child_process: retain reference to data with advanced serialization

Do the same thing we do for other streams, and retain a reference to the Buffer that was sent over IPC while the write request is active, so that it doesn’t get garbage collected while the data is still in flight. (This is a good example of why it’s a bad idea that we’re not re-using the general streams implementation for IPC and instead maintain separate usage of the low-level I/O primitives.) Fixes: #34797
nodejs · addaleax · May 18, 2021 · May 18, 2021 · b91474c8e900de548690a01738a9488ae2b57381
commit b91474c8e900de548690a01738a9488ae2b57381
diff --git a/lib/internal/child_process/serialization.js b/lib/internal/child_process/serialization.js
@@ -12,6 +12,7 @@ const { StringDecoder } = require('string_decoder');
 const v8 = require('v8');
 const { isArrayBufferView } = require('internal/util/types');
 const assert = require('internal/assert');
+const { streamBaseState, kLastWriteWasAsync } = internalBinding('stream_wrap');
 
 const kMessageBuffer = Symbol('kMessageBuffer');
 const kJSONBuffer = Symbol('kJSONBuffer');
@@ -82,10 +83,16 @@ const advanced = {
     const serializedMessage = ser.releaseBuffer();
     const sizeBuffer = Buffer.allocUnsafe(4);
     sizeBuffer.writeUInt32BE(serializedMessage.length);
-    return channel.writeBuffer(req, Buffer.concat([
+
+    const buffer = Buffer.concat([
       sizeBuffer,
       serializedMessage,
-    ]), handle);
+    ]);
+    const result = channel.writeBuffer(req, buffer, handle);
+    // Mirror what stream_base_commons.js does for Buffer retention.
+    if (streamBaseState[kLastWriteWasAsync])
+      req.buffer = buffer;
+    return result;
   },
 };
 

diff --git a/test/parallel/test-child-process-advanced-serialization-largebuffer.js b/test/parallel/test-child-process-advanced-serialization-largebuffer.js
@@ -0,0 +1,27 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const child_process = require('child_process');
+
+// Regression test for https://github.com/nodejs/node/issues/34797
+const eightMB = 8 * 1024 * 1024;
+
+if (process.argv[2] === 'child') {
+  for (let i = 0; i < 4; i++) {
+    process.send(new Uint8Array(eightMB).fill(i));
+  }
+} else {
+  const child = child_process.spawn(process.execPath, [__filename, 'child'], {
+    stdio: ['inherit', 'inherit', 'inherit', 'ipc'],
+    serialization: 'advanced'
+  });
+  const received = [];
+  child.on('message', common.mustCall((chunk) => {
+    assert.deepStrictEqual(chunk, new Uint8Array(eightMB).fill(chunk[0]));
+
+    received.push(chunk[0]);
+    if (received.length === 4) {
+      assert.deepStrictEqual(received, [0, 1, 2, 3]);
+    }
+  }, 4));
+}