1 files changed, 667 insertions, 0 deletions
diff --git a/dom/file/MutableBlobStorage.cpp b/dom/file/MutableBlobStorage.cpp
new file mode 100644
index 0000000000..3bb1a4f169
--- /dev/null
+++ b/dom/file/MutableBlobStorage.cpp
@@ -0,0 +1,667 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "EmptyBlobImpl.h"
+#include "MutableBlobStorage.h"
+#include "MemoryBlobImpl.h"
+#include "mozilla/CheckedInt.h"
+#include "mozilla/dom/TemporaryIPCBlobChild.h"
+#include "mozilla/dom/WorkerPrivate.h"
+#include "mozilla/ipc/BackgroundChild.h"
+#include "mozilla/ipc/PBackgroundChild.h"
+#include "mozilla/Preferences.h"
+#include "mozilla/TaskQueue.h"
+#include "File.h"
+#include "nsAnonymousTemporaryFile.h"
+#include "nsNetCID.h"
+#include "nsProxyRelease.h"
+
+#define BLOB_MEMORY_TEMPORARY_FILE 1048576
+
+namespace mozilla::dom {
+
+namespace {
+
+// This class uses the callback to inform when the Blob is created or when the
+// error must be propagated.
+class BlobCreationDoneRunnable final : public Runnable {
+ public:
+  BlobCreationDoneRunnable(MutableBlobStorage* aBlobStorage,
+                           MutableBlobStorageCallback* aCallback,
+                           BlobImpl* aBlobImpl, nsresult aRv)
+      : Runnable("dom::BlobCreationDoneRunnable"),
+        mBlobStorage(aBlobStorage),
+        mCallback(aCallback),
+        mBlobImpl(aBlobImpl),
+        mRv(aRv) {
+    MOZ_ASSERT(aBlobStorage);
+    MOZ_ASSERT(aCallback);
+    MOZ_ASSERT((NS_FAILED(aRv) && !aBlobImpl) ||
+               (NS_SUCCEEDED(aRv) && aBlobImpl));
+  }
+
+  NS_IMETHOD
+  Run() override {
+    MOZ_ASSERT(NS_IsMainThread());
+    MOZ_ASSERT(mBlobStorage);
+    mCallback->BlobStoreCompleted(mBlobStorage, mBlobImpl, mRv);
+    mCallback = nullptr;
+    mBlobImpl = nullptr;
+    return NS_OK;
+  }
+
+ private:
+  ~BlobCreationDoneRunnable() override {
+    MOZ_ASSERT(mBlobStorage);
+    // If something when wrong, we still have to release these objects in the
+    // correct thread.
+    NS_ProxyRelease("BlobCreationDoneRunnable::mCallback",
+                    mBlobStorage->EventTarget(), mCallback.forget());
+  }
+
+  RefPtr<MutableBlobStorage> mBlobStorage;
+  RefPtr<MutableBlobStorageCallback> mCallback;
+  RefPtr<BlobImpl> mBlobImpl;
+  nsresult mRv;
+};
+
+// Simple runnable to propagate the error to the BlobStorage.
+class ErrorPropagationRunnable final : public Runnable {
+ public:
+  ErrorPropagationRunnable(MutableBlobStorage* aBlobStorage, nsresult aRv)
+      : Runnable("dom::ErrorPropagationRunnable"),
+        mBlobStorage(aBlobStorage),
+        mRv(aRv) {}
+
+  NS_IMETHOD
+  Run() override {
+    mBlobStorage->ErrorPropagated(mRv);
+    return NS_OK;
+  }
+
+ private:
+  RefPtr<MutableBlobStorage> mBlobStorage;
+  nsresult mRv;
+};
+
+// This runnable moves a buffer to the IO thread and there, it writes it into
+// the temporary file, if its File Descriptor has not been already closed.
+class WriteRunnable final : public Runnable {
+ public:
+  static WriteRunnable* CopyBuffer(MutableBlobStorage* aBlobStorage,
+                                   const void* aData, uint32_t aLength) {
+    MOZ_ASSERT(aBlobStorage);
+    MOZ_ASSERT(aData);
+
+    // We have to take a copy of this buffer.
