Bug 961665 - Native implementation of OS.File.read, native bits. r=froydnj, r=bz, r=paolo

b2g/installer/package-manifest.in

@@ -297,6 +297,7 @@
 @BINPATH@/components/storage.xpt
 @BINPATH@/components/telemetry.xpt
 @BINPATH@/components/toolkit_finalizationwitness.xpt
+@BINPATH@/components/toolkit_osfile.xpt
 @BINPATH@/components/toolkitprofile.xpt
 #ifdef MOZ_ENABLE_XREMOTE
 @BINPATH@/components/toolkitremote.xpt

browser/installer/package-manifest.in

@@ -310,6 +310,7 @@
 @BINPATH@/components/spellchecker.xpt
 @BINPATH@/components/storage.xpt
 @BINPATH@/components/toolkit_finalizationwitness.xpt
+@BINPATH@/components/toolkit_osfile.xpt
 @BINPATH@/components/toolkitprofile.xpt
 #ifdef MOZ_ENABLE_XREMOTE
 @BINPATH@/components/toolkitremote.xpt

dom/webidl/NativeOSFileInternals.webidl

@@ -0,0 +1,21 @@
+/* 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 obtaone at http://mozilla.org/MPL/2.0/. */
+
+/**
+ * Options for nsINativeOSFileInternals::Read
+ */
+dictionary NativeOSFileReadOptions
+{
+  /**
+   * If specified, convert the raw bytes to a String
+   * with the specified encoding. Otherwise, return
+   * the raw bytes as a TypedArray.
+   */
+  DOMString? encoding;
+
+  /**
+   * If specified, limit the number of bytes to read.
+   */
+  unsigned long long? bytes;
+};

dom/webidl/moz.build

@@ -244,6 +244,7 @@ WEBIDL_FILES = [
     'MozWakeLock.webidl',
     'MutationEvent.webidl',
     'MutationObserver.webidl',
+    'NativeOSFileInternals.webidl',
     'NetDashboard.webidl',
     'NetworkOptions.webidl',
     'Node.webidl',

mobile/android/installer/package-manifest.in

@@ -246,6 +246,7 @@
 @BINPATH@/components/storage.xpt
 @BINPATH@/components/telemetry.xpt
 @BINPATH@/components/toolkit_finalizationwitness.xpt
+@BINPATH@/components/toolkit_osfile.xpt
 @BINPATH@/components/toolkitprofile.xpt
 #ifdef MOZ_ENABLE_XREMOTE
 @BINPATH@/components/toolkitremote.xpt

toolkit/components/build/nsToolkitCompsModule.cpp

@@ -35,6 +35,7 @@
 
 #include "nsBrowserStatusFilter.h"
 #include "mozilla/FinalizationWitnessService.h"
+#include "mozilla/NativeOSFileInternals.h"
 
 using namespace mozilla;
 
@@ -89,6 +90,7 @@ NS_GENERIC_FACTORY_CONSTRUCTOR(nsBrowserStatusFilter)
 NS_GENERIC_FACTORY_CONSTRUCTOR(nsUpdateProcessor)
 #endif
 NS_GENERIC_FACTORY_CONSTRUCTOR(FinalizationWitnessService)
+NS_GENERIC_FACTORY_CONSTRUCTOR(NativeOSFileInternalsService)
 
 NS_DEFINE_NAMED_CID(NS_TOOLKIT_APPSTARTUP_CID);
 NS_DEFINE_NAMED_CID(NS_USERINFO_CID);
@@ -114,6 +116,7 @@ NS_DEFINE_NAMED_CID(NS_CHARSETMENU_CID);
 NS_DEFINE_NAMED_CID(NS_UPDATEPROCESSOR_CID);
 #endif
 NS_DEFINE_NAMED_CID(FINALIZATIONWITNESSSERVICE_CID);
+NS_DEFINE_NAMED_CID(NATIVE_OSFILE_INTERNALS_SERVICE_CID);
 
 static const Module::CIDEntry kToolkitCIDs[] = {
   { &kNS_TOOLKIT_APPSTARTUP_CID, false, nullptr, nsAppStartupConstructor },
@@ -140,6 +143,7 @@ static const Module::CIDEntry kToolkitCIDs[] = {
   { &kNS_UPDATEPROCESSOR_CID, false, nullptr, nsUpdateProcessorConstructor },
 #endif
   { &kFINALIZATIONWITNESSSERVICE_CID, false, nullptr, FinalizationWitnessServiceConstructor },
+  { &kNATIVE_OSFILE_INTERNALS_SERVICE_CID, false, nullptr, NativeOSFileInternalsServiceConstructor },
   { nullptr }
 };
 
@@ -169,6 +173,7 @@ static const Module::ContractIDEntry kToolkitContracts[] = {
   { NS_UPDATEPROCESSOR_CONTRACTID, &kNS_UPDATEPROCESSOR_CID },
 #endif
   { FINALIZATIONWITNESSSERVICE_CONTRACTID, &kFINALIZATIONWITNESSSERVICE_CID },
+  { NATIVE_OSFILE_INTERNALS_SERVICE_CONTRACTID, &kNATIVE_OSFILE_INTERNALS_SERVICE_CID },
   { nullptr }
 };
 

