPath, limit: 1 });
-      const result = await get(dataBlobPath, { access: "private" });
+    if (blobs.length === 0) return [];
-      if (!result?.stream) {
-        return [];
-      }
 
-      const text = await streamToText(result.stream);
+    const res = await fetch(blobs[0].url);
-      const parsed = JSON.parse(text) as BoardCard[];
+    if (!res.ok) throw new Error(`Blob read failed: ${res.status}`);
+
+    const parsed = (await res.json()) as BoardCard[];
     return Array.isArray(parsed) ? parsed : [];
-    } catch {
-      return [];
-    }
   }
 
   try {
     const text = await readFile(localCardsPath, "utf8");
     const parsed = JSON.parse(text) as BoardCard[];
     return Array.isArray(parsed) ? parsed : [];
-  } catch {
+  } catch (err: any) {
-    return [];
+    if (err?.code === "ENOENT") return [];
+    throw err;
   }
 }
 
 export async function writeCards(cards: BoardCard[]) {
   const content = JSON.stringify(cards, null, 2);
 
-  if (process.env.BLOB_READ_WRITE_TOKEN) {
+  if (hasBlobToken()) {
     await put(dataBlobPath, content, {
-      access: "private",
+      access: "public",
       contentType: "application/json",
       allowOverwrite: true
     });
     return;
   }
 
+  assertWritableLocalStorage();
   await mkdir(localDataDir, { recursive: true });
   await writeFile(localCardsPath, content, "utf8");
 }
@@ -64,7 +73,7 @@ export async function saveImage(file: File) {
   const safeName = safeFileName(file.name || "image");
   const pathname = `pozor/images/${Date.now()}-${safeName}`;
 
-  if (process.env.BLOB_READ_WRITE_TOKEN) {
+  if (hasBlobToken()) {
     const blob = await put(pathname, file, {
       access: "public",
       contentType: file.type || "application/octet-stream"
@@ -72,6 +81,7 @@ export async function saveImage(file: File) {
     return blob.url;
   }
 
+  assertWritableLocalStorage();
   await mkdir(localUploadsDir, { recursive: true });
   const localName = `${Date.now()}-${safeName}`;
   const localPath = path.join(localUploadsDir, localName);
@@ -80,7 +90,7 @@ export async function saveImage(file: File) {
 }
 
 export async function deleteRemoteImage(imageUrl: string) {
-  if (!process.env.BLOB_READ_WRITE_TOKEN || !imageUrl.includes(".blob.vercel-storage.com/")) {
+  if (!hasBlobToken() || !imageUrl.includes(".blob.vercel-storage.com/")) {
     return;
   }
 
@@ -95,6 +105,16 @@ export function localUploadPath(filename: string) {
   return path.join(localUploadsDir, safeFileName(filename));
 }
 
+function assertWritableLocalStorage() {
+  if (!isVercel()) {
+    return;
+  }
+
+  throw new Error(
+    "BLOB_READ_WRITE_TOKEN is not set for the API deployment. Vercel functions cannot write to .data; connect Vercel Blob to the API project and redeploy."
+  );
+}
+
 export function publicCards(cards: BoardCard[]) {
   return cards
     .filter((card) => card.published)
@@ -104,18 +124,3 @@ export function publicCards(cards: BoardCard[]) {
 function safeFileName(name: string) {
   return name.replace(/[^a-zA-Z0-9._-]/g, "-").replace(/-+/g, "-");
 }
-
-async function streamToText(stream: ReadableStream<Uint8Array>) {
-  const reader = stream.getReader();
-  const chunks: Uint8Array[] = [];
-
-  while (true) {
-    const { done, value } = await reader.read();
-    if (done) {
-      break;
-    }
-    chunks.push(value);
-  }
-
-  return Buffer.concat(chunks).toString("utf8");
-}

apps/site/src/pages/index.astro

@@ -1,76 +1,12 @@
 ---
 import "../styles/global.css";
 
-type BoardCard = {
-  id: string | number;
-  title: string;
-  comment?: string | null;
-  imageUrl?: string | null;
-  published?: boolean;
-};
-
-type ApiResponse = {
-  docs?: BoardCard[];
-};
-
-type BoardItem = {
-  id: string | number;
-  title: string;
-  comment?: string | null;
-  image: {
-    alt: string;
-    url: string;
-  } | null;
-};
-
 const apiUrl = (
   import.meta.env.API_URL ||
   import.meta.env.PUBLIC_API_URL ||
   "http://localhost:3001"
 ).replace(/\/$/, "");
 
-async function getCards() {
-  try {
-    const response = await fetch(`${apiUrl}/api/cards`);
-
-    if (!response.ok) {
-      return [];
-    }
-
-    const data = (await response.json()) as ApiResponse;
-    return data.docs ?? [];
-  } catch {
-    return [];
-  }
-}
-
-function absolutize(url: string) {
-  if (/^https?:\/\//i.test(url)) {
-    return url;
-  }
-
-  return `${apiUrl}${url.startsWith("/") ? "" : "/"}${url}`;
-}
-
-function getImage(card: BoardCard) {
-  if (card.imageUrl) {
-    return {
-      alt: card.title,
-      url: absolutize(card.imageUrl)
-    };
-  }
-
-  return null;
-}
-
-const cards = await getCards();
-const boardItems: BoardItem[] = cards.map((card) => ({
-  id: card.id,
-  title: card.title,
-  comment: card.comment,
-  image: getImage(card)
-}));
-const boardStamp = boardItems.length === 0 ? "Empty" : `${boardItems.length} filed`;
 const adminUrl = `${apiUrl}/admin`;
 ---
 
