Update decoder to correctly handle grayscale PNGs

packages/next/next-server/server/lib/squoosh/png/squoosh_png.js

@@ -1,5 +1,29 @@
+import { TextDecoder } from '../text-decoder'
+
 let wasm
 
+let cachedTextDecoder = new TextDecoder('utf-8', {
+  ignoreBOM: true,
+  fatal: true,
+})
+
+cachedTextDecoder.decode()
+
+let cachegetUint8Memory0 = null
+function getUint8Memory0() {
+  if (
+    cachegetUint8Memory0 === null ||
+    cachegetUint8Memory0.buffer !== wasm.memory.buffer
+  ) {
+    cachegetUint8Memory0 = new Uint8Array(wasm.memory.buffer)
+  }
+  return cachegetUint8Memory0
+}
+
+function getStringFromWasm0(ptr, len) {
+  return cachedTextDecoder.decode(getUint8Memory0().subarray(ptr, ptr + len))
+}
+
 let cachegetUint8ClampedMemory0 = null
 function getUint8ClampedMemory0() {
   if (
@@ -30,17 +54,6 @@ function addHeapObject(obj) {
   return idx
 }
 
-let cachegetUint8Memory0 = null
-function getUint8Memory0() {
-  if (
-    cachegetUint8Memory0 === null ||
-    cachegetUint8Memory0.buffer !== wasm.memory.buffer
-  ) {
-    cachegetUint8Memory0 = new Uint8Array(wasm.memory.buffer)
-  }
-  return cachegetUint8Memory0
-}
-
 let WASM_VECTOR_LEN = 0
 
 function passArray8ToWasm0(arg, malloc) {
@@ -161,7 +174,9 @@ async function init(input) {
     var ret = new ImageData(v0, arg2 >>> 0, arg3 >>> 0)
     return addHeapObject(ret)
   }
-
+  imports.wbg.__wbindgen_throw = function (arg0, arg1) {
+    throw new Error(getStringFromWasm0(arg0, arg1))
+  }
   if (
     typeof input === 'string' ||
     (typeof Request === 'function' && input instanceof Request) ||

test/integration/image-optimizer/test/index.test.js

@@ -482,6 +482,26 @@ function runTests({ w, isDev, domains }) {
     await expectWidth(res, 400)
   })
 
+  it('should not change the color type of a png', async () => {
+    // https://github.com/vercel/next.js/issues/22929
+    // A grayscaled PNG with transparent pixels.
+    const query = { url: '/grayscale.png', w: largeSize, q: 80 }
+    const opts = { headers: { accept: 'image/png' } }
+    const res = await fetchViaHTTP(appPort, '/_next/image', query, opts)
+    expect(res.status).toBe(200)
+    expect(res.headers.get('Content-Type')).toBe('image/png')
+    expect(res.headers.get('cache-control')).toBe(
+      'public, max-age=0, must-revalidate'
+    )
+
+    const png = await res.buffer()
+
+    // Read the color type byte (offset 9 + magic number 16).
+    // http://www.libpng.org/pub/png/spec/1.2/PNG-Chunks.html
+    const colorType = png.readUIntBE(25, 1)
+    expect(colorType).toBe(4)
+  })
+
   it("should error if the resource isn't a valid image", async () => {
     const query = { url: '/test.txt', w, q: 80 }
     const opts = { headers: { accept: 'image/webp' } }