toolkit/components/osfile/NativeOSFileInternals.cpp

@@ -0,0 +1,921 @@
+/* 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/. */
+
+/**
+ * Native implementation of some OS.File operations.
+ */
+
+#include "nsString.h"
+#include "nsNetCID.h"
+#include "nsThreadUtils.h"
+#include "nsXPCOMCID.h"
+#include "nsCycleCollectionParticipant.h"
+#include "nsServiceManagerUtils.h"
+#include "nsProxyRelease.h"
+
+#include "nsINativeOSFileInternals.h"
+#include "NativeOSFileInternals.h"
+#include "mozilla/dom/NativeOSFileInternalsBinding.h"
+
+#include "nsIUnicodeDecoder.h"
+#include "nsIEventTarget.h"
+
+#include "mozilla/dom/EncodingUtils.h"
+#include "mozilla/DebugOnly.h"
+#include "mozilla/Scoped.h"
+#include "mozilla/HoldDropJSObjects.h"
+#include "mozilla/TimeStamp.h"
+
+#include "prio.h"
+#include "prerror.h"
+#include "private/pprio.h"
+
+#include "jsapi.h"
+#include "jsfriendapi.h"
+#include "js/Utility.h"
+#include "xpcpublic.h"
+
+#include <algorithm>
+#if defined(XP_UNIX)
+#include <unistd.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <sys/stat.h>
+#include <sys/uio.h>
+#endif // defined (XP_UNIX)
+
+#if defined(XP_WIN)
+#include <Windows.h>
+#endif // defined (XP_WIN)
+
+namespace mozilla {
+
+MOZ_TYPE_SPECIFIC_SCOPED_POINTER_TEMPLATE(ScopedPRFileDesc, PRFileDesc, PR_Close)
+
+namespace {
+
+// Utilities for safely manipulating ArrayBuffer contents even in the
+// absence of a JSContext.
+
+/**
+ * The C buffer underlying to an ArrayBuffer. Throughout the code, we manipulate
+ * this instead of a void* buffer, as this lets us transfer data across threads
+ * and into JavaScript without copy.
+ */
+struct ArrayBufferContents {
+  /**
+   * The header of the ArrayBuffer. This is the pointer actually used by JSAPI.
+   */
+  void* header;
+  /**
+   * The data of the ArrayBuffer. This is the pointer manipulated to
+   * read/write the contents of the buffer.
+   */
+  uint8_t* data;
+  /**
+   * The number of bytes in the ArrayBuffer.
+   */
+  size_t nbytes;
+};
+
+/**
+ * RAII for ArrayBufferContents.
+ */
+struct ScopedArrayBufferContentsTraits {
+  typedef ArrayBufferContents type;
+  const static type empty() {
+    type result = {0, 0, 0};
+    return result;
+  }
+  const static void release(type ptr) {
+    js_free(ptr.header);
+    ptr.header = nullptr;
+    ptr.data = nullptr;
+    ptr.nbytes = 0;
+  }
+};
+
+struct ScopedArrayBufferContents: public Scoped<ScopedArrayBufferContentsTraits> {
+  ScopedArrayBufferContents(MOZ_GUARD_OBJECT_NOTIFIER_ONLY_PARAM):
+    Scoped<ScopedArrayBufferContentsTraits>(MOZ_GUARD_OBJECT_NOTIFIER_ONLY_PARAM_TO_PARENT)
+  { }
+  ScopedArrayBufferContents(const ArrayBufferContents& v
+                            MOZ_GUARD_OBJECT_NOTIFIER_PARAM):
+    Scoped<ScopedArrayBufferContentsTraits>(v MOZ_GUARD_OBJECT_NOTIFIER_PARAM_TO_PARENT)
+  { }
+  ScopedArrayBufferContents& operator=(ArrayBufferContents ptr) {
+    Scoped<ScopedArrayBufferContentsTraits>::operator=(ptr);
+    return *this;
+  }
+
+  /**
+   * Request memory for this ArrayBufferContent. This memory may later
+   * be used to create an ArrayBuffer object (possibly on another
+   * thread) without copy.
+   *
+   * @return true In case of success, false otherwise.
+   */
+  bool Allocate(uint32_t length) {
+    dispose();
+    ArrayBufferContents& value = rwget();
+    if (JS_AllocateArrayBufferContents(/*no context available*/nullptr,
+                                       length,
+                                       &value.header,
+                                       &value.data)) {
+      value.nbytes = length;
+      return true;
+    }
+    return false;
+  }
+private:
+  explicit ScopedArrayBufferContents(ScopedArrayBufferContents& source) MOZ_DELETE;
+  ScopedArrayBufferContents& operator=(ScopedArrayBufferContents& source) MOZ_DELETE;
+};
+
+///////// Cross-platform issues
+
+// Platform specific constants. As OS.File always uses OS-level
+// errors, we need to map a few high-level errors to OS-level
+// constants.
+#if defined(XP_UNIX)
+#define OS_ERROR_NOMEM ENOMEM
+#define OS_ERROR_INVAL EINVAL
+#define OS_ERROR_TOO_LARGE EFBIG
+#define OS_ERROR_RACE EIO
+#elif defined(XP_WIN)
+#define OS_ERROR_NOMEM ERROR_NOT_ENOUGH_MEMORY
+#define OS_ERROR_INVAL ERROR_BAD_ARGUMENTS
+#define OS_ERROR_TOO_LARGE ERROR_FILE_TOO_LARGE
+#define OS_ERROR_RACE ERROR_SHARING_VIOLATION
+#else
+#error "We do not have platform-specific constants for this platform"
+#endif
+
+///////// Results of OS.File operations
+
+/**
+ * Base class for results passed to the callbacks.
+ *
+ * This base class implements caching of JS values returned to the client.
+ * We make use of this caching in derived classes e.g. to avoid accidents
+ * when we transfer data allocated on another thread into JS. Note that