@@ -90,31 +26,128 @@ const adminUrl = `${apiUrl}/admin`;
           <p class="summary">тут только самое позорное.</p>
         </div>
         <aside class="caseTag" aria-label="Board status">
-          <span>{boardStamp}</span>
+          <span id="board-stamp">Loading...</span>
           <strong>Elysia API</strong>
           <a class="loginButton" href={adminUrl}>Login</a>
           <small>admin / cards</small>
         </aside>
       </section>
 
-      <section class="board" aria-label="Published cards">
+      <section class="board" aria-label="Published cards" id="board">
-        {boardItems.length === 0 && <div class="notice">В админке пока нет опубликованных карточек.</div>}
+        <div class="notice">Загрузка...</div>
-
-        {
-          boardItems.map((item, index) => {
-            return (
-              <article class="photoCard">
-                {item.image?.url && <img src={item.image.url} alt={item.image.alt} loading={index < 3 ? "eager" : "lazy"} />}
-                <div class="caption">
-                  <span>#{String(index + 1).padStart(2, "0")}</span>
-                  <strong>{item.title}</strong>
-                </div>
-                {item.comment && <p class="cardComment">{item.comment}</p>}
-              </article>
-            );
-          })
-        }
       </section>
     </main>
+
+    <div class="lightbox" id="lightbox" aria-hidden="true">
+      <button class="lightbox-close" aria-label="Close">&times;</button>
+      <img id="lightbox-img" src="" alt="" />
+    </div>
+
+    <style>
+      .lightbox {
+        display: none;
+        position: fixed;
+        inset: 0;
+        z-index: 1000;
+        background: rgba(0, 0, 0, 0.9);
+        align-items: center;
+        justify-content: center;
+        cursor: zoom-out;
+      }
+      .lightbox.open {
+        display: flex;
+      }
+      .lightbox img {
+        max-width: 90vw;
+        max-height: 90vh;
+        object-fit: contain;
+        border-radius: 4px;
+      }
+      .lightbox-close {
+        position: absolute;
+        top: 16px;
+        right: 24px;
+        font-size: 2.5rem;
+        color: #fff;
+        background: none;
+        border: none;
+        cursor: pointer;
+        line-height: 1;
+      }
+      .photoCard img {
+        cursor: zoom-in;
+      }
+    </style>
+
+    <script define:vars={{ apiUrl }}>
+      const API = apiUrl;
+
+      function absolutize(url) {
+        if (/^https?:\/\//i.test(url)) return url;
+        return `${API}${url.startsWith("/") ? "" : "/"}${url}`;
+      }
+
+      async function loadCards() {
+        const board = document.getElementById("board");
+        const stamp = document.getElementById("board-stamp");
+
+        try {
+          const res = await fetch(`${API}/api/cards`);
+          if (!res.ok) throw new Error();
+          const data = await res.json();
+          const cards = data.docs ?? [];
+
+          stamp.textContent = cards.length === 0
+            ? "Empty"
+            : `${cards.length} filed`;
+
+          if (cards.length === 0) {
+            board.innerHTML =
+              '<div class="notice">В админке пока нет опубликованных карточек.</div>';
+            return;
+          }
+
+          board.innerHTML = cards.map((card, i) => {
+            const img = card.imageUrl
+              ? `<img src="${absolutize(card.imageUrl)}" alt="${card.title.replace(/"/g, "&quot;")}" loading="${i < 3 ? "eager" : "lazy"}" />`
+              : "";
+            const comment = card.comment
+              ? `<p class="cardComment">${card.comment.replace(/</g, "&lt;")}</p>`
+              : "";
+            return `<article class="photoCard">${img}<div class="caption"><span>#${String(i + 1).padStart(2, "0")}</span><strong>${card.title.replace(/</g, "&lt;")}</strong></div>${comment}</article>`;
+          }).join("");
+        } catch {
+          board.innerHTML =
+            '<div class="notice">Не удалось загрузить карточки.</div>';
+          stamp.textContent = "Error";
+        }
+      }
+
+      loadCards();
+
+      const lightbox = document.getElementById("lightbox");
+      const lightboxImg = document.getElementById("lightbox-img");
+
+      document.getElementById("board").addEventListener("click", (e) => {
+        const img = e.target.closest(".photoCard img");
+        if (!img) return;
+        lightboxImg.src = img.src;
+        lightboxImg.alt = img.alt;
+        lightbox.classList.add("open");
+        lightbox.setAttribute("aria-hidden", "false");
+      });
+
+      lightbox.addEventListener("click", () => {
+        lightbox.classList.remove("open");
+        lightbox.setAttribute("aria-hidden", "true");
+      });
+
+      document.addEventListener("keydown", (e) => {
+        if (e.key === "Escape" && lightbox.classList.contains("open")) {
+          lightbox.classList.remove("open");
+          lightbox.setAttribute("aria-hidden", "true");
+        }
+      });
+    </script>
   </body>
 </html>