Issue #4692 - Rewrite I/O tasks to avoid engine self-reference

src/FileSystemJsObject.cpp

Index: src/FileSystemJsObject.cpp
===================================================================
--- a/src/FileSystemJsObject.cpp
+++ b/src/FileSystemJsObject.cpp
@@ -23,47 +23,40 @@
 #include <AdblockPlus/JsValue.h>
 #include "FileSystemJsObject.h"
 #include "JsContext.h"
+#include "JsEngineTransition.h"
 #include "Scheduler.h"
 #include "Utils.h"
+#include "Value.h"
 
 using namespace AdblockPlus;
 
 namespace
 {
-  class IoTask
+  class ReadTask
   {
-  protected:
-    virtual void operator()() = 0;
+    /**
+     * Shared pointer keeps engine in existence for task thread.
+     */
     JsEnginePtr jsEngine;
-    FileSystemPtr fileSystem;
-    JsValuePtr callback;
+    std::string path;
+    V8PersistentNG<v8::Function> callbackFunction;
 
   public:
-    IoTask(JsEnginePtr jsEngine, JsValuePtr callback)
-      : jsEngine(jsEngine), fileSystem(jsEngine->GetFileSystem()),
-        callback(callback)
-    {
-    }
-
-    virtual ~IoTask() {}
-  };
-
-  class ReadTask : public IoTask
-  {
-  public:
-    ReadTask(JsEnginePtr jsEngine, JsValuePtr callback,
-               const std::string& path)
-      : IoTask(jsEngine, callback), path(path)
-    {
-    }
+    ReadTask(JsEngineInternal* engine, const std::string& path,
+      V8PersistentNG<v8::Function> callbackFunction)
+      : jsEngine(engine->shared_from_this()), path(path),
+      callbackFunction(callbackFunction)
+    {}
 
     void operator()()
     {
+      JsEngineInternal* engine = ToInternal(jsEngine);
       std::string content;
       std::string error;
+      // Read operation is long-lived. Do not lock engine during it.
       try
       {
-        std::shared_ptr<std::istream> stream = fileSystem->Read(path);
+        std::shared_ptr<std::istream> stream = engine->GetFileSystem()->Read(path);
         content = Utils::Slurp(*stream);
       }
       catch (std::exception& e)
@@ -72,39 +65,46 @@
       }
       catch (...)
       {
-        error =  "Unknown error while reading from " + path;
+        error = "Unknown error while reading from " + path;
       }
-
-      const JsContext context(jsEngine);
-      JsValuePtr result = jsEngine->NewObject();
-      result->SetProperty("content", content);
-      result->SetProperty("error", error);
-      JsValueList params;
-      params.push_back(result);
-      callback->Call(params);
+      // Call back with the results of the read operation
+      V8ExecutionScope scope(engine);
+      auto callbackArguments = v8::Object::New();
+      callbackArguments->Set(engine->ToV8String("content"), engine->ToV8String(content));
+      callbackArguments->Set(engine->ToV8String("error"), engine->ToV8String(error));
+      auto args = AllocatedArray<v8::Local<v8::Value>>(1);
+      args[0] = callbackArguments;
+      engine->ApplyFunction(callbackFunction.Get(engine->GetIsolate()), std::move(args));
     }
-
-  private:
-    std::string path;
   };
 
-  class WriteTask : public IoTask
+  class WriteTask
   {
+    /**
+     * Shared pointer keeps engine in existence for task thread.
+     */
+    JsEnginePtr jsEngine;
+    std::string path;
+    std::string content;
+    V8PersistentNG<v8::Function> callbackFunction;
   public:
-    WriteTask(JsEnginePtr jsEngine, JsValuePtr callback,
-                const std::string& path, const std::string& content)
-      : IoTask(jsEngine, callback), path(path), content(content)
-    {
-    }
+    WriteTask(JsEngineInternal* engine,
+      const std::string& path, const std::string& content,
+      V8PersistentNG<v8::Function> callbackFunction)
+      : jsEngine(engine->shared_from_this()), path(path), content(content),
+      callbackFunction(callbackFunction)
+    {}
 
     void operator()()
     {
+      JsEngineInternal* engine = ToInternal(jsEngine);
       std::string error;
+      // Write operation is long-lived. Do not lock engine during it.
       try
       {
         std::shared_ptr<std::iostream> stream(new std::stringstream);
         *stream << content;
-        fileSystem->Write(path, stream);
+        engine->GetFileSystem()->Write(path, stream);
       }
       catch (std::exception& e)
       {
@@ -114,34 +114,38 @@
       {
         error = "Unknown error while writing to " + path;
       }
-
-      const JsContext context(jsEngine);
-      JsValuePtr errorValue = jsEngine->NewValue(error);
-      JsValueList params;
-      params.push_back(errorValue);
-      callback->Call(params);
+      // Apply the callback function
+      V8ExecutionScope scope(engine);
+      auto args = AllocatedArray<v8::Local<v8::Value>>(1);
+      args[0] = engine->ToV8String(error);
+      engine->ApplyFunction(callbackFunction.Get(engine->GetIsolate()), std::move(args));
     }
-
-  private:
-    std::string path;
-    std::string content;
   };
 