+    void* data = malloc(aLength);
+    if (!data) {
+      return nullptr;
+    }
+
+    memcpy((char*)data, aData, aLength);
+    return new WriteRunnable(aBlobStorage, data, aLength);
+  }
+
+  static WriteRunnable* AdoptBuffer(MutableBlobStorage* aBlobStorage,
+                                    void* aData, uint32_t aLength) {
+    MOZ_ASSERT(NS_IsMainThread());
+    MOZ_ASSERT(aBlobStorage);
+    MOZ_ASSERT(aData);
+
+    return new WriteRunnable(aBlobStorage, aData, aLength);
+  }
+
+  NS_IMETHOD
+  Run() override {
+    MOZ_ASSERT(!NS_IsMainThread());
+    MOZ_ASSERT(mBlobStorage);
+
+    PRFileDesc* fd = mBlobStorage->GetFD();
+    if (!fd) {
+      // The file descriptor has been closed in the meantime.
+      return NS_OK;
+    }
+
+    int32_t written = PR_Write(fd, mData, mLength);
+    if (NS_WARN_IF(written < 0 || uint32_t(written) != mLength)) {
+      mBlobStorage->CloseFD();
+      return mBlobStorage->EventTarget()->Dispatch(
+          new ErrorPropagationRunnable(mBlobStorage, NS_ERROR_FAILURE),
+          NS_DISPATCH_NORMAL);
+    }
+
+    return NS_OK;
+  }
+
+ private:
+  WriteRunnable(MutableBlobStorage* aBlobStorage, void* aData, uint32_t aLength)
+      : Runnable("dom::WriteRunnable"),
+        mBlobStorage(aBlobStorage),
+        mData(aData),
+        mLength(aLength) {
+    MOZ_ASSERT(mBlobStorage);
+    MOZ_ASSERT(aData);
+  }
+
+  ~WriteRunnable() override { free(mData); }
+
+  RefPtr<MutableBlobStorage> mBlobStorage;
+  void* mData;
+  uint32_t mLength;
+};
+
+// This runnable closes the FD in case something goes wrong or the temporary
+// file is not needed anymore.
+class CloseFileRunnable final : public Runnable {
+ public:
+  explicit CloseFileRunnable(PRFileDesc* aFD)
+      : Runnable("dom::CloseFileRunnable"), mFD(aFD) {}
+
+  NS_IMETHOD
+  Run() override {
+    MOZ_ASSERT(!NS_IsMainThread());
+    PR_Close(mFD);
+    mFD = nullptr;
+    return NS_OK;
+  }
+
+ private:
+  ~CloseFileRunnable() override {
+    if (mFD) {
+      PR_Close(mFD);
+    }
+  }
+
+  PRFileDesc* mFD;
+};
+
+// This runnable is dispatched to the main-thread from the IO thread and its
+// task is to create the blob and inform the callback.
+class CreateBlobRunnable final : public Runnable,
+                                 public TemporaryIPCBlobChildCallback {
+ public:
+  // We need to always declare refcounting because
+  // TemporaryIPCBlobChildCallback has pure-virtual refcounting.
+  NS_DECL_ISUPPORTS_INHERITED
+
+  CreateBlobRunnable(MutableBlobStorage* aBlobStorage,
+                     const nsACString& aContentType,
+                     already_AddRefed<MutableBlobStorageCallback> aCallback)
+      : Runnable("dom::CreateBlobRunnable"),
+        mBlobStorage(aBlobStorage),
+        mContentType(aContentType),
+        mCallback(aCallback) {
+    MOZ_ASSERT(!NS_IsMainThread());
+    MOZ_ASSERT(aBlobStorage);
+  }
+
+  NS_IMETHOD
+  Run() override {
+    MOZ_ASSERT(NS_IsMainThread());
+    MOZ_ASSERT(mBlobStorage);
+    mBlobStorage->AskForBlob(this, mContentType);
+    return NS_OK;
+  }
+
+  void OperationSucceeded(BlobImpl* aBlobImpl) override {
+    RefPtr<MutableBlobStorageCallback> callback(std::move(mCallback));
+    callback->BlobStoreCompleted(mBlobStorage, aBlobImpl, NS_OK);
+  }
+
+  void OperationFailed(nsresult aRv) override {
+    RefPtr<MutableBlobStorageCallback> callback(std::move(mCallback));
+    callback->BlobStoreCompleted(mBlobStorage, nullptr, aRv);
+  }
+
+ private:
+  ~CreateBlobRunnable() override {
+    MOZ_ASSERT(mBlobStorage);
+    // If something when wrong, we still have to release data in the correct
+    // thread.
