worker,fs: make FileHandle transferable

Allow passing `FileHandle` instances in the transfer list of a `.postMessage()` call. PR-URL: #33772 Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
nodejs · addaleax · Apr 8, 2020 · Apr 9, 2020 · Jun 6, 2020 · Jun 6, 2020
commit 9e99e136d200ff7167605bea472f09b051d472f7
diff --git a/doc/api/worker_threads.md b/doc/api/worker_threads.md
@@ -318,6 +318,10 @@ are part of the channel.
 ### `port.postMessage(value[, transferList])`
 <!-- YAML
 added: v10.5.0
+changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/33772
+    description: Added `FileHandle` to the list of transferable types.
 -->
 
 * `value` {any}
@@ -335,7 +339,8 @@ In particular, the significant differences to `JSON` are:
 * `value` may contain typed arrays, both using `ArrayBuffer`s
    and `SharedArrayBuffer`s.
 * `value` may contain [`WebAssembly.Module`][] instances.
-* `value` may not contain native (C++-backed) objects other than `MessagePort`s.
+* `value` may not contain native (C++-backed) objects other than `MessagePort`s
+  and [`FileHandle`][]s.
 
 ```js
 const { MessageChannel } = require('worker_threads');
@@ -349,7 +354,8 @@ circularData.foo = circularData;
 port2.postMessage(circularData);
 ```
 
-`transferList` may be a list of `ArrayBuffer` and `MessagePort` objects.
+`transferList` may be a list of [`ArrayBuffer`][], [`MessagePort`][] and
+[`FileHandle`][] objects.
 After transferring, they will not be usable on the sending side of the channel
 anymore (even if they are not contained in `value`). Unlike with
 [child processes][], transferring handles such as network sockets is currently
@@ -810,13 +816,15 @@ active handle in the event system. If the worker is already `unref()`ed calling
 
 [`'close'` event]: #worker_threads_event_close
 [`'exit'` event]: #worker_threads_event_exit
+[`ArrayBuffer`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer
 [`AsyncResource`]: async_hooks.html#async_hooks_class_asyncresource
 [`Buffer`]: buffer.html
 [`Buffer.allocUnsafe()`]: buffer.html#buffer_class_method_buffer_allocunsafe_size
 [`ERR_MISSING_MESSAGE_PORT_IN_TRANSFER_LIST`]: errors.html#errors_err_missing_message_port_in_transfer_list
 [`ERR_WORKER_NOT_RUNNING`]: errors.html#ERR_WORKER_NOT_RUNNING
 [`EventEmitter`]: events.html
 [`EventTarget`]: https://developer.mozilla.org/en-US/docs/Web/API/EventTarget
+[`FileHandle`]: fs.html#fs_class_filehandle
 [`MessagePort`]: #worker_threads_class_messageport
 [`SharedArrayBuffer`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer
 [`Uint8Array`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array

diff --git a/lib/internal/fs/promises.js b/lib/internal/fs/promises.js
@@ -65,13 +65,17 @@ const { promisify } = require('internal/util');
 const kHandle = Symbol('kHandle');
 const kFd = Symbol('kFd');
 const { kUsePromises } = binding;
+const {
+  JSTransferable, kDeserialize, kTransfer, kTransferList
+} = require('internal/worker/js_transferable');
 
 const getDirectoryEntriesPromise = promisify(getDirents);
 
-class FileHandle {
+class FileHandle extends JSTransferable {
   constructor(filehandle) {
+    super();
     this[kHandle] = filehandle;
-    this[kFd] = filehandle.fd;
+    this[kFd] = filehandle ? filehandle.fd : -1;
   }
 
   getAsyncId() {
@@ -142,6 +146,26 @@ class FileHandle {
     this[kFd] = -1;
     return this[kHandle].close();
   }
+
+  [kTransfer]() {
+    const handle = this[kHandle];
+    this[kFd] = -1;
+    this[kHandle] = null;
+
+    return {
+      data: { handle },
+      deserializeInfo: 'internal/fs/promises:FileHandle'
+    };
+  }
+
+  [kTransferList]() {
+    return [ this[kHandle] ];
+  }
+
+  [kDeserialize]({ handle }) {
+    this[kHandle] = handle;
+    this[kFd] = handle.fd;
+  }
 }
 