+ * this caching can lead to cycles (e.g. if a client adds a back-reference
+ * in the JS value), so we implement all Cycle Collector primitives in
+ * AbstractResult.
+ */
+class AbstractResult: public nsINativeOSFileResult {
+public:
+  NS_DECL_NSINATIVEOSFILERESULT
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS(AbstractResult)
+
+  /**
+   * Construct the result object. Must be called on the main thread
+   * as the AbstractResult is cycle-collected.
+   *
+   * @param aStartDate The instant at which the operation was
+   * requested.  Used to collect Telemetry statistics.
+   */
+  AbstractResult(TimeStamp aStartDate)
+    : mStartDate(aStartDate)
+  {
+    MOZ_ASSERT(NS_IsMainThread());
+    mozilla::HoldJSObjects(this);
+  }
+  virtual ~AbstractResult() {
+    MOZ_ASSERT(NS_IsMainThread());
+    DropJSData();
+    mozilla::DropJSObjects(this);
+  }
+
+  /**
+   * Setup the AbstractResult once data is available.
+   *
+   * @param aDispatchDate The instant at which the IO thread received
+   * the operation request. Used to collect Telemetry statistics.
+   * @param aExecutionDuration The duration of the operation on the
+   * IO thread.
+   */
+  void Init(TimeStamp aDispatchDate,
+            TimeDuration aExecutionDuration) {
+    MOZ_ASSERT(!NS_IsMainThread());
+
+    mDispatchDuration = (aDispatchDate - mStartDate);
+    mExecutionDuration = aExecutionDuration;
+  }
+
+  /**
+   * Drop any data that could lead to a cycle.
+   */
+  void DropJSData() {
+    mCachedResult = JS::UndefinedValue();
+  }
+
+protected:
+  virtual nsresult GetCacheableResult(JSContext *cx, JS::MutableHandleValue aResult) = 0;
+
+private:
+  TimeStamp mStartDate;
+  TimeDuration mDispatchDuration;
+  TimeDuration mExecutionDuration;
+  JS::Heap<JS::Value> mCachedResult;
+};
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(AbstractResult)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(AbstractResult)
+
+NS_IMPL_CYCLE_COLLECTION_CLASS(AbstractResult)
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(AbstractResult)
+  NS_INTERFACE_MAP_ENTRY(nsINativeOSFileResult)
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+NS_INTERFACE_MAP_END
+
+NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN(AbstractResult)
+  NS_IMPL_CYCLE_COLLECTION_TRACE_JSVAL_MEMBER_CALLBACK(mCachedResult)
+NS_IMPL_CYCLE_COLLECTION_TRACE_END
+
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(AbstractResult)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_SCRIPT_OBJECTS
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(AbstractResult)
+  tmp->DropJSData();
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+
+NS_IMETHODIMP
+AbstractResult::GetDispatchDurationMS(double *aDispatchDuration)
+{
+  *aDispatchDuration = mDispatchDuration.ToMilliseconds();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+AbstractResult::GetExecutionDurationMS(double *aExecutionDuration)
+{
+  *aExecutionDuration = mExecutionDuration.ToMilliseconds();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+AbstractResult::GetResult(JSContext *cx, JS::MutableHandleValue aResult)
+{
+  if (mCachedResult.isUndefined()) {
+    nsresult rv = GetCacheableResult(cx, aResult);
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+    mCachedResult = aResult;
+    return NS_OK;
+  }
+  aResult.set(mCachedResult);
+  return NS_OK;
+}
+
+/**
+ * Return a result as a string.
+ *
+ * In this implementation, attribute |result| is a string. Strings are
+ * passed to JS without copy.
+ */
+class StringResult MOZ_FINAL : public AbstractResult
+{
+public:
+  StringResult(TimeStamp aStartDate)
+    : AbstractResult(aStartDate)
+  {
+  }
+
+  /**
+   * Initialize the object once the contents of the result as available.
+   *
+   * @param aContents The string to pass to JavaScript. Ownership of the
+   * string and its contents is passed to StringResult. The string must
+   * be valid UTF-16.
+   */
+  void Init(TimeStamp aDispatchDate,
+            TimeDuration aExecutionDuration,
+            nsString& aContents) {
+    AbstractResult::Init(aDispatchDate, aExecutionDuration);
+    mContents = aContents;
+  }
+
+protected:
+  nsresult GetCacheableResult(JSContext* cx, JS::MutableHandleValue aResult) MOZ_OVERRIDE;
+
+private:
+  nsString mContents;
+};
+
+nsresult
+StringResult::GetCacheableResult(JSContext* cx, JS::MutableHandleValue aResult)
+{
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(mContents.get());
+
+  // Convert mContents to a js string without copy. Note that this
+  // may have the side-effect of stealing the contents of the string
+  // from XPCOM and into JS.
+  if (!xpc::StringToJsval(cx, mContents, aResult)) {
+    return NS_ERROR_FAILURE;
+  }
+  return NS_OK;
+}
+
+
+/**
+ * Return a result as a Uint8Array.
