fix(ext/node): enable Buffer pool for strings (#29592)

Part 1 towards enabling `parallel/test-buffer-pool-untransferable.js`

ext/node/polyfills/_http_outgoing.ts

@@ -550,7 +550,7 @@ Object.defineProperties(
       if (data instanceof Buffer) {
         data = new Uint8Array(data.buffer, data.byteOffset, data.byteLength);
       }
-      if (data.buffer.byteLength > 0) {
+      if (data.byteLength > 0) {
         this._bodyWriter.ready.then(() => {
           if (this._bodyWriter.desiredSize > 0) {
             this._bodyWriter.write(data).then(() => {

ext/node/polyfills/internal/buffer.mjs

@@ -207,9 +207,8 @@ function createBuffer(length) {
       'The value "' + length + '" is invalid for option "size"',
     );
   }
-  const buf = new Uint8Array(length);
-  ObjectSetPrototypeOf(buf, BufferPrototype);
-  return buf;
+
+  return new FastBuffer(length);
 }
 
 /**
@@ -238,7 +237,24 @@ export function Buffer(arg, encodingOrOffset, length) {
   return _from(arg, encodingOrOffset, length);
 }
 
-Buffer.poolSize = 8192;
+Buffer.poolSize = 8 * 1024;
+let poolSize, poolOffset, allocPool, allocBuffer;
+
+function createPool() {
+  poolSize = Buffer.poolSize;
+  allocBuffer = new Uint8Array(poolSize);
+  allocPool = TypedArrayPrototypeGetBuffer(allocBuffer);
+  poolOffset = 0;
+}
+createPool();
+
+function alignPool() {
+  // Ensure aligned slices
+  if (poolOffset & 0x7) {
+    poolOffset |= 0x7;
+    poolOffset++;
+  }
+}
 
 function _from(value, encodingOrOffset, length) {
   if (typeof value === "string") {
@@ -396,7 +412,9 @@ function fromString(string, encoding) {
   if (!BufferIsEncoding(encoding)) {
     throw new codes.ERR_UNKNOWN_ENCODING(encoding);
   }
+  const maxLength = Buffer.poolSize >>> 1;
   const length = byteLength(string, encoding) | 0;
+  if (length >= maxLength) {
     let buf = createBuffer(length);
     const actual = buf.write(string, encoding);
     if (actual !== length) {
@@ -404,12 +422,26 @@ function fromString(string, encoding) {
       buf = buf.slice(0, actual);
     }
     return buf;
+  }
+
+  if (length > (poolSize - poolOffset)) {
+    createPool();
+  }
+  const ops = getEncodingOps(encoding);
+  let b = new FastBuffer(allocPool, poolOffset, length);
+  const actual = ops.write(b, string, 0, length);
+  if (actual !== length) {
+    // byteLength() may overestimate the length, so we slice it down.
+    b = new FastBuffer(allocPool, poolOffset, actual);
+  }
+
+  poolOffset += actual;
+  alignPool();
+  return b;
 }
 
 function fromArrayLike(obj) {
-  const buf = new Uint8Array(obj);
-  ObjectSetPrototypeOf(buf, BufferPrototype);
-  return buf;
+  return new FastBuffer(obj);
 }
 
 function fromObject(obj) {
@@ -447,7 +479,7 @@ ObjectSetPrototypeOf(SlowBuffer.prototype, Uint8ArrayPrototype);
 ObjectSetPrototypeOf(SlowBuffer, Uint8Array);
 
 const BufferIsBuffer = Buffer.isBuffer = function isBuffer(b) {
-  return b != null && b._isBuffer === true && b !== BufferPrototype;
+  return ObjectPrototypeIsPrototypeOf(Buffer.prototype, b);
 };
 
 const BufferCompare = Buffer.compare = function compare(a, b) {
@@ -1072,9 +1104,7 @@ function fromArrayBuffer(obj, byteOffset, length) {
     }
   }
 
