1 files changed, 106 insertions, 0 deletions
diff --git a/dom/streams/ByteStreamHelpers.cpp b/dom/streams/ByteStreamHelpers.cpp
new file mode 100644
index 0000000000..5022bb2c72
--- /dev/null
+++ b/dom/streams/ByteStreamHelpers.cpp
@@ -0,0 +1,106 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* 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 "mozilla/dom/ByteStreamHelpers.h"
+#include "mozilla/dom/ReadableByteStreamController.h"
+#include "js/ArrayBuffer.h"
+#include "js/RootingAPI.h"
+#include "js/experimental/TypedData.h"
+#include "mozilla/ErrorResult.h"
+
+namespace mozilla::dom {
+
+// https://streams.spec.whatwg.org/#transfer-array-buffer
+// As some parts of the specifcation want to use the abrupt completion value,
+// this function may leave a pending exception if it returns nullptr.
+JSObject* TransferArrayBuffer(JSContext* aCx, JS::Handle<JSObject*> aObject) {
+  MOZ_ASSERT(JS::IsArrayBufferObject(aObject));
+
+  // Step 1.
+  MOZ_ASSERT(!JS::IsDetachedArrayBufferObject(aObject));
+
+  // Step 3 (Reordered)
+  size_t bufferLength = JS::GetArrayBufferByteLength(aObject);
+
+  // Step 2 (Reordered)
+  UniquePtr<void, JS::FreePolicy> bufferData{
+      JS::StealArrayBufferContents(aCx, aObject)};
+
+  // Step 4.
+  if (!JS::DetachArrayBuffer(aCx, aObject)) {
+    return nullptr;
+  }
+
+  // Step 5.
+  return JS::NewArrayBufferWithContents(aCx, bufferLength,
+                                        std::move(bufferData));
+}
+
+// https://streams.spec.whatwg.org/#can-transfer-array-buffer
+bool CanTransferArrayBuffer(JSContext* aCx, JS::Handle<JSObject*> aObject,
+                            ErrorResult& aRv) {
+  // Step 1. Assert: Type(O) is Object. (Implicit in types)
+  // Step 2. Assert: O has an [[ArrayBufferData]] internal slot.
+  MOZ_ASSERT(JS::IsArrayBufferObject(aObject));
+
+  // Step 3. If ! IsDetachedBuffer(O) is true, return false.
+  if (JS::IsDetachedArrayBufferObject(aObject)) {
+    return false;
+  }
+
+  // Step 4. If SameValue(O.[[ArrayBufferDetachKey]], undefined) is false,
+  // return false.
+  // Step 5. Return true.
+  // Note: WASM memories are the only buffers that would qualify
+  // as having an [[ArrayBufferDetachKey]] which is not undefined.
+  bool hasDefinedArrayBufferDetachKey = false;
+  if (!JS::HasDefinedArrayBufferDetachKey(aCx, aObject,
+                                          &hasDefinedArrayBufferDetachKey)) {
+    aRv.StealExceptionFromJSContext(aCx);
+    return false;
+  }
+  return !hasDefinedArrayBufferDetachKey;
+}
+
+// https://streams.spec.whatwg.org/#abstract-opdef-cloneasuint8array
+JSObject* CloneAsUint8Array(JSContext* aCx, JS::Handle<JSObject*> aObject) {
+  // Step 1. Assert: Type(O) is Object. Implicit.
+  // Step 2. Assert: O has an [[ViewedArrayBuffer]] internal slot.
+  MOZ_ASSERT(JS_IsArrayBufferViewObject(aObject));
+
+  // Step 3. Assert: !IsDetachedBuffer(O.[[ViewedArrayBuffer]]) is false.
+  bool isShared;
+  JS::Rooted<JSObject*> viewedArrayBuffer(
+      aCx, JS_GetArrayBufferViewBuffer(aCx, aObject, &isShared));
+  if (!viewedArrayBuffer) {
+    return nullptr;
+  }
+  MOZ_ASSERT(!JS::IsDetachedArrayBufferObject(viewedArrayBuffer));
+
+  // Step 4. Let buffer be ?CloneArrayBuffer(O.[[ViewedArrayBuffer]],
+  //         O.[[ByteOffset]], O.[[ByteLength]], %ArrayBuffer%).
+  size_t byteOffset = JS_GetTypedArrayByteOffset(aObject);
+  size_t byteLength = JS_GetTypedArrayByteLength(aObject);
+  JS::Rooted<JSObject*> buffer(
+      aCx,
+      JS::ArrayBufferClone(aCx, viewedArrayBuffer, byteOffset, byteLength));
+  if (!buffer) {
+    return nullptr;
+  }
+
+  // Step 5. Let array be ! Construct(%Uint8Array%, « buffer »).
+  JS::Rooted<JSObject*> array(
+      aCx, JS_NewUint8ArrayWithBuffer(aCx, buffer, 0,
+                                      static_cast<int64_t>(byteLength)));
+  if (!array) {
+    return nullptr;
+  }
+
+  // Step 6. Return array.
+  return array;
+}
+
+}  // namespace mozilla::dom