+ *
+ * In this implementation, attribute |result| is a Uint8Array. The array
+ * is passed to JS without memory copy.
+ */
+class TypedArrayResult MOZ_FINAL : public AbstractResult
+{
+public:
+  TypedArrayResult(TimeStamp aStartDate)
+    : AbstractResult(aStartDate)
+  {
+  }
+
+  /**
+   * @param aContents The contents to pass to JS. Calling this method.
+   * transmits ownership of the ArrayBufferContents to the TypedArrayResult.
+   * Do not reuse this value anywhere else.
+   */
+  void Init(TimeStamp aDispatchDate,
+            TimeDuration aExecutionDuration,
+            ArrayBufferContents aContents) {
+    AbstractResult::Init(aDispatchDate, aExecutionDuration);
+    mContents = aContents;
+  }
+
+protected:
+  nsresult GetCacheableResult(JSContext* cx, JS::MutableHandleValue aResult) MOZ_OVERRIDE;
+private:
+  ScopedArrayBufferContents mContents;
+};
+
+nsresult
+TypedArrayResult::GetCacheableResult(JSContext* cx, JS::MutableHandle<JS::Value> aResult)
+{
+  MOZ_ASSERT(NS_IsMainThread());
+  // We cannot simply construct a typed array using contents.header as
+  // this would allow us to have several otherwise unrelated
+  // ArrayBuffers with the same underlying C buffer. As this would be
+  // very unsafe, we need to cache the result once we have it.
+
+  const ArrayBufferContents& contents = mContents.get();
+  MOZ_ASSERT(contents.data);
+
+  JS::Rooted<JSObject*>
+    arrayBuffer(cx, JS_NewArrayBufferWithContents(cx, contents.header));
+  if (!arrayBuffer) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  JS::Rooted<JSObject*>
+    result(cx, JS_NewUint8ArrayWithBuffer(cx, arrayBuffer,
+                                          0, contents.nbytes));
+  if (!result) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+  // The memory of contents has been allocated on a thread that
+  // doesn't have a JSRuntime, hence without a context. Now that we
+  // have a context, attach the memory to where it belongs.
+  JS_updateMallocCounter(cx, contents.nbytes);
+  mContents.forget();
+
+  aResult.setObject(*result);
+  return NS_OK;
+}
+
+//////// Callback events
+
+/**
+ * An event used to notify asynchronously of an error.
+ */
+class ErrorEvent MOZ_FINAL : public nsRunnable {
+public:
+  /**
+   * @param aOnSuccess The success callback.
+   * @param aOnError The error callback.
+   * @param aDiscardedResult The discarded result.
+   * @param aOperation The name of the operation, used for error reporting.
+   * @param aOSError The OS error of the operation, as returned by errno/
+   * GetLastError().
+   *
+   * Note that we pass both the success callback and the error
+   * callback, as well as the discarded result to ensure that they are
+   * all released on the main thread, rather than on the IO thread
+   * (which would hopefully segfault). Also, we pass the callbacks as
+   * alread_AddRefed to ensure that we do not manipulate main-thread
+   * only refcounters off the main thread.
+   */
+  ErrorEvent(already_AddRefed<nsINativeOSFileSuccessCallback> aOnSuccess,
+             already_AddRefed<nsINativeOSFileErrorCallback> aOnError,
+             already_AddRefed<AbstractResult> aDiscardedResult,
+             const nsACString& aOperation,
+             int32_t aOSError)
+    : mOnSuccess(aOnSuccess)
+    , mOnError(aOnError)
+    , mDiscardedResult(aDiscardedResult)
+    , mOSError(aOSError)
+    , mOperation(aOperation)
+    {
+      MOZ_ASSERT(!NS_IsMainThread());
+    }
+
+  NS_METHOD Run() {
+    MOZ_ASSERT(NS_IsMainThread());
+    (void)mOnError->Complete(mOperation, mOSError);
+
+    // Ensure that the callbacks are released on the main thread.
+    mOnSuccess = nullptr;
+    mOnError = nullptr;
+    mDiscardedResult = nullptr;
+
+    return NS_OK;
+  }
+ private:
+  // The callbacks. Maintained as nsRefPtr as they are generally
+  // xpconnect values, which cannot be manipulated with nsCOMPtr off
+  // the main thread. We store both the success callback and the
+  // error callback to ensure that they are safely released on the
+  // main thread.
+  nsRefPtr<nsINativeOSFileSuccessCallback> mOnSuccess;
+  nsRefPtr<nsINativeOSFileErrorCallback> mOnError;
+  nsRefPtr<AbstractResult> mDiscardedResult;
+  int32_t mOSError;
+  nsCString mOperation;
+};
+
+/**
+ * An event used to notify of a success.
+ */
+class SuccessEvent MOZ_FINAL : public nsRunnable {
+public:
+  /**
+   * @param aOnSuccess The success callback.
+   * @param aOnError The error callback.
+   *
+   * Note that we pass both the success callback and the error
+   * callback to ensure that they are both released on the main
+   * thread, rather than on the IO thread (which would hopefully
+   * segfault). Also, we pass them as alread_AddRefed to ensure that
+   * we do not manipulate xpconnect refcounters off the main thread
