Make blob: URLs cross‑realm and allow file‑backed Blob cloning

Detailed description:
- Add a global native blob URL registry so blob: URLs created in one realm are resolvable in another (e.g. main → worker). Registry entries store the DataQueue and metadata, are mutex‑protected, and are cleaned up via Environment cleanup hooks to avoid teardown races.
- Extend the DataQueue / Entry reader API to accept an optional `Environment*`, and update `FdEntry` reader creation so file handles and reader resources are created in the target environment/realm. This enables structured cloning / transferring of file‑backed Blobs across workers.
- Remove the JS-side prohibition on cloning file‑backed blobs so `structuredClone()` succeeds for file‑backed Blobs.
- Wire up Blob native bindings to use the new registry when storing/getting/revoking blob URLs; ensure Blob::GetDataObject constructs the Blob in the receiving environment.
- Add/update regression tests covering URL resolution in workers and cloning of file‑backed Blobs.

Files changed (high level):
- **node_blob.cc**: add global blob URL registry, Store/Get/Revoke helpers, env cleanup hook integration, Blob::StoreDataObject/GetDataObject/RevokeObjectURL wiring.
- **queue.h**, **queue.cc**: add optional `Environment*` parameter to `Entry::get_reader`, propagate env through DataQueue, implement `FdEntry::ReaderImpl::Create(entry, env)` to open file handles in the reader env.
- **blob.js**: remove `kNotCloneable` flag for file‑backed Blobs so they can be cloned/ transferred.
- **test-blob-url-worker.js**: new/updated regression test validating `resolveObjectURL` in a worker for a URL created on the main thread.
- **test-blob-file-backed.js**: update test to assert `structuredClone()` succeeds for file‑backed Blobs and that cloned content/metadata match.

Rationale and tests:
- These changes fix two related issues: blob URLs that only worked per‑realm, and file‑backed Blobs that were prevented from being cloned/transferred. Both were blocking cross‑realm Blob usage (main ↔ worker). All added/updated tests pass in the local test harness used during development.

Author: jimmywarting

lib/internal/blob.js

@@ -403,9 +403,7 @@ function createBlobFromFilePath(path, options) {
     return lazyDOMException('The blob could not be read', 'NotReadableError');
   }
   const { 0: blob, 1: length } = maybeBlob;
-  const res = createBlob(blob, length, options?.type);
-  res[kNotCloneable] = true;
-  return res;
+  return createBlob(blob, length, options?.type);
 }
 
 function arrayBuffer(blob) {

src/dataqueue/queue.cc

@@ -33,7 +33,7 @@ class NonIdempotentDataQueueReader;
 
 class EntryImpl : public DataQueue::Entry {
  public:
-  virtual std::shared_ptr<DataQueue::Reader> get_reader() = 0;
+  std::shared_ptr<DataQueue::Reader> get_reader(Environment* env = nullptr) override = 0;
 };
 
 class DataQueueImpl final : public DataQueue,
@@ -183,7 +183,7 @@ class DataQueueImpl final : public DataQueue,
     return !backpressure_listeners_.empty();
   }
 
-  std::shared_ptr<Reader> get_reader() override;
+  std::shared_ptr<Reader> get_reader(Environment* env = nullptr) override;
   SET_MEMORY_INFO_NAME(DataQueue)
   SET_SELF_SIZE(DataQueueImpl)
 
@@ -521,7 +521,7 @@ class NonIdempotentDataQueueReader final
   bool pull_pending_ = false;
 };
 
-std::shared_ptr<DataQueue::Reader> DataQueueImpl::get_reader() {
+std::shared_ptr<DataQueue::Reader> DataQueueImpl::get_reader(Environment* env) {
   if (is_idempotent()) {
     return std::make_shared<IdempotentDataQueueReader>(shared_from_this());
   }
@@ -573,7 +573,7 @@ class EmptyEntry final : public EntryImpl {
   EmptyEntry& operator=(const EmptyEntry&) = delete;
   EmptyEntry& operator=(EmptyEntry&&) = delete;
 
