JSObject*
DataViewObject::fromBuffer(JSContext* cx, HandleObject bufobj, uint32_t byteOffset, int32_t byteLength)
{
    // See TypedArrayObjectTemplate<T>::fromBufferWithProto for where this was
    // cribbed from.

    if (!ObjectClassIs(bufobj, ESClass_ArrayBuffer, cx)) {
        JS_ReportErrorNumber(cx, GetErrorMessage, nullptr, JSMSG_TYPED_ARRAY_BAD_ARGS);
        return nullptr; // must be arrayBuffer
    }

    MOZ_ASSERT(IsArrayBuffer(bufobj) || bufobj->is<ProxyObject>());
    if (bufobj->is<ProxyObject>()) {
        // Construct the new typed array in the compartment of the buffer so
        // that the DataView can point directly at the buffer data. Returns a
        // wrapper in the origin compartment for a view in the target
        // compartment directly referencing the ArrayBufferObject.
        JSObject* wrapped = CheckedUnwrap(bufobj);
        if (!wrapped) {
            JS_ReportError(cx, "Permission denied to access object");
            return nullptr;
        }
        if (IsArrayBuffer(wrapped)) {
            // Set the new view's prototype to the origin compartment's
            // prototype, not the target's.
            Rooted<JSObject*> proto(cx);
            if (!GetBuiltinPrototype(cx, JSCLASS_CACHED_PROTO_KEY(&class_), &proto))
                return nullptr;

            InvokeArgs args(cx);
            if (!args.init(3))
                return nullptr;

            args.setCallee(cx->compartment()->maybeGlobal()->createDataViewForThis());
            args.setThis(ObjectValue(*bufobj));
            args[0].setNumber(byteOffset);
            args[1].setInt32(byteLength);
            args[2].setObject(*proto);

            if (!Invoke(cx, args))
                return nullptr;
            return &args.rval().toObject();
        }
    }

    if (!IsArrayBuffer(bufobj)) {
        JS_ReportErrorNumber(cx, GetErrorMessage, nullptr, JSMSG_TYPED_ARRAY_BAD_ARGS);
        return nullptr; // must be arrayBuffer
    }

    Rooted<ArrayBufferObject*> buffer(cx, &AsArrayBuffer(bufobj));
    MOZ_ASSERT(byteOffset <= buffer->byteLength() && byteOffset + byteLength <= buffer->byteLength());
    return create(cx, byteOffset, byteLength, buffer, proto);
}