+   * (which is illegal).
+   */
+  SuccessEvent(already_AddRefed<nsINativeOSFileSuccessCallback> aOnSuccess,
+               already_AddRefed<nsINativeOSFileErrorCallback> aOnError,
+               already_AddRefed<nsINativeOSFileResult> aResult)
+    : mOnSuccess(aOnSuccess)
+    , mOnError(aOnError)
+    , mResult(aResult)
+    {
+      MOZ_ASSERT(!NS_IsMainThread());
+    }
+
+  NS_METHOD Run() {
+    MOZ_ASSERT(NS_IsMainThread());
+    (void)mOnSuccess->Complete(mResult);
+
+    // Ensure that the callbacks are released on the main thread.
+    mOnSuccess = nullptr;
+    mOnError = nullptr;
+    mResult = nullptr;
+
+    return NS_OK;
+  }
+ private:
+  // The callbacks. Maintained as nsRefPtr as they are generally
+  // xpconnect values, which cannot be manipulated with nsCOMPtr off
+  // the main thread. We store both the success callback and the
+  // error callback to ensure that they are safely released on the
+  // main thread.
+  nsRefPtr<nsINativeOSFileSuccessCallback> mOnSuccess;
+  nsRefPtr<nsINativeOSFileErrorCallback> mOnError;
+  nsRefPtr<nsINativeOSFileResult> mResult;
+};
+
+
+//////// Action events
+
+/**
+ * Base class shared by actions.
+ */
+class AbstractDoEvent: public nsRunnable {
+public:
+  AbstractDoEvent(already_AddRefed<nsINativeOSFileSuccessCallback> aOnSuccess,
+                  already_AddRefed<nsINativeOSFileErrorCallback> aOnError)
+    : mOnSuccess(aOnSuccess)
+    , mOnError(aOnError)
+#if defined(DEBUG)
+    , mResolved(false)
+#endif // defined(DEBUG)
+  {
+    MOZ_ASSERT(NS_IsMainThread());
+  }
+
+  /**
+   * Fail, asynchronously.
+   */
+  void Fail(const nsACString& aOperation,
+            already_AddRefed<AbstractResult> aDiscardedResult,
+            int32_t aOSError = 0) {
+    Resolve();
+    nsRefPtr<ErrorEvent> event = new ErrorEvent(mOnSuccess.forget(),
+                                                mOnError.forget(),
+                                                aDiscardedResult,
+                                                aOperation,
+                                                aOSError);
+    nsresult rv = NS_DispatchToMainThread(event, NS_DISPATCH_NORMAL);
+    if (NS_FAILED(rv)) {
+      // Last ditch attempt to release on the main thread - some of
+      // the members of event are not thread-safe, so letting the
+      // pointer go out of scope would cause a crash.
+      nsCOMPtr<nsIThread> main = do_GetMainThread();
+      NS_ProxyRelease(main, event);
+    }
+  }
+
+  /**
+   * Succeed, asynchronously.
+   */
+  void Succeed(already_AddRefed<nsINativeOSFileResult> aResult) {
+    Resolve();
+    nsRefPtr<SuccessEvent> event = new SuccessEvent(mOnSuccess.forget(),
+                                                    mOnError.forget(),
+                                                    aResult);
+    nsresult rv = NS_DispatchToMainThread(event, NS_DISPATCH_NORMAL);
+    if (NS_FAILED(rv)) {
+      // Last ditch attempt to release on the main thread - some of
+      // the members of event are not thread-safe, so letting the
+      // pointer go out of scope would cause a crash.
+      nsCOMPtr<nsIThread> main = do_GetMainThread();
+      NS_ProxyRelease(main, event);
+    }
+
+  }
+
+private:
+
+  /**
+   * Mark the event as complete, for debugging purposes.
+   */
+  void Resolve() {
+#if defined(DEBUG)
+    MOZ_ASSERT(!mResolved);
+    mResolved = true;
+#endif // defined(DEBUG)
+  }
+
+private:
+  nsRefPtr<nsINativeOSFileSuccessCallback> mOnSuccess;
+  nsRefPtr<nsINativeOSFileErrorCallback> mOnError;
+#if defined(DEBUG)
+  // |true| once the action is complete
+  bool mResolved;
+#endif // defined(DEBUG)
+};
+
+/**
+ * An abstract event implementing reading from a file.
+ *
+ * Concrete subclasses are responsible for handling the
+ * data obtained from the file and possibly post-processing it.
+ */
+class AbstractReadEvent: public AbstractDoEvent {
+public:
+  /**
+   * @param aPath The path of the file.
+   */
+  AbstractReadEvent(const nsAString& aPath,
+                    const uint64_t aBytes,
+                    already_AddRefed<nsINativeOSFileSuccessCallback> aOnSuccess,
+                    already_AddRefed<nsINativeOSFileErrorCallback>  aOnError)
+    : AbstractDoEvent(aOnSuccess, aOnError)
+    , mPath(aPath)
+    , mBytes(aBytes)
+  {
+    MOZ_ASSERT(NS_IsMainThread());
+  }
+
+  NS_METHOD Run() MOZ_OVERRIDE {
+    MOZ_ASSERT(!NS_IsMainThread());
+    TimeStamp dispatchDate = TimeStamp::Now();
+
+    nsresult rv = BeforeRead();
+    if (NS_FAILED(rv)) {
+      // Error reporting is handled by BeforeRead();
+      return NS_OK;
+    }
+
+    ScopedArrayBufferContents buffer;
+    rv = Read(buffer);
+    if (NS_FAILED(rv)) {
+      // Error reporting is handled by Read();