-  class MoveTask : public IoTask
+  class MoveTask
   {
+    /**
+     * Shared pointer keeps engine in existence for task thread.
+     */
+    JsEnginePtr jsEngine;
+    std::string fromPath;
+    std::string toPath;
+    V8PersistentNG<v8::Function> callbackFunction;
+
   public:
-    MoveTask(JsEnginePtr jsEngine, JsValuePtr callback,
-               const std::string& fromPath, const std::string& toPath)
-      : IoTask(jsEngine, callback), fromPath(fromPath), toPath(toPath)
-    {
-    }
+    MoveTask(JsEngineInternal* engine, const std::string& fromPath, const std::string& toPath,
+      V8PersistentNG<v8::Function> callbackFunction)
+      : jsEngine(engine->shared_from_this()), fromPath(fromPath), toPath(toPath), 
+      callbackFunction(callbackFunction)
+    {}
 
     void operator()()
     {
+      JsEngineInternal* engine(ToInternal(jsEngine));
       std::string error;
       try
       {
-        fileSystem->Move(fromPath, toPath);
+        engine->GetFileSystem()->Move(fromPath, toPath);
       }
       catch (std::exception& e)
       {
@@ -151,34 +155,36 @@
       {
         error = "Unknown error while moving " + fromPath + " to " + toPath;
       }
-
-      const JsContext context(jsEngine);
-      JsValuePtr errorValue = jsEngine->NewValue(error);
-      JsValueList params;
-      params.push_back(errorValue);
-      callback->Call(params);
+      V8ExecutionScope scope(engine);
+      auto args = AllocatedArray<v8::Local<v8::Value>>(1);
+      args[0] = engine->ToV8String(error);
+      engine->ApplyFunction(callbackFunction.Get(engine->GetIsolate()), std::move(args));
     }
-
-  private:
-    std::string fromPath;
-    std::string toPath;
   };
 
-  class RemoveTask : public IoTask
+  class RemoveTask
   {
+    /**
+     * Shared pointer keeps engine in existence for task thread.
+     */
+    JsEnginePtr jsEngine;
+    std::string path;
+    V8PersistentNG<v8::Function> callbackFunction;
+
   public:
-    RemoveTask(JsEnginePtr jsEngine, JsValuePtr callback,
-                 const std::string& path)
-      : IoTask(jsEngine, callback), path(path)
-    {
-    }
+    RemoveTask(JsEngineInternal *engine, const std::string& path,
+      V8PersistentNG<v8::Function> callbackFunction)
+      : jsEngine(engine->shared_from_this()), path(path),
+      callbackFunction(callbackFunction)
+    {}
 
     void operator()()
     {
+      JsEngineInternal* engine(ToInternal(jsEngine));
       std::string error;
       try
       {
-        fileSystem->Remove(path);
+        engine->GetFileSystem()->Remove(path);
       }
       catch (std::exception& e)
       {
@@ -188,35 +194,37 @@
       {
         error = "Unknown error while removing " + path;
       }
-
-      const JsContext context(jsEngine);
-      JsValuePtr errorValue = jsEngine->NewValue(error);
-      JsValueList params;
-      params.push_back(errorValue);
-      callback->Call(params);
+      V8ExecutionScope scope(engine);
+      auto args = AllocatedArray<v8::Local<v8::Value>>(1);
+      args[0] = engine->ToV8String(error);
+      engine->ApplyFunction(callbackFunction.Get(engine->GetIsolate()), std::move(args));
     }
-
-  private:
-    std::string path;
   };
 
+  class StatTask
+  {
+    /**
+     * Shared pointer keeps engine in existence for task thread.
+     */
+    JsEnginePtr jsEngine;
+    std::string path;
+    V8PersistentNG<v8::Function> callbackFunction;
 