-  std::shared_ptr<DataQueue::Reader> get_reader() override {
+  std::shared_ptr<DataQueue::Reader> get_reader(Environment* env) override {
     return std::make_shared<EmptyReader>();
   }
 
@@ -661,7 +661,7 @@ class InMemoryEntry final : public EntryImpl {
   InMemoryEntry& operator=(const InMemoryEntry&) = delete;
   InMemoryEntry& operator=(InMemoryEntry&&) = delete;
 
-  std::shared_ptr<DataQueue::Reader> get_reader() override {
+  std::shared_ptr<DataQueue::Reader> get_reader(Environment* env) override {
     return std::make_shared<InMemoryReader>(*this);
   }
 
@@ -732,8 +732,8 @@ class DataQueueEntry : public EntryImpl {
   DataQueueEntry& operator=(const DataQueueEntry&) = delete;
   DataQueueEntry& operator=(DataQueueEntry&&) = delete;
 
-  std::shared_ptr<DataQueue::Reader> get_reader() override {
-    return std::make_shared<ReaderImpl>(data_queue_->get_reader());
+  std::shared_ptr<DataQueue::Reader> get_reader(Environment* env) override {
+    return std::make_shared<ReaderImpl>(data_queue_->get_reader(env));
   }
 
   std::unique_ptr<Entry> slice(
@@ -844,8 +844,8 @@ class FdEntry final : public EntryImpl {
     CHECK_LE(start, end);
   }
 
-  std::shared_ptr<DataQueue::Reader> get_reader() override {
-    return ReaderImpl::Create(this);
+  std::shared_ptr<DataQueue::Reader> get_reader(Environment* env) override {
+    return ReaderImpl::Create(this, env);
   }
 
   std::unique_ptr<Entry> slice(
@@ -901,7 +901,8 @@ class FdEntry final : public EntryImpl {
                            public StreamListener,
                            public std::enable_shared_from_this<ReaderImpl> {
    public:
-    static std::shared_ptr<ReaderImpl> Create(FdEntry* entry) {
+    static std::shared_ptr<ReaderImpl> Create(FdEntry* entry,
+                                                Environment* env) {
       uv_fs_t req;
       auto cleanup = OnScopeLeave([&] { uv_fs_req_cleanup(&req); });
       int file =
@@ -910,7 +911,8 @@ class FdEntry final : public EntryImpl {
         uv_fs_close(nullptr, &req, file, nullptr);
         return nullptr;
       }
-      Realm* realm = entry->env()->principal_realm();
+      Environment* reader_env = env ? env : entry->env();
+      Realm* realm = reader_env->principal_realm();
       return std::make_shared<ReaderImpl>(
           BaseObjectPtr<fs::FileHandle>(
               fs::FileHandle::New(realm->GetBindingData<fs::BindingData>(),

src/dataqueue/queue.h

@@ -186,6 +186,10 @@ class DataQueue : public MemoryRetainer {
     // idempotent and cannot preserve that quality, subsequent reads
     // must fail with an error when a variance is detected.
     virtual bool is_idempotent() const = 0;
+
+    // Create a reader for this entry. If `env` is provided, it may be used
+    // when the entry needs to create native resources in the current realm.
+    virtual std::shared_ptr<Reader> get_reader(Environment* env = nullptr) = 0;
   };
 
   // Creates an idempotent DataQueue with a pre-established collection
@@ -228,7 +232,7 @@ class DataQueue : public MemoryRetainer {
   // any number of readers can be created, all of which are guaranteed
   // to provide the same data. Otherwise, only a single reader is
   // permitted.
-  virtual std::shared_ptr<Reader> get_reader() = 0;
+  virtual std::shared_ptr<Reader> get_reader(Environment* env = nullptr) = 0;
 
   // Append a single new entry to the queue. Appending is only allowed
   // when is_idempotent() is false. std::nullopt will be returned

src/node_blob.cc

@@ -14,6 +14,10 @@
 #include "v8.h"
 
 #include <algorithm>
+#include <cstdlib>
+#include <mutex>
+#include <optional>
+#include <unordered_map>
 
 namespace node {
 
@@ -103,6 +107,48 @@ void Concat(const FunctionCallbackInfo<Value>& args) {
   args.GetReturnValue().Set(ArrayBuffer::New(isolate, std::move(store)));
 }
 