+    NS_ProxyRelease("CreateBlobRunnable::mCallback",
+                    mBlobStorage->EventTarget(), mCallback.forget());
+  }
+
+  RefPtr<MutableBlobStorage> mBlobStorage;
+  nsCString mContentType;
+  RefPtr<MutableBlobStorageCallback> mCallback;
+};
+
+NS_IMPL_ISUPPORTS_INHERITED0(CreateBlobRunnable, Runnable)
+
+// This task is used to know when the writing is completed. From the IO thread
+// it dispatches a CreateBlobRunnable to the main-thread.
+class LastRunnable final : public Runnable {
+ public:
+  LastRunnable(MutableBlobStorage* aBlobStorage, const nsACString& aContentType,
+               MutableBlobStorageCallback* aCallback)
+      : Runnable("dom::LastRunnable"),
+        mBlobStorage(aBlobStorage),
+        mContentType(aContentType),
+        mCallback(aCallback) {
+    MOZ_ASSERT(NS_IsMainThread());
+    MOZ_ASSERT(mBlobStorage);
+    MOZ_ASSERT(aCallback);
+  }
+
+  NS_IMETHOD
+  Run() override {
+    MOZ_ASSERT(!NS_IsMainThread());
+
+    RefPtr<Runnable> runnable =
+        new CreateBlobRunnable(mBlobStorage, mContentType, mCallback.forget());
+    return mBlobStorage->EventTarget()->Dispatch(runnable, NS_DISPATCH_NORMAL);
+  }
+
+ private:
+  ~LastRunnable() override {
+    MOZ_ASSERT(mBlobStorage);
+    // If something when wrong, we still have to release data in the correct
+    // thread.
+    NS_ProxyRelease("LastRunnable::mCallback", mBlobStorage->EventTarget(),
+                    mCallback.forget());
+  }
+
+  RefPtr<MutableBlobStorage> mBlobStorage;
+  nsCString mContentType;
+  RefPtr<MutableBlobStorageCallback> mCallback;
+};
+
+}  // anonymous namespace
+
+MutableBlobStorage::MutableBlobStorage(MutableBlobStorageType aType,
+                                       nsIEventTarget* aEventTarget,
+                                       uint32_t aMaxMemory)
+    : mMutex("MutableBlobStorage::mMutex"),
+      mData(nullptr),
+      mDataLen(0),
+      mDataBufferLen(0),
+      mStorageState(aType == eOnlyInMemory ? eKeepInMemory : eInMemory),
+      mFD(nullptr),
+      mErrorResult(NS_OK),
+      mEventTarget(aEventTarget),
+      mMaxMemory(aMaxMemory) {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  if (!mEventTarget) {
+    mEventTarget = GetMainThreadEventTarget();
+  }
+
+  if (aMaxMemory == 0 && aType == eCouldBeInTemporaryFile) {
+    mMaxMemory = Preferences::GetUint("dom.blob.memoryToTemporaryFile",
+                                      BLOB_MEMORY_TEMPORARY_FILE);
+  }
+
+  MOZ_ASSERT(mEventTarget);
+}
+
+MutableBlobStorage::~MutableBlobStorage() {
+  free(mData);
+
+  if (mFD) {
+    RefPtr<Runnable> runnable = new CloseFileRunnable(mFD);
+    Unused << DispatchToIOThread(runnable.forget());
+  }
+
+  if (mTaskQueue) {
+    mTaskQueue->BeginShutdown();
+  }
+
+  if (mActor) {
+    NS_ProxyRelease("MutableBlobStorage::mActor", EventTarget(),
+                    mActor.forget());
+  }
+}
+
+void MutableBlobStorage::GetBlobImplWhenReady(
+    const nsACString& aContentType, MutableBlobStorageCallback* aCallback) {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(aCallback);
+
+  MutexAutoLock lock(mMutex);
+
+  // GetBlob can be called just once.