-  class StatTask : public IoTask
-  {
   public:
-    StatTask(JsEnginePtr jsEngine, JsValuePtr callback,
-               const std::string& path)
-      : IoTask(jsEngine, callback), path(path)
-    {
-    }
+    StatTask(JsEngineInternal* engine, const std::string& path,
+      V8PersistentNG<v8::Function> callbackFunction)
+      : jsEngine(engine->shared_from_this()), path(path),
+      callbackFunction(callbackFunction)
+    {}
 
     void operator()()
     {
+      JsEngineInternal* engine(ToInternal(jsEngine));
       std::string error;
       FileSystem::StatResult statResult;
       try
       {
-        statResult = fileSystem->Stat(path);
+        statResult = engine->GetFileSystem()->Stat(path);
       }
       catch (std::exception& e)
       {
@@ -226,139 +234,221 @@
       {
         error = "Unknown error while calling stat on " + path;
       }
-
-      const JsContext context(jsEngine);
-      JsValuePtr result = jsEngine->NewObject();
-      result->SetProperty("exists", statResult.exists);
-      result->SetProperty("isFile", statResult.isFile);
-      result->SetProperty("isDirectory", statResult.isDirectory);
-      result->SetProperty("lastModified", statResult.lastModified);
-      result->SetProperty("error", error);
-
-      JsValueList params;
-      params.push_back(result);
-      callback->Call(params);
+      V8ExecutionScope scope(engine);
+      auto callbackArgument(v8::Object::New());
+      callbackArgument->Set(engine->ToV8String("exists"), v8::Boolean::New(statResult.exists));
+      callbackArgument->Set(engine->ToV8String("isFile"), v8::Boolean::New(statResult.isFile));
+      callbackArgument->Set(engine->ToV8String("isDirectory"), v8::Boolean::New(statResult.isDirectory));
+      callbackArgument->Set(engine->ToV8String("lastModified"), v8::Number::New(statResult.lastModified));
+      callbackArgument->Set(engine->ToV8String("error"), engine->ToV8String(error));
+      auto args = AllocatedArray<v8::Local<v8::Value>>(1);
+      args[0] = callbackArgument;
+      engine->ApplyFunction(callbackFunction.Get(engine->GetIsolate()), std::move(args));
     }
-
-  private:
-    std::string path;
   };
-
-  v8::Handle<v8::Value> ReadCallback(const v8::Arguments& arguments)
-  {
-    AdblockPlus::JsEnginePtr jsEngine = AdblockPlus::JsEngine::FromArguments(arguments);
-    AdblockPlus::JsValueList converted = jsEngine->ConvertArguments(arguments);
-
-    v8::Isolate* isolate = arguments.GetIsolate();
-    if (converted.size() != 2)
-      return v8::ThrowException(Utils::ToV8String(isolate,
-        "_fileSystem.read requires 2 parameters"));
-    if (!converted[1]->IsFunction())
-      return v8::ThrowException(Utils::ToV8String(isolate,
-        "Second argument to _fileSystem.read must be a function"));
-    const auto readTask = std::make_shared<ReadTask>(jsEngine, converted[1],
-        converted[0]->AsString());
-    jsEngine->Schedule(AdblockPlus::MakeHeapFunction(readTask), AdblockPlus::ImmediateSingleUseThread);
-    return v8::Undefined();
-  }
-
-  v8::Handle<v8::Value> WriteCallback(const v8::Arguments& arguments)
-  {
-    AdblockPlus::JsEnginePtr jsEngine = AdblockPlus::JsEngine::FromArguments(arguments);
-    AdblockPlus::JsValueList converted = jsEngine->ConvertArguments(arguments);
-
-    v8::Isolate* isolate = arguments.GetIsolate();
-    if (converted.size() != 3)
-      return v8::ThrowException(Utils::ToV8String(isolate,
-        "_fileSystem.write requires 3 parameters"));
-    if (!converted[2]->IsFunction())
-      return v8::ThrowException(Utils::ToV8String(isolate,
-        "Third argument to _fileSystem.write must be a function"));
-    const auto writeTask = std::make_shared<WriteTask>(jsEngine, converted[2],
-        converted[0]->AsString(), converted[1]->AsString());
-    jsEngine->Schedule(AdblockPlus::MakeHeapFunction(writeTask), AdblockPlus::ImmediateSingleUseThread);
-    return v8::Undefined();
-  }
-
-  v8::Handle<v8::Value> MoveCallback(const v8::Arguments& arguments)
-  {