+      return NS_OK;
+    }
+
+    AfterRead(dispatchDate, buffer);
+    return NS_OK;
+  }
+
+ private:
+  /**
+   * Read synchronously.
+   *
+   * Must be called off the main thread.
+   *
+   * @param aBuffer The destination buffer.
+   */
+  nsresult Read(ScopedArrayBufferContents& aBuffer)
+  {
+    MOZ_ASSERT(!NS_IsMainThread());
+
+    ScopedPRFileDesc file;
+#if defined(XP_WIN)
+    // On Windows, we can't use PR_OpenFile because it doesn't
+    // handle UTF-16 encoding, which is pretty bad. In addition,
+    // PR_OpenFile opens files without sharing, which is not the
+    // general semantics of OS.File.
+    HANDLE handle =
+      ::CreateFileW(mPath.get(),
+                    GENERIC_READ,
+                    FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE,
+                    /*Security attributes*/nullptr,
+                    OPEN_EXISTING,
+                    FILE_ATTRIBUTE_NORMAL | FILE_FLAG_SEQUENTIAL_SCAN,
+                    /*Template file*/ nullptr);
+
+    if (handle == INVALID_HANDLE_VALUE) {
+      Fail(NS_LITERAL_CSTRING("open"), nullptr, ::GetLastError());
+      return NS_ERROR_FAILURE;
+    }
+
+    file = PR_ImportFile((PROsfd)handle);
+    if (!file) {
+      // |file| is closed by PR_ImportFile
+      Fail(NS_LITERAL_CSTRING("ImportFile"), nullptr, PR_GetOSError());
+      return NS_ERROR_FAILURE;
+    }
+
+#else
+    // On other platforms, PR_OpenFile will do.
+    NS_ConvertUTF16toUTF8 path(mPath);
+    file = PR_OpenFile(path.get(), PR_RDONLY, 0);
+    if (!file) {
+      Fail(NS_LITERAL_CSTRING("open"), nullptr, PR_GetOSError());
+      return NS_ERROR_FAILURE;
+    }
+
+#endif // defined(XP_XIN)
+
+    PRFileInfo64 stat;
+    if (PR_GetOpenFileInfo64(file, &stat) != PR_SUCCESS) {
+      Fail(NS_LITERAL_CSTRING("stat"), nullptr, PR_GetOSError());
+      return NS_ERROR_FAILURE;
+    }
+
+    uint64_t bytes = std::min((uint64_t)stat.size, mBytes);
+    if (bytes > UINT32_MAX) {
+      Fail(NS_LITERAL_CSTRING("Arithmetics"), nullptr, OS_ERROR_INVAL);
+      return NS_ERROR_FAILURE;
+    }
+
+    if (!aBuffer.Allocate(bytes)) {
+      Fail(NS_LITERAL_CSTRING("allocate"), nullptr, OS_ERROR_NOMEM);
+      return NS_ERROR_FAILURE;
+    }
+
+    uint64_t total_read = 0;
+    int32_t just_read = 0;
+    char* dest_chars = reinterpret_cast<char*>(aBuffer.rwget().data);
+    do {
+      just_read = PR_Read(file, dest_chars + total_read,
+                          std::min(uint64_t(PR_INT32_MAX), bytes - total_read));
+      if (just_read == -1) {
+        Fail(NS_LITERAL_CSTRING("read"), nullptr, PR_GetOSError());
+        return NS_ERROR_FAILURE;
+      }
+      total_read += just_read;
+    } while (just_read != 0 && total_read < bytes);
+    if (total_read != bytes) {
+      // We seem to have a race condition here.
+      Fail(NS_LITERAL_CSTRING("read"), nullptr, OS_ERROR_RACE);
+      return NS_ERROR_FAILURE;
+    }
+
+    return NS_OK;
+  }
+
+protected:
+  /**
+   * Any steps that need to be taken before reading.
+   *
+   * In case of error, this method should call Fail() and return
+   * a failure code.
+   */
+  virtual
+  nsresult BeforeRead() {
+    return NS_OK;
+  }
+
+  /**
+   * Proceed after reading.
+   */
+  virtual
+  void AfterRead(TimeStamp aDispatchDate, ScopedArrayBufferContents& aBuffer) = 0;
+
+ protected:
+  const nsString mPath;
+  const uint64_t mBytes;
+};
+
+/**
+ * An implementation of a Read event that provides the data
+ * as a TypedArray.
+ */
+class DoReadToTypedArrayEvent MOZ_FINAL : public AbstractReadEvent {
+public:
+  DoReadToTypedArrayEvent(const nsAString& aPath,
+                          const uint32_t aBytes,
+                          already_AddRefed<nsINativeOSFileSuccessCallback> aOnSuccess,
+                          already_AddRefed<nsINativeOSFileErrorCallback>  aOnError)
+    : AbstractReadEvent(aPath, aBytes,
+                        aOnSuccess, aOnError)
+    , mResult(new TypedArrayResult(TimeStamp::Now()))
+  { }
+
+  ~DoReadToTypedArrayEvent() {
+    // If AbstractReadEvent::Run() has bailed out, we may need to cleanup
+    // mResult, which is main-thread only data
+    if (!mResult) {
+      return;
+    }
+    nsCOMPtr<nsIThread> main = do_GetMainThread();
+    (void)NS_ProxyRelease(main, mResult);
+  }
+
+protected:
+  void AfterRead(TimeStamp aDispatchDate,
+                 ScopedArrayBufferContents& aBuffer) MOZ_OVERRIDE {
+    MOZ_ASSERT(!NS_IsMainThread());
+    mResult->Init(aDispatchDate, TimeStamp::Now() - aDispatchDate, aBuffer.forget());
+    Succeed(mResult.forget());
+  }
+
+ private:
+  nsRefPtr<TypedArrayResult> mResult;
+};
+
+/**
+ * An implementation of a Read event that provides the data
+ * as a JavaScript string.
+ */
+class DoReadToStringEvent MOZ_FINAL : public AbstractReadEvent {