 function validateFileHandle(handle) {

diff --git a/lib/internal/worker/js_transferable.js b/lib/internal/worker/js_transferable.js
@@ -1,4 +1,5 @@
 'use strict';
+const { Error } = primordials;
 const {
   messaging_deserialize_symbol,
   messaging_transfer_symbol,
@@ -17,6 +18,13 @@ function setup() {
   setDeserializerCreateObjectFunction((deserializeInfo) => {
     const [ module, ctor ] = deserializeInfo.split(':');
     const Ctor = require(module)[ctor];
+    if (typeof Ctor !== 'function' ||
+        !(Ctor.prototype instanceof JSTransferable)) {
+      // Not one of the official errors because one should not be able to get
+      // here without messing with Node.js internals.
+      // eslint-disable-next-line no-restricted-syntax
+      throw new Error(`Unknown deserialize spec ${deserializeInfo}`);
+    }
     return new Ctor();
   });
 }

diff --git a/src/node_file.cc b/src/node_file.cc
@@ -190,6 +190,40 @@ void FileHandle::MemoryInfo(MemoryTracker* tracker) const {
   tracker->TrackField("current_read", current_read_);
 }
 
+FileHandle::TransferMode FileHandle::GetTransferMode() const {
+  return reading_ || closing_ || closed_ ?
+      TransferMode::kUntransferable : TransferMode::kTransferable;
+}
+
+std::unique_ptr<worker::TransferData> FileHandle::TransferForMessaging() {
+  CHECK_NE(GetTransferMode(), TransferMode::kUntransferable);
+  auto ret = std::make_unique<TransferData>(fd_);
+  closed_ = true;
+  return ret;
+}
+
+FileHandle::TransferData::TransferData(int fd) : fd_(fd) {}
+
+FileHandle::TransferData::~TransferData() {
+  if (fd_ > 0) {
+    uv_fs_t close_req;
+    CHECK_EQ(0, uv_fs_close(nullptr, &close_req, fd_, nullptr));
+    uv_fs_req_cleanup(&close_req);
+  }
+}
+
+BaseObjectPtr<BaseObject> FileHandle::TransferData::Deserialize(
+    Environment* env,
+    v8::Local<v8::Context> context,
+    std::unique_ptr<worker::TransferData> self) {
+  BindingData* bd = Environment::GetBindingData<BindingData>(context);
+  if (bd == nullptr) return {};
+
+  int fd = fd_;
+  fd_ = -1;
+  return BaseObjectPtr<BaseObject> { FileHandle::New(bd, fd) };
+}
+
 // Close the file descriptor if it hasn't already been closed. A process
 // warning will be emitted using a SetImmediate to avoid calling back to
 // JS during GC. If closing the fd fails at this point, a fatal exception

diff --git a/src/node_file.h b/src/node_file.h
@@ -5,6 +5,7 @@
 
 #include "node.h"
 #include "aliased_buffer.h"
+#include "node_messaging.h"
 #include "stream_base.h"
 #include <iostream>
 
@@ -273,7 +274,28 @@ class FileHandle final : public AsyncWrap, public StreamBase {
   FileHandle(const FileHandle&&) = delete;
   FileHandle& operator=(const FileHandle&&) = delete;
 
+  TransferMode GetTransferMode() const override;
+  std::unique_ptr<worker::TransferData> TransferForMessaging() override;
+
  private:
+  class TransferData : public worker::TransferData {
+   public:
+    explicit TransferData(int fd);
+    ~TransferData();
+
+    BaseObjectPtr<BaseObject> Deserialize(
+        Environment* env,
+        v8::Local<v8::Context> context,
+        std::unique_ptr<worker::TransferData> self) override;
+
+    SET_NO_MEMORY_INFO()
+    SET_MEMORY_INFO_NAME(FileHandleTransferData)
+    SET_SELF_SIZE(TransferData)
+
+   private:
+    int fd_;
+  };
+
   FileHandle(BindingData* binding_data, v8::Local<v8::Object> obj, int fd);
 