+  MOZ_ASSERT(mStorageState != eClosed);
+  StorageState previousState = mStorageState;
+  mStorageState = eClosed;
+
+  if (previousState == eInTemporaryFile) {
+    if (NS_FAILED(mErrorResult)) {
+      MOZ_ASSERT(!mActor);
+
+      RefPtr<Runnable> runnable =
+          new BlobCreationDoneRunnable(this, aCallback, nullptr, mErrorResult);
+      EventTarget()->Dispatch(runnable.forget(), NS_DISPATCH_NORMAL);
+      return;
+    }
+
+    MOZ_ASSERT(mActor);
+
+    // We want to wait until all the WriteRunnable are completed. The way we do
+    // this is to go to the I/O thread and then we come back: the runnables are
+    // executed in order and this LastRunnable will be... the last one.
+    // This Runnable will also close the FD on the I/O thread.
+    RefPtr<Runnable> runnable = new LastRunnable(this, aContentType, aCallback);
+
+    // If the dispatching fails, we are shutting down and it's fine to do not
+    // run the callback.
+    Unused << DispatchToIOThread(runnable.forget());
+    return;
+  }
+
+  // If we are waiting for the temporary file, it's better to wait...
+  if (previousState == eWaitingForTemporaryFile) {
+    mPendingContentType = aContentType;
+    mPendingCallback = aCallback;
+    return;
+  }
+
+  RefPtr<BlobImpl> blobImpl;
+
+  if (mData) {
+    blobImpl = new MemoryBlobImpl(mData, mDataLen,
+                                  NS_ConvertUTF8toUTF16(aContentType));
+
+    mData = nullptr;  // The MemoryBlobImpl takes ownership of the buffer
+    mDataLen = 0;
+    mDataBufferLen = 0;
+  } else {
+    blobImpl = new EmptyBlobImpl(NS_ConvertUTF8toUTF16(aContentType));
+  }
+
+  RefPtr<BlobCreationDoneRunnable> runnable =
+      new BlobCreationDoneRunnable(this, aCallback, blobImpl, NS_OK);
+
+  nsresult error =
+      EventTarget()->Dispatch(runnable.forget(), NS_DISPATCH_NORMAL);
+  if (NS_WARN_IF(NS_FAILED(error))) {
+    return;
+  }
+}
+
+nsresult MutableBlobStorage::Append(const void* aData, uint32_t aLength) {
+  // This method can be called on any thread.
+
+  MutexAutoLock lock(mMutex);
+  MOZ_ASSERT(mStorageState != eClosed);
+  NS_ENSURE_ARG_POINTER(aData);
+
+  if (!aLength) {
+    return NS_OK;
+  }
+
+  // If eInMemory is the current Storage state, we could maybe migrate to
+  // a temporary file.
+  if (mStorageState == eInMemory && ShouldBeTemporaryStorage(lock, aLength) &&
+      !MaybeCreateTemporaryFile(lock)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  // If we are already in the temporaryFile mode, we have to dispatch a
+  // runnable.
+  if (mStorageState == eInTemporaryFile) {
+    // If a previous operation failed, let's return that error now.
+    if (NS_FAILED(mErrorResult)) {
+      return mErrorResult;
+    }
+
+    RefPtr<WriteRunnable> runnable =
+        WriteRunnable::CopyBuffer(this, aData, aLength);
+    if (NS_WARN_IF(!runnable)) {
+      return NS_ERROR_OUT_OF_MEMORY;
+    }
+
+    nsresult rv = DispatchToIOThread(runnable.forget());
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    mDataLen += aLength;
+    return NS_OK;
+  }
+
+  // By default, we store in memory.
+
+  uint64_t offset = mDataLen;
+
+  if (!ExpandBufferSize(lock, aLength)) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  memcpy((char*)mData + offset, aData, aLength);
+  return NS_OK;
+}
+
+bool MutableBlobStorage::ExpandBufferSize(const MutexAutoLock& aProofOfLock,
+                                          uint64_t aSize) {
+  MOZ_ASSERT(mStorageState < eInTemporaryFile);
+
+  if (mDataBufferLen >= mDataLen + aSize) {
+    mDataLen += aSize;
+    return true;
+  }
+
+  // Start at 1 or we'll loop forever.
