fix: binary-safe canvas read via Upstash base64 encoding

Use path-based REST API with Upstash-Encoding: base64 header for
GETRANGE to prevent binary data corruption through JSON text encoding.
Verified all 32 colors round-trip correctly.

src/lib/canvas-storage.js

@@ -1,4 +1,4 @@
-import { getRedis, redisRaw } from './redis-client.js';
+import { redisRaw, redisRawBinary } from './redis-client.js';
 import { CANVAS_WIDTH, TOTAL_PIXELS, BITS_PER_PIXEL, REDIS_CANVAS_KEY } from './constants.js';
 
 /** Total bytes needed for the canvas bitfield */
@@ -6,55 +6,42 @@ const CANVAS_BYTES = Math.ceil((TOTAL_PIXELS * BITS_PER_PIXEL) / 8);
 
 /**
  * Get the full canvas as a Uint8Array of raw bytes.
- * Uses GETRANGE to fetch raw binary reliably (avoids encoding issues with GET).
+ * Uses raw REST API to avoid SDK binary encoding corruption.
  * Returns a zero-filled buffer if canvas doesn't exist yet.
  * @param {object} env
  * @returns {Promise<Uint8Array>}
  */
 export async function getFullCanvas(env) {
-  const redis = getRedis(env);
+  // Use base64 encoding for binary-safe transport of BITFIELD data
+  const base64 = await redisRawBinary(env, ['GETRANGE', REDIS_CANVAS_KEY, '0', String(CANVAS_BYTES - 1)]);
 
-  // Use GETRANGE to fetch the full string as raw bytes
-  // This is more reliable than GET for binary data written by BITFIELD
-  const data = await redis.getrange(REDIS_CANVAS_KEY, 0, CANVAS_BYTES - 1);
-  if (!data || data.length === 0) {
+  if (!base64 || base64.length === 0) {
     return new Uint8Array(CANVAS_BYTES);
   }
 
-  // Upstash REST may return base64 or raw string for binary data
-  if (typeof data === 'string') {
-    let raw;
-    try {
-      raw = atob(data);
-    } catch {
-      raw = data; // Already a raw string
-    }
-    const bytes = new Uint8Array(raw.length);
-    for (let i = 0; i < raw.length; i++) {
-      bytes[i] = raw.charCodeAt(i);
-    }
-    // Pad to full canvas size if shorter
-    if (bytes.length < CANVAS_BYTES) {
-      const padded = new Uint8Array(CANVAS_BYTES);
-      padded.set(bytes);
-      return padded;
-    }
-    return bytes;
+  const raw = atob(base64);
+  const bytes = new Uint8Array(raw.length);
+  for (let i = 0; i < raw.length; i++) {
+    bytes[i] = raw.charCodeAt(i);
   }
 
-  return new Uint8Array(CANVAS_BYTES);
+  if (bytes.length < CANVAS_BYTES) {
+    const padded = new Uint8Array(CANVAS_BYTES);
+    padded.set(bytes);
+    return padded;
+  }
+  return bytes;
 }
 
 /**
  * Set multiple pixels in a single atomic BITFIELD command.
- * Uses Upstash's builder pattern: redis.bitfield(key).set().set().exec()
+ * Uses raw REST API — SDK bitfield builder is broken in @upstash/redis 1.x.
  * @param {object} env
  * @param {Array<{x: number, y: number, color: number}>} pixels
  */
 export async function setPixels(env, pixels) {
   if (!pixels.length) return;
 
-  // Use raw REST API for BITFIELD — SDK builder API is broken in @upstash/redis 1.x
   const command = ['BITFIELD', REDIS_CANVAS_KEY];
   for (const { x, y, color } of pixels) {
     const offset = y * CANVAS_WIDTH + x;

src/lib/redis-client.js

@@ -33,3 +33,26 @@ export async function redisRaw(env, command) {
   }
   return res.json();
 }
+
+/**
+ * Execute a Redis command via Upstash path-based REST API with base64 response.
+ * Uses Upstash-Encoding: base64 for binary-safe response transport.
+ * @param {object} env
+ * @param {string[]} command - Redis command as array, e.g. ['GETRANGE', 'key', '0', '100']
+ * @returns {Promise<string|null>} base64-encoded result string
+ */
+export async function redisRawBinary(env, command) {
+  const path = command.map((arg) => encodeURIComponent(String(arg))).join('/');
+  const res = await fetch(`${env.UPSTASH_REDIS_REST_URL}/${path}`, {
+    headers: {
+      Authorization: `Bearer ${env.UPSTASH_REDIS_REST_TOKEN}`,
+      'Upstash-Encoding': 'base64',
+    },
+  });
+  if (!res.ok) {
+    const text = await res.text();
+    throw new Error(`Redis command failed: ${res.status} ${text}`);
+  }
+  const { result } = await res.json();
+  return result; // base64-encoded string
+}