-  const buffer = new Uint8Array(obj, byteOffset, length);
-  ObjectSetPrototypeOf(buffer, BufferPrototype);
-  return buffer;
+  return new FastBuffer(obj, byteOffset, length);
 }
 
 function _base64Slice(buf, start, end) {

ext/node/polyfills/string_decoder.ts

@@ -39,10 +39,15 @@ const {
   Symbol,
   MathMin,
   DataViewPrototypeGetBuffer,
+  DataViewPrototypeGetByteLength,
+  DataViewPrototypeGetByteOffset,
   ObjectPrototypeIsPrototypeOf,
   String,
   TypedArrayPrototypeGetBuffer,
+  TypedArrayPrototypeGetByteLength,
+  TypedArrayPrototypeGetByteOffset,
   StringPrototypeToLowerCase,
+  Uint8Array,
 } = primordials;
 const { isTypedArray } = core;
 
@@ -84,10 +89,19 @@ function normalizeBuffer(buf: Buffer) {
   if (isBufferType(buf)) {
     return buf;
   } else {
+    const isTA = isTypedArray(buf);
     return Buffer.from(
-      isTypedArray(buf)
+      new Uint8Array(
+        isTA
           ? TypedArrayPrototypeGetBuffer(buf)
           : DataViewPrototypeGetBuffer(buf),
+        isTA
+          ? TypedArrayPrototypeGetByteOffset(buf)
+          : DataViewPrototypeGetByteOffset(buf),
+        isTA
+          ? TypedArrayPrototypeGetByteLength(buf)
+          : DataViewPrototypeGetByteLength(buf),
+      ),
     );
   }
 }

tests/unit_node/buffer_test.ts

@@ -1,6 +1,7 @@
 // Copyright 2018-2025 the Deno authors. MIT license.
 import { Buffer } from "node:buffer";
 import { assertEquals, assertThrows } from "@std/assert";
+import { strictEqual } from "node:assert";
 
 Deno.test({
   name: "[node/buffer] alloc fails if size is not a number",
@@ -651,3 +652,12 @@ Deno.test({
     assertEquals([...buf], [0x61, 0x62, 0x63, 0, 0, 0, 0, 0]);
   },
 });
+
+Deno.test({
+  name: "[node/buffer] Buffer.from pool",
+  fn() {
+    const a = Buffer.from("hello world");
+    const b = Buffer.from("hello world");
+    strictEqual(a.buffer, b.buffer);
+  },
+});

tests/unit_node/child_process_test.ts

@@ -1153,8 +1153,9 @@ Deno.test({
       assertEquals(stdout.toString(), expected);
     }
     {
+      const b = Buffer.from(text);
       const { stdout } = spawnSync(Deno.execPath(), ["fmt", "-"], {
-        input: new DataView(Buffer.from(text).buffer),
+        input: new DataView(b.buffer, b.byteOffset, b.byteLength),
       });
       assertEquals(stdout.toString(), expected);
     }

tests/unit_node/zlib_test.ts

@@ -133,7 +133,9 @@ Deno.test(
 
 Deno.test("should work with dataview", () => {
   const buf = Buffer.from("hello world");
-  const compressed = brotliCompressSync(new DataView(buf.buffer));
+  const compressed = brotliCompressSync(
+    new DataView(buf.buffer, buf.byteOffset, buf.byteLength),
+  );
   const decompressed = brotliDecompressSync(compressed);
   assertEquals(decompressed.toString(), "hello world");
 });
@@ -164,7 +166,9 @@ Deno.test(
   "zlib compression with dataview",
   () => {
     const buf = Buffer.from("hello world");
-    const compressed = gzipSync(new DataView(buf.buffer));
+    const compressed = gzipSync(
+      new DataView(buf.buffer, buf.byteOffset, buf.byteLength),
+    );
     const decompressed = unzipSync(compressed);
     assertEquals(decompressed.toString(), "hello world");
   },