+  CheckedUint32 bufferLen =
+      std::max<uint32_t>(static_cast<uint32_t>(mDataBufferLen), 1);
+  while (bufferLen.isValid() && bufferLen.value() < mDataLen + aSize) {
+    bufferLen *= 2;
+  }
+
+  if (!bufferLen.isValid()) {
+    return false;
+  }
+
+  void* data = realloc(mData, bufferLen.value());
+  if (!data) {
+    return false;
+  }
+
+  mData = data;
+  mDataBufferLen = bufferLen.value();
+  mDataLen += aSize;
+  return true;
+}
+
+bool MutableBlobStorage::ShouldBeTemporaryStorage(
+    const MutexAutoLock& aProofOfLock, uint64_t aSize) const {
+  MOZ_ASSERT(mStorageState == eInMemory);
+
+  CheckedUint32 bufferSize = mDataLen;
+  bufferSize += aSize;
+
+  if (!bufferSize.isValid()) {
+    return false;
+  }
+
+  return bufferSize.value() >= mMaxMemory;
+}
+
+bool MutableBlobStorage::MaybeCreateTemporaryFile(
+    const MutexAutoLock& aProofOfLock) {
+  mStorageState = eWaitingForTemporaryFile;
+
+  if (!NS_IsMainThread()) {
+    RefPtr<MutableBlobStorage> self = this;
+    nsCOMPtr<nsIRunnable> r = NS_NewRunnableFunction(
+        "MutableBlobStorage::MaybeCreateTemporaryFile", [self]() {
+          MutexAutoLock lock(self->mMutex);
+          self->MaybeCreateTemporaryFileOnMainThread(lock);
+          if (!self->mActor) {
+            self->ErrorPropagated(NS_ERROR_FAILURE);
+          }
+        });
+    EventTarget()->Dispatch(r.forget(), NS_DISPATCH_NORMAL);
+    return true;
+  }
+
+  MaybeCreateTemporaryFileOnMainThread(aProofOfLock);
+  return !!mActor;
+}
+
+void MutableBlobStorage::MaybeCreateTemporaryFileOnMainThread(
+    const MutexAutoLock& aProofOfLock) {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(!mActor);
+
+  mozilla::ipc::PBackgroundChild* actorChild =
+      mozilla::ipc::BackgroundChild::GetOrCreateForCurrentThread();
+  if (NS_WARN_IF(!actorChild)) {
+    return;
+  }
+
+  mActor = new TemporaryIPCBlobChild(this);
+  actorChild->SendPTemporaryIPCBlobConstructor(mActor);
+
+  // We need manually to increase the reference for this actor because the
+  // IPC allocator method is not triggered. The Release() is called by IPDL
+  // when the actor is deleted.
+  mActor.get()->AddRef();
+
+  // The actor will call us when the FileDescriptor is received.
+}
+
+void MutableBlobStorage::TemporaryFileCreated(PRFileDesc* aFD) {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  MutexAutoLock lock(mMutex);
+  MOZ_ASSERT(mStorageState == eWaitingForTemporaryFile ||
+             mStorageState == eClosed);
+  MOZ_ASSERT_IF(mPendingCallback, mStorageState == eClosed);
+  MOZ_ASSERT(mActor);
+  MOZ_ASSERT(aFD);
+
+  // If the object has been already closed and we don't need to execute a
+  // callback, we need just to close the file descriptor in the correct thread.
+  if (mStorageState == eClosed && !mPendingCallback) {
+    RefPtr<Runnable> runnable = new CloseFileRunnable(aFD);
+
+    // If this dispatching fails, CloseFileRunnable will close the FD in the
+    // DTOR on the current thread.
+    Unused << DispatchToIOThread(runnable.forget());
+
+    // Let's inform the parent that we have nothing else to do.
+    mActor->SendOperationFailed();
+    mActor = nullptr;
+    return;
+  }
+
+  // If we still receiving data, we can proceed in temporary-file mode.