+public:
+  DoReadToStringEvent(const nsAString& aPath,
+                      const nsACString& aEncoding,
+                      const uint32_t aBytes,
+                      already_AddRefed<nsINativeOSFileSuccessCallback> aOnSuccess,
+                      already_AddRefed<nsINativeOSFileErrorCallback>  aOnError)
+    : AbstractReadEvent(aPath, aBytes, aOnSuccess, aOnError)
+    , mEncoding(aEncoding)
+    , mResult(new StringResult(TimeStamp::Now()))
+  { }
+
+  ~DoReadToStringEvent() {
+    // If AbstraactReadEvent::Run() has bailed out, we may need to cleanup
+    // mResult, which is main-thread only data
+    if (!mResult) {
+      return;
+    }
+    nsCOMPtr<nsIThread> main = do_GetMainThread();
+    (void)NS_ProxyRelease(main, mResult);
+  }
+
+protected:
+  nsresult BeforeRead() MOZ_OVERRIDE {
+    // Obtain the decoder. We do this before reading to avoid doing
+    // any unnecessary I/O in case the name of the encoding is incorrect.
+    MOZ_ASSERT(!NS_IsMainThread());
+    nsAutoCString encodingName;
+    if (!dom::EncodingUtils::FindEncodingForLabel(mEncoding, encodingName)) {
+      Fail(NS_LITERAL_CSTRING("Decode"), mResult.forget(), OS_ERROR_INVAL);
+      return NS_ERROR_FAILURE;
+    }
+    mDecoder = dom::EncodingUtils::DecoderForEncoding(encodingName);
+    if (!mDecoder) {
+      Fail(NS_LITERAL_CSTRING("DecoderForEncoding"), mResult.forget(), OS_ERROR_INVAL);
+      return NS_ERROR_FAILURE;
+    }
+
+    return NS_OK;
+  }
+
+  void AfterRead(TimeStamp aDispatchDate,
+                 ScopedArrayBufferContents& aBuffer) MOZ_OVERRIDE {
+    MOZ_ASSERT(!NS_IsMainThread());
+
+    int32_t maxChars;
+    const char* sourceChars = reinterpret_cast<const char*>(aBuffer.get().data);
+    int32_t sourceBytes = aBuffer.get().nbytes;
+    if (sourceBytes < 0) {
+      Fail(NS_LITERAL_CSTRING("arithmetics"), mResult.forget(), OS_ERROR_TOO_LARGE);
+      return;
+    }
+
+    nsresult rv = mDecoder->GetMaxLength(sourceChars, sourceBytes, &maxChars);
+    if (NS_FAILED(rv)) {
+      Fail(NS_LITERAL_CSTRING("GetMaxLength"), mResult.forget(), OS_ERROR_INVAL);
+      return;
+    }
+
+    if (maxChars < 0) {
+      Fail(NS_LITERAL_CSTRING("arithmetics"), mResult.forget(), OS_ERROR_TOO_LARGE);
+      return;
+    }
+
+    nsString resultString;
+    resultString.SetLength(maxChars);
+    if (resultString.Length() != (nsString::size_type)maxChars) {
+      Fail(NS_LITERAL_CSTRING("allocation"), mResult.forget(), OS_ERROR_TOO_LARGE);
+      return;
+    }
+
+
+    rv = mDecoder->Convert(sourceChars, &sourceBytes,
+                           resultString.BeginWriting(), &maxChars);
+    MOZ_ASSERT(NS_SUCCEEDED(rv));
+    resultString.SetLength(maxChars);
+
+    mResult->Init(aDispatchDate, TimeStamp::Now() - aDispatchDate, resultString);
+    Succeed(mResult.forget());
+  }
+
+ private:
+  nsCString mEncoding;
+  nsCOMPtr<nsIUnicodeDecoder> mDecoder;
+  nsRefPtr<StringResult> mResult;
+};
+
+} // osfile
+
+// The OS.File service
+
+NS_IMPL_ISUPPORTS1(NativeOSFileInternalsService, nsINativeOSFileInternalsService);
+
+NS_IMETHODIMP
+NativeOSFileInternalsService::Read(const nsAString& aPath,
+                                   JS::HandleValue aOptions,
+                                   nsINativeOSFileSuccessCallback *aOnSuccess,
+                                   nsINativeOSFileErrorCallback *aOnError,
+                                   JSContext* cx)
+{
+  // Extract options
+  nsCString encoding;
+  uint64_t bytes = UINT64_MAX;
+
+  if (aOptions.isObject()) {
+    dom::NativeOSFileReadOptions dict;
+    if (!dict.Init(cx, aOptions)) {
+      return NS_ERROR_INVALID_ARG;
+    }
+
+    if (dict.mEncoding.WasPassed()) {
+      CopyUTF16toUTF8(dict.mEncoding.Value(), encoding);
+    }
+
+    if (dict.mBytes.WasPassed() && !dict.mBytes.Value().IsNull()) {
+      bytes = dict.mBytes.Value().Value();
+    }
+  }
+
+  // Prepare the off main thread event and dispatch it
+  nsCOMPtr<nsINativeOSFileSuccessCallback> onSuccess(aOnSuccess);
+  nsCOMPtr<nsINativeOSFileErrorCallback> onError(aOnError);
+
+  nsRefPtr<AbstractDoEvent> event;
+  if (encoding.IsEmpty()) {
+    event = new DoReadToTypedArrayEvent(aPath, bytes,
+                                        onSuccess.forget(),
+                                        onError.forget());
+  } else {
+    event = new DoReadToStringEvent(aPath, encoding, bytes,
+                                    onSuccess.forget(),
+                                    onError.forget());
+  }
+
+  nsresult rv;
+  nsCOMPtr<nsIEventTarget> target = do_GetService(NS_STREAMTRANSPORTSERVICE_CONTRACTID, &rv);
+
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+  return target->Dispatch(event, NS_DISPATCH_NORMAL);
+}
+
+} // namespace mozilla
+