   // Synchronous close that emits a warning

diff --git a/test/parallel/test-worker-message-port-transfer-fake-js-transferable-internal.js b/test/parallel/test-worker-message-port-transfer-fake-js-transferable-internal.js
@@ -0,0 +1,33 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const fs = require('fs').promises;
+const { MessageChannel } = require('worker_threads');
+const { once } = require('events');
+
+// Test that overriding the internal kTransfer method of a JSTransferable does
+// not enable loading arbitrary code from internal Node.js core modules.
+
+(async function() {
+  const fh = await fs.open(__filename);
+  assert.strictEqual(fh.constructor.name, 'FileHandle');
+
+  const kTransfer = Object.getOwnPropertySymbols(Object.getPrototypeOf(fh))
+    .filter((symbol) => symbol.description === 'messaging_transfer_symbol')[0];
+  assert.strictEqual(typeof kTransfer, 'symbol');
+  fh[kTransfer] = () => {
+    return {
+      data: '✨',
+      deserializeInfo: 'net:Socket'
+    };
+  };
+
+  const { port1, port2 } = new MessageChannel();
+  port1.postMessage(fh, [ fh ]);
+  port2.on('message', common.mustNotCall());
+
+  const [ exception ] = await once(process, 'uncaughtException');
+
+  assert.strictEqual(exception.message, 'Unknown deserialize spec net:Socket');
+  port2.close();
+})().then(common.mustCall());
diff --git a/test/parallel/test-worker-message-port-transfer-fake-js-transferable.js b/test/parallel/test-worker-message-port-transfer-fake-js-transferable.js
@@ -0,0 +1,37 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const fs = require('fs').promises;
+const { MessageChannel } = require('worker_threads');
+const { once } = require('events');
+
+// Test that overriding the internal kTransfer method of a JSTransferable does
+// not enable loading arbitrary code from the disk.
+
+module.exports = {
+  NotARealClass: common.mustNotCall()
+};
+
+(async function() {
+  const fh = await fs.open(__filename);
+  assert.strictEqual(fh.constructor.name, 'FileHandle');
+
+  const kTransfer = Object.getOwnPropertySymbols(Object.getPrototypeOf(fh))
+    .filter((symbol) => symbol.description === 'messaging_transfer_symbol')[0];
+  assert.strictEqual(typeof kTransfer, 'symbol');
+  fh[kTransfer] = () => {
+    return {
+      data: '✨',
+      deserializeInfo: `${__filename}:NotARealClass`
+    };
+  };
+
+  const { port1, port2 } = new MessageChannel();
+  port1.postMessage(fh, [ fh ]);
+  port2.on('message', common.mustNotCall());
+
+  const [ exception ] = await once(process, 'uncaughtException');
+
+  assert.match(exception.message, /Missing internal module/);
+  port2.close();
+})().then(common.mustCall());
diff --git a/test/parallel/test-worker-message-port-transfer-filehandle.js b/test/parallel/test-worker-message-port-transfer-filehandle.js
@@ -0,0 +1,65 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const fs = require('fs').promises;
+const vm = require('vm');
+const { MessageChannel, moveMessagePortToContext } = require('worker_threads');
+const { once } = require('events');
+
+(async function() {
+  const fh = await fs.open(__filename);
+
+  const { port1, port2 } = new MessageChannel();
+
+  assert.throws(() => {
+    port1.postMessage(fh);
+  }, {
+    // See the TODO about error code in node_messaging.cc.
+    code: 'ERR_MISSING_MESSAGE_PORT_IN_TRANSFER_LIST'
+  });
+
+  // Check that transferring FileHandle instances works.
+  assert.notStrictEqual(fh.fd, -1);
+  port1.postMessage(fh, [ fh ]);
+  assert.strictEqual(fh.fd, -1);
+
+  const [ fh2 ] = await once(port2, 'message');
+  assert.strictEqual(Object.getPrototypeOf(fh2), Object.getPrototypeOf(fh));
+
+  assert.deepStrictEqual(await fh2.readFile(), await fs.readFile(__filename));
+  await fh2.close();
+
+  assert.rejects(() => fh.readFile(), { code: 'EBADF' });
+})().then(common.mustCall());
+
+(async function() {
+  // Check that there is no crash if the message is never read.
+  const fh = await fs.open(__filename);
+
+  const { port1 } = new MessageChannel();
+
+  assert.notStrictEqual(fh.fd, -1);
+  port1.postMessage(fh, [ fh ]);
+  assert.strictEqual(fh.fd, -1);
+})().then(common.mustCall());
+
+(async function() {
+  // Check that in the case of a context mismatch the message is discarded.
+  const fh = await fs.open(__filename);
+
+  const { port1, port2 } = new MessageChannel();
+
+  const ctx = vm.createContext();
+  const port2moved = moveMessagePortToContext(port2, ctx);
+  port2moved.onmessage = common.mustCall((msgEvent) => {
+    assert.strictEqual(msgEvent.data, 'second message');
+    port1.close();
+  });
+  port2moved.start();
+
+  assert.notStrictEqual(fh.fd, -1);
+  port1.postMessage(fh, [ fh ]);
+  assert.strictEqual(fh.fd, -1);
+
+  port1.postMessage('second message');
+})().then(common.mustCall());