+struct BlobURLEntry {
+  std::shared_ptr<DataQueue> data_queue;
+  size_t length;
+  std::string type;
+};
+
+static std::mutex blob_url_registry_mutex;
+static std::unordered_map<std::string, BlobURLEntry> blob_url_registry;
+
+static void RevokeBlobURLEntry(const std::string& uuid);
+
+static void BlobURLCleanupHook(void* arg) {
+  std::string* uuid = static_cast<std::string*>(arg);
+  RevokeBlobURLEntry(*uuid);
+  delete uuid;
+}
+
+static void StoreBlobURLEntry(const std::string& uuid,
+                              std::shared_ptr<DataQueue> data_queue,
+                              size_t length,
+                              std::string type,
+                              Environment* env) {
+  std::lock_guard<std::mutex> lock(blob_url_registry_mutex);
+  blob_url_registry[uuid] = BlobURLEntry{std::move(data_queue), length,
+                                          std::move(type)};
+
+  std::string* uuid_copy = new std::string(uuid);
+  env->AddCleanupHook(BlobURLCleanupHook, uuid_copy);
+}
+
+static std::optional<BlobURLEntry> GetBlobURLEntry(const std::string& uuid) {
+  std::lock_guard<std::mutex> lock(blob_url_registry_mutex);
+  auto it = blob_url_registry.find(uuid);
+  if (it == blob_url_registry.end()) return std::nullopt;
+  return it->second;
+}
+
+static void RevokeBlobURLEntry(const std::string& uuid) {
+  std::lock_guard<std::mutex> lock(blob_url_registry_mutex);
+  blob_url_registry.erase(uuid);
+}
+
 void BlobFromFilePath(const FunctionCallbackInfo<Value>& args) {
   Environment* env = Environment::GetCurrent(args);
   BufferValue path(env->isolate(), args[0]);
@@ -302,7 +348,7 @@ Blob::Reader::Reader(Environment* env,
                      Local<Object> obj,
                      BaseObjectPtr<Blob> strong_ptr)
     : AsyncWrap(env, obj, AsyncWrap::PROVIDER_BLOBREADER),
-      inner_(strong_ptr->data_queue_->get_reader()),
+      inner_(strong_ptr->data_queue_->get_reader(env)),
       strong_ptr_(std::move(strong_ptr)) {
   MakeWeak();
 }
@@ -453,7 +499,6 @@ void Blob::StoreDataObject(const FunctionCallbackInfo<Value>& args) {
   CHECK(args[2]->IsUint32());  // Length
   CHECK(args[3]->IsString());  // Type
 
-  BlobBindingData* binding_data = realm->GetBindingData<BlobBindingData>();
   Isolate* isolate = realm->isolate();
 
   Utf8Value key(isolate, args[0]);
@@ -463,10 +508,8 @@ void Blob::StoreDataObject(const FunctionCallbackInfo<Value>& args) {
   size_t length = args[2].As<Uint32>()->Value();
   Utf8Value type(isolate, args[3]);
 
-  binding_data->store_data_object(
-      key.ToString(),
-      BlobBindingData::StoredDataObject(
-          BaseObjectPtr<Blob>(blob), length, type.ToString()));
+  StoreBlobURLEntry(key.ToString(), blob->data_queue_, length,
+                    type.ToString(), realm->env());
 }
 
 // Note: applying the V8 Fast API to the following function does not produce
@@ -475,7 +518,6 @@ void Blob::RevokeObjectURL(const FunctionCallbackInfo<Value>& args) {
   CHECK_GE(args.Length(), 1);
   CHECK(args[0]->IsString());
   Realm* realm = Realm::GetCurrent(args);
-  BlobBindingData* binding_data = realm->GetBindingData<BlobBindingData>();
   Isolate* isolate = realm->isolate();
 
