review comments

Author: Ethan-Arrowood

packages/next/src/server/stream-utils/node-web-streams-helper.ts

@@ -202,6 +202,7 @@ function createHeadInsertionTransformStream(
         controller.enqueue(chunk)
         freezing = true
       } else {
+        // TODO (@Ethan-Arrowood): Replace the generic `indexOfUint8Array` method with something finely tuned for the subset of things actually being checked for.
         const index = indexOfUint8Array(chunk, ENCODED_TAGS.CLOSED.HEAD)
         if (index !== -1) {
           const insertedHeadContent = new Uint8Array(
@@ -444,10 +445,22 @@ export function createRootLayoutValidatorStream(): TransformStream<
 > {
   let foundHtml = false
   let foundBody = false
-  let content = new Uint8Array(0)
+  let chunks: Uint8Array[] = []
+  let size = 0
   return new TransformStream({
     async transform(chunk, controller) {
-      content = concatUint8Arrays(content, chunk)
+      chunks.push(chunk)
+      size += chunk.length
+      controller.enqueue(chunk)
+    },
+    flush(controller) {
+      const content = new Uint8Array(size)
+      let offset = 0
+      for (const chunk of chunks) {
+        content.set(chunk, offset)
+        offset += chunk.length
+      }
+
       // Peek into the streamed chunk to see if the tags are present.
       if (!foundHtml || !foundBody) {
         if (
@@ -463,9 +476,7 @@ export function createRootLayoutValidatorStream(): TransformStream<
           foundBody = true
         }
       }
-      controller.enqueue(chunk)
-    },
-    flush(controller) {
+
       const missingTags: typeof window.__next_root_layout_missing_tags = []
       if (!foundHtml) missingTags.push('html')
       if (!foundBody) missingTags.push('body')

packages/next/src/server/stream-utils/uint8array-helpers.ts

@@ -2,7 +2,8 @@
  * Find the starting index of Uint8Array `b` within Uint8Array `a`.
  */
 export function indexOfUint8Array(a: Uint8Array, b: Uint8Array) {
-  if (a.length === 0 || b.length === 0 || b.length > a.length) return -1
+  if (b.length === 0) return 0
+  if (a.length === 0 || b.length > a.length) return -1
 
   // start iterating through `a`
   for (let i = 0; i <= a.length - b.length; i++) {
@@ -28,7 +29,13 @@ export function indexOfUint8Array(a: Uint8Array, b: Uint8Array) {
  * Check if two Uint8Arrays are strictly equivalent.
  */
 export function isEquivalentUint8Arrays(a: Uint8Array, b: Uint8Array) {
-  return a.length === b.length && a.every((v, i) => v === b[i])
+  if (a.length !== b.length) return false
+
+  for (let i = 0; i < a.length; i++) {
+    if (a[i] !== b[i]) return false
+  }
+
+  return true
 }
 
 /**
@@ -40,6 +47,7 @@ export function isEquivalentUint8Arrays(a: Uint8Array, b: Uint8Array) {
  */
 export function removeFromUint8Array(a: Uint8Array, b: Uint8Array) {
   const tagIndex = indexOfUint8Array(a, b)
+  if (tagIndex === 0) return a.subarray(b.length)
   if (tagIndex > -1) {
     const removed = new Uint8Array(a.length - b.length)
     removed.set(a.slice(0, tagIndex))