+  if (mStorageState == eWaitingForTemporaryFile) {
+    mStorageState = eInTemporaryFile;
+  }
+
+  mFD = aFD;
+  MOZ_ASSERT(NS_SUCCEEDED(mErrorResult));
+
+  // This runnable takes the ownership of mData and it will write this buffer
+  // into the temporary file.
+  RefPtr<WriteRunnable> runnable =
+      WriteRunnable::AdoptBuffer(this, mData, mDataLen);
+  MOZ_ASSERT(runnable);
+
+  mData = nullptr;
+
+  nsresult rv = DispatchToIOThread(runnable.forget());
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    // Shutting down, we cannot continue.
+    return;
+  }
+
+  // If we are closed, it means that GetBlobImplWhenReady() has been called when
+  // we were already waiting for a temporary file-descriptor. Finally we are
+  // here, AdoptBuffer runnable is going to write the current buffer into this
+  // file. After that, there is nothing else to write, and we dispatch
+  // LastRunnable which ends up calling mPendingCallback via CreateBlobRunnable.
+  if (mStorageState == eClosed) {
+    MOZ_ASSERT(mPendingCallback);
+
+    RefPtr<Runnable> runnable =
+        new LastRunnable(this, mPendingContentType, mPendingCallback);
+    Unused << DispatchToIOThread(runnable.forget());
+
+    mPendingCallback = nullptr;
+  }
+}
+
+void MutableBlobStorage::AskForBlob(TemporaryIPCBlobChildCallback* aCallback,
+                                    const nsACString& aContentType) {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  MutexAutoLock lock(mMutex);
+  MOZ_ASSERT(mStorageState == eClosed);
+  MOZ_ASSERT(mFD);
+  MOZ_ASSERT(mActor);
+  MOZ_ASSERT(aCallback);
+
+  // Let's pass the FileDescriptor to the parent actor in order to keep the file
+  // locked on windows.
+  mActor->AskForBlob(aCallback, aContentType, mFD);
+
+  // The previous operation has duplicated the file descriptor. Now we can close
+  // mFD. The parent will take care of closing the duplicated file descriptor on
+  // its side.
+  RefPtr<Runnable> runnable = new CloseFileRunnable(mFD);
+  Unused << DispatchToIOThread(runnable.forget());
+
+  mFD = nullptr;
+  mActor = nullptr;
+}
+
+void MutableBlobStorage::ErrorPropagated(nsresult aRv) {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  MutexAutoLock lock(mMutex);
+  mErrorResult = aRv;
+
+  if (mActor) {
+    mActor->SendOperationFailed();
+    mActor = nullptr;
+  }
+}
+
+nsresult MutableBlobStorage::DispatchToIOThread(
+    already_AddRefed<nsIRunnable> aRunnable) {
+  if (!mTaskQueue) {
+    nsCOMPtr<nsIEventTarget> target =
+        do_GetService(NS_STREAMTRANSPORTSERVICE_CONTRACTID);
+    MOZ_ASSERT(target);
+
+    mTaskQueue = TaskQueue::Create(target.forget(), "BlobStorage");
+  }
+
+  nsCOMPtr<nsIRunnable> runnable(aRunnable);
+  nsresult rv = mTaskQueue->Dispatch(runnable.forget());
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  return NS_OK;
+}
+
+size_t MutableBlobStorage::SizeOfCurrentMemoryBuffer() {
+  MOZ_ASSERT(NS_IsMainThread());
+  MutexAutoLock lock(mMutex);
+  return mStorageState < eInTemporaryFile ? mDataLen : 0;
+}
+
+PRFileDesc* MutableBlobStorage::GetFD() {
+  MOZ_ASSERT(!NS_IsMainThread());
+  MutexAutoLock lock(mMutex);
+  return mFD;
+}
+
+void MutableBlobStorage::CloseFD() {
+  MOZ_ASSERT(!NS_IsMainThread());
+  MutexAutoLock lock(mMutex);
+  MOZ_ASSERT(mFD);
+
+  PR_Close(mFD);
+  mFD = nullptr;
+}
+
+}  // namespace mozilla::dom