buffer: recreate pool after transfer

Fixes: #61362

Author: lindsaycode05

lib/buffer.js

@@ -160,6 +160,12 @@ function createPool() {
 }
 createPool();
 
+function ensurePool() {
+  // Recreate the pool if it was detached (e.g., via ArrayBuffer.prototype.transfer).
+  if (allocPool.byteLength === 0)
+    createPool();
+}
+
 function alignPool() {
   // Ensure aligned slices
   if (poolOffset & 0x7) {
@@ -436,6 +442,7 @@ function allocate(size) {
     return new FastBuffer();
   }
   if (size < (Buffer.poolSize >>> 1)) {
+    ensurePool();
     if (size > (poolSize - poolOffset))
       createPool();
     const b = new FastBuffer(allocPool, poolOffset, size);
@@ -462,6 +469,7 @@ function fromStringFast(string, ops) {
   if (length >= maxLength)
     return createFromString(string, ops, length);
 
+  ensurePool();
   if (length > (poolSize - poolOffset))
     createPool();
 
@@ -525,6 +533,7 @@ function fromArrayLike(obj) {
   if (obj.length <= 0)
     return new FastBuffer();
   if (obj.length < (Buffer.poolSize >>> 1)) {
+    ensurePool();
     if (obj.length > (poolSize - poolOffset))
       createPool();
     const b = new FastBuffer(allocPool, poolOffset, obj.length);

test/parallel/test-buffer-pool-untransferable.js

@@ -21,3 +21,16 @@ assert.throws(() => port1.postMessage(a, [ a.buffer ]), {
 // Verify that the pool ArrayBuffer has not actually been transferred:
 assert.strictEqual(a.buffer, b.buffer);
 assert.strictEqual(a.length, length);
+
+if (typeof ArrayBuffer.prototype.transfer !== 'function')
+  common.skip('ArrayBuffer.prototype.transfer is not available');
+
+// Regression test for https://github.com/nodejs/node/issues/61362
+const base64 = 'aGVsbG8='; // "hello"
+const buf = Buffer.from(base64, 'base64');
+buf.buffer.transfer();
+assert.strictEqual(buf.buffer.byteLength, 0);
+assert.doesNotThrow(() => {
+  const out = Buffer.from(base64, 'base64');
+  assert.strictEqual(out.toString(), 'hello');
+});