Reject wallpaper captures for stickers

worker/src/server.js

@@ -1378,6 +1378,88 @@ async function downloadDomStickerThroughScreenshot(p, request) {
       buffer: dataUrl.startsWith(prefix) ? Buffer.from(dataUrl.slice(prefix.length), "base64") : null
     };
   };
+  const inspectStickerPng = async (buffer) => {
+    const base64 = buffer.toString("base64");
+    return await p.evaluate(async (dataUrl) => {
+      const image = new Image();
+      image.src = dataUrl;
+      await image.decode();
+
+      const canvas = document.createElement("canvas");
+      canvas.width = image.naturalWidth;
+      canvas.height = image.naturalHeight;
+      const context = canvas.getContext("2d", { willReadFrequently: true });
+      if (!context || canvas.width <= 0 || canvas.height <= 0) {
+        return null;
+      }
+
+      context.drawImage(image, 0, 0);
+      const data = context.getImageData(0, 0, canvas.width, canvas.height).data;
+      const totalPixels = canvas.width * canvas.height;
+      const step = Math.max(1, Math.floor(totalPixels / 20000));
+      let sampled = 0;
+      let opaque = 0;
+      let dark = 0;
+      let white = 0;
+      let cyan = 0;
+      let sumR = 0;
+      let sumG = 0;
+      let sumB = 0;
+
+      for (let pixel = 0; pixel < totalPixels; pixel += step) {
+        const offset = pixel * 4;
+        const r = data[offset];
+        const g = data[offset + 1];
+        const b = data[offset + 2];
+        const a = data[offset + 3];
+        sampled++;
+        if (a <= 8) {
+          continue;
+        }
+
+        opaque++;
+        sumR += r;
+        sumG += g;
+        sumB += b;
+        if (Math.max(r, g, b) < 95) dark++;
+        if (Math.min(r, g, b) > 230) white++;
+        if (b > r + 25 && g > r + 20 && b > 150 && g > 130) cyan++;
+      }
+
+      return {
+        width: canvas.width,
+        height: canvas.height,
+        sampled,
+        opaqueRatio: sampled ? opaque / sampled : 0,
+        darkRatio: opaque ? dark / opaque : 0,
+        whiteRatio: opaque ? white / opaque : 0,
+        cyanRatio: opaque ? cyan / opaque : 0,
+        avgR: opaque ? sumR / opaque : 0,
+        avgG: opaque ? sumG / opaque : 0,
+        avgB: opaque ? sumB / opaque : 0
+      };
+    }, `data:image/png;base64,${base64}`).catch(() => null);
+  };
+  const isMaxWallpaperCapture = (metrics) => {
+    if (!metrics) {
+      return false;
+    }
+
+    return metrics.opaqueRatio > 0.98 &&
+      metrics.cyanRatio > 0.72 &&
+      metrics.darkRatio < 0.03 &&
+      metrics.whiteRatio < 0.08 &&
+      metrics.avgB > metrics.avgR + 45 &&
+      metrics.avgG > metrics.avgR + 30;
+  };
+  const stickerCaptureResult = async (buffer) => {
+    const metrics = await inspectStickerPng(buffer);
+    if (isMaxWallpaperCapture(metrics)) {
+      throw new Error(`${kindLabel} capture matched MAX chat wallpaper instead of sticker.`);
+    }
+
+    return { contentType: "image/png", buffer };
+  };
   const screenshotCandidate = async (handles, requestedIndex) => {
     const candidates = [];
     for (const handle of handles) {
@@ -1522,7 +1604,7 @@ async function downloadDomStickerThroughScreenshot(p, request) {
       await target.handle.scrollIntoViewIfNeeded({ timeout: 3000 }).catch(() => {});
       const canvasCapture = await captureCanvasPng(target.handle);
       if (canvasCapture.buffer) {
-        return { contentType: "image/png", buffer: canvasCapture.buffer };
+        return await stickerCaptureResult(canvasCapture.buffer);
       }
 
       let buffer;
@@ -1548,7 +1630,7 @@ async function downloadDomStickerThroughScreenshot(p, request) {
           throw error;
         }
       }
-      return { contentType: "image/png", buffer };
+      return await stickerCaptureResult(buffer);
     } finally {
       for (const item of candidates) {
         await item.handle.dispose().catch(() => {});