toolkit/components/osfile/NativeOSFileInternals.h

@@ -0,0 +1,24 @@
+/* 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/. */
+
+#ifndef mozilla_nativeosfileinternalservice_h__
+#define mozilla_nativeosfileinternalservice_h__
+
+#include "nsINativeOSFileInternals.h"
+#include "mozilla/Attributes.h"
+
+namespace mozilla {
+
+class NativeOSFileInternalsService MOZ_FINAL : public nsINativeOSFileInternalsService {
+public:
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSINATIVEOSFILEINTERNALSSERVICE
+private:
+  // Avoid accidental use of built-in operator=
+  void operator=(const NativeOSFileInternalsService& other) MOZ_DELETE;
+};
+
+} // namespace mozilla
+
+#endif // mozilla_finalizationwitnessservice_h__

toolkit/components/osfile/moz.build

@@ -11,7 +11,22 @@ DIRS += [
 MOCHITEST_CHROME_MANIFESTS += ['tests/mochi/chrome.ini']
 XPCSHELL_TESTS_MANIFESTS += ['tests/xpcshell/xpcshell.ini']
 
+SOURCES += [
+    'NativeOSFileInternals.cpp',
+]
+
+XPIDL_MODULE = 'toolkit_osfile'
+
+XPIDL_SOURCES += [
+    'nsINativeOSFileInternals.idl',
+]
+
+EXPORTS.mozilla += [
+    'NativeOSFileInternals.h',
+]
+
 EXTRA_PP_JS_MODULES += [
     'osfile.jsm',
 ]
 
+FINAL_LIBRARY = 'toolkitcomps'

toolkit/components/osfile/nsINativeOSFileInternals.idl

@@ -0,0 +1,93 @@
+/* -*- Mode: c++; c-basic-offset: 2; indent-tabs-mode: nil; tab-width: 40 -*- */
+/* vim: set ts=2 et sw=2 tw=40: */
+/* 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 "nsISupports.idl"
+
+/**
+ * The result of a successful asynchronous operation.
+ */
+[scriptable, builtinclass, uuid(08B4CF29-3D65-4E79-B522-A694C322ED07)]
+interface nsINativeOSFileResult: nsISupports
+{
+  /**
+   * The actual value produced by the operation.
+   *
+   * Actual type of this value depends on the options passed to the
+   * operation.
+   */
+  [implicit_jscontext]
+  readonly attribute jsval result;
+
+  /**
+   * Delay between when the operation was requested on the main thread and
+   * when the operation was started off main thread.
+   */
+  readonly attribute double dispatchDurationMS;
+
+  /**
+   * Duration of the off main thread execution.
+   */
+  readonly attribute double executionDurationMS;
+};
+
+/**
+ * A callback invoked in case of success.
+ */
+[scriptable, function, uuid(2C1922CA-CA1B-4099-8B61-EC23CFF49412)]
+interface nsINativeOSFileSuccessCallback: nsISupports
+{
+  void complete(in nsINativeOSFileResult result);
+};
+
+/**
+ * A callback invoked in case of error.
+ */
+[scriptable, function, uuid(F612E0FC-6736-4D24-AA50-FD661B3B40B6)]
+interface nsINativeOSFileErrorCallback: nsISupports
+{
+  /**
+   * @param operation The name of the failed operation. Provided to aid
+   * debugging only, may change without notice.
+   * @param OSstatus The OS status of the operation (errno under Unix,
+   * GetLastError under Windows).
+   */
+  void complete(in ACString operation, in long OSstatus);
+};
+
+/**
+ * A service providing native implementations of some of the features
+ * of OS.File.
+ */
+[scriptable, builtinclass, uuid(913362AD-1526-4623-9E6B-A2EB08AFBBB9)]
+interface nsINativeOSFileInternalsService: nsISupports
+{
+  /**
+   * Implementation of OS.File.read
+   *
+   * @param path The absolute path to the file to read.
+   * @param options An object that may contain some of the following fields
+   * - {number} bytes The maximal number of bytes to read.
+   * - {string} encoding If provided, return the result as a string, decoded
+   *   using this encoding. Otherwise, pass the result as an ArrayBuffer.
+   *   Invalid encodings cause onError to be called with the platform-specific
+   *   "invalid argument" constant.
+   * - {string} compression Unimplemented at the moment.
+   * @param onSuccess The success callback.
+   * @param onError The error callback.
+   */
+  [implicit_jscontext]
+  void read(in AString path, in jsval options,
+            in nsINativeOSFileSuccessCallback onSuccess,
+            in nsINativeOSFileErrorCallback onError);
+};
+
+
+%{ C++
+
+#define NATIVE_OSFILE_INTERNALS_SERVICE_CID {0x63A69303,0x8A64,0x45A9,{0x84, 0x8C, 0xD4, 0xE2, 0x79, 0x27, 0x94, 0xE6}}
+#define NATIVE_OSFILE_INTERNALS_SERVICE_CONTRACTID "@mozilla.org/toolkit/osfile/native-internals;1"
+
+%}

xpcom/io/nsLocalFileWin.cpp

@@ -592,7 +592,7 @@ struct PRFilePrivate {
 
 // copied from nsprpub/pr/src/{io/prfile.c | md/windows/w95io.c} : 
 // PR_Open and _PR_MD_OPEN
-static nsresult
+nsresult
 OpenFile(const nsAFlatString &name, int osflags, int mode,
          PRFileDesc **fd)
 {