   Utf8Value input(isolate, args[0].As<String>());
@@ -492,37 +534,38 @@ void Blob::RevokeObjectURL(const FunctionCallbackInfo<Value>& args) {
     auto end_index = pathname.find(':', start_index + 1);
     if (end_index == std::string_view::npos) {
       auto id = std::string(pathname.substr(start_index + 1));
-      binding_data->revoke_data_object(id);
+      RevokeBlobURLEntry(id);
     }
   }
 }
 
 void Blob::GetDataObject(const FunctionCallbackInfo<Value>& args) {
   CHECK(args[0]->IsString());
   Realm* realm = Realm::GetCurrent(args);
-  BlobBindingData* binding_data = realm->GetBindingData<BlobBindingData>();
   Isolate* isolate = realm->isolate();
 
   Utf8Value key(isolate, args[0]);
+  std::optional<BlobURLEntry> stored = GetBlobURLEntry(key.ToString());
+  if (!stored.has_value()) return;
+
+  Environment* env = realm->env();
+  BaseObjectPtr<Blob> blob = Blob::Create(env, stored->data_queue);
+  if (!blob) return;
+
+  Local<Value> type;
+  if (!String::NewFromUtf8(isolate,
+                           stored->type.c_str(),
+                           NewStringType::kNormal,
+                           static_cast<int>(stored->type.length()))
+           .ToLocal(&type)) {
+    return;
+  }
 
-  BlobBindingData::StoredDataObject stored =
-      binding_data->get_data_object(key.ToString());
-  if (stored.blob) {
-    Local<Value> type;
-    if (!String::NewFromUtf8(isolate,
-                             stored.type.c_str(),
-                             NewStringType::kNormal,
-                             static_cast<int>(stored.type.length()))
-             .ToLocal(&type)) {
-      return;
-    }
-
-    Local<Value> values[] = {stored.blob->object(),
-                             Uint32::NewFromUnsigned(isolate, stored.length),
-                             type};
+  Local<Value> values[] = {blob->object(),
+                           Uint32::NewFromUnsigned(isolate, stored->length),
+                           type};
 
-    args.GetReturnValue().Set(Array::New(isolate, values, arraysize(values)));
-  }
+  args.GetReturnValue().Set(Array::New(isolate, values, arraysize(values)));
 }
 
 void BlobBindingData::StoredDataObject::MemoryInfo(

test/parallel/test-blob-file-backed.js

@@ -130,12 +130,9 @@ writeFileSync(testfile5, '');
 })().then(common.mustCall());
 
 (async () => {
-  // We currently do not allow File-backed blobs to be cloned or transferred
-  // across worker threads. This is largely because the underlying FdEntry
-  // is bound to the Environment/Realm under which is was created.
   const blob = await openAsBlob(__filename);
-  assert.throws(() => structuredClone(blob), {
-    code: 'ERR_INVALID_STATE',
-    message: 'Invalid state: File-backed Blobs are not cloneable'
-  });
+  const clone = structuredClone(blob);
+  assert.strictEqual(clone.size, blob.size);
+  assert.strictEqual(clone.type, blob.type);
+  assert.strictEqual(await clone.text(), await blob.text());
 })().then(common.mustCall());

test/parallel/test-blob-url-worker.js

@@ -0,0 +1,30 @@
+'use strict';
+
+const common = require('../common');
+const assert = require('assert');
+const { isMainThread, parentPort, Worker } = require('worker_threads');
+const { Blob } = require('buffer');
+
+if (isMainThread) {
+  const blob = new Blob(['hello world']);
+  const url = URL.createObjectURL(blob);
+
+  const worker = new Worker(__filename);
+  worker.once('message', common.mustCall((value) => {
+    assert.deepStrictEqual(value, { size: 11, type: '', text: 'hello world' });
+    worker.terminate();
+  }));
+  worker.once('error', common.mustNotCall());
+  worker.once('exit', common.mustCall((code) => {
+    assert.strictEqual(code, 0);
+  }));
+
+  worker.postMessage(url);
+} else {
+  const { resolveObjectURL } = require('buffer');
+  parentPort.once('message', async (url) => {
+    const blob = resolveObjectURL(url);
+    const text = await blob.text();
+    parentPort.postMessage({ size: blob.size, type: blob.type, text });
+  });
+}