-    AdblockPlus::JsEnginePtr jsEngine = AdblockPlus::JsEngine::FromArguments(arguments);
-    AdblockPlus::JsValueList converted = jsEngine->ConvertArguments(arguments);
-
-    v8::Isolate* isolate = arguments.GetIsolate();
-    if (converted.size() != 3)
-      return v8::ThrowException(Utils::ToV8String(isolate,
-        "_fileSystem.move requires 3 parameters"));
-    if (!converted[2]->IsFunction())
-      return v8::ThrowException(Utils::ToV8String(isolate,
-        "Third argument to _fileSystem.move must be a function"));
-    const auto moveTask = std::make_shared<MoveTask>(jsEngine, converted[2],
-        converted[0]->AsString(), converted[1]->AsString());
-    jsEngine->Schedule(AdblockPlus::MakeHeapFunction(moveTask), AdblockPlus::ImmediateSingleUseThread);
-    return v8::Undefined();
-  }
-
-  v8::Handle<v8::Value> RemoveCallback(const v8::Arguments& arguments)
-  {
-    AdblockPlus::JsEnginePtr jsEngine = AdblockPlus::JsEngine::FromArguments(arguments);
-    AdblockPlus::JsValueList converted = jsEngine->ConvertArguments(arguments);
-
-    v8::Isolate* isolate = arguments.GetIsolate();
-    if (converted.size() != 2)
-      return v8::ThrowException(Utils::ToV8String(isolate,
-        "_fileSystem.remove requires 2 parameters"));
-    if (!converted[1]->IsFunction())
-      return v8::ThrowException(Utils::ToV8String(isolate,
-        "Second argument to _fileSystem.remove must be a function"));
-    const auto removeTask = std::make_shared<RemoveTask>(jsEngine, converted[1],
-        converted[0]->AsString());
-    jsEngine->Schedule(AdblockPlus::MakeHeapFunction(removeTask), AdblockPlus::ImmediateSingleUseThread);
-    return v8::Undefined();
-  }
-
-  v8::Handle<v8::Value> StatCallback(const v8::Arguments& arguments)
-  {
-    AdblockPlus::JsEnginePtr jsEngine = AdblockPlus::JsEngine::FromArguments(arguments);
-    AdblockPlus::JsValueList converted = jsEngine->ConvertArguments(arguments);
-
-    v8::Isolate* isolate = arguments.GetIsolate();
-    if (converted.size() != 2)
-      return v8::ThrowException(Utils::ToV8String(isolate,
-        "_fileSystem.stat requires 2 parameters"));
-    if (!converted[1]->IsFunction())
-      return v8::ThrowException(Utils::ToV8String(isolate,
-        "Second argument to _fileSystem.stat must be a function"));
-    const auto statTask = std::make_shared<StatTask>(jsEngine, converted[1],
-        converted[0]->AsString());
-    jsEngine->Schedule(AdblockPlus::MakeHeapFunction(statTask), AdblockPlus::ImmediateSingleUseThread);
-    return v8::Undefined();
-  }
-
-  v8::Handle<v8::Value> ResolveCallback(const v8::Arguments& arguments)
-  {
-    AdblockPlus::JsEnginePtr jsEngine = AdblockPlus::JsEngine::FromArguments(arguments);
-    AdblockPlus::JsValueList converted = jsEngine->ConvertArguments(arguments);
-
-    v8::Isolate* isolate = arguments.GetIsolate();
-    if (converted.size() != 1)
-      return v8::ThrowException(Utils::ToV8String(isolate,
-        "_fileSystem.resolve requires 1 parameter"));
-
-    std::string resolved = jsEngine->GetFileSystem()->Resolve(converted[0]->AsString());
-
-    return Utils::ToV8String(isolate, resolved);
-  }
-
 }
 
-
-JsValuePtr FileSystemJsObject::Setup(JsEnginePtr jsEngine, JsValuePtr obj)
+v8::Handle<v8::Value> ReadCallback(const v8::Arguments& arguments)
 {
-  obj->SetProperty("read", jsEngine->NewCallback(::ReadCallback));
-  obj->SetProperty("write", jsEngine->NewCallback(::WriteCallback));
-  obj->SetProperty("move", jsEngine->NewCallback(::MoveCallback));
-  obj->SetProperty("remove", jsEngine->NewCallback(::RemoveCallback));
-  obj->SetProperty("stat", jsEngine->NewCallback(::StatCallback));
-  obj->SetProperty("resolve", jsEngine->NewCallback(::ResolveCallback));
-  return obj;
+  auto engine(JsEngineInternal::ExtractEngine(arguments));
+  std::shared_ptr<ReadTask> readTask;
+  try
+  {
+    if (arguments.Length() != 2)
+    {
+      throw std::runtime_error("_fileSystem.read requires 2 parameters");
+    }
+    bool argumentIsString;
+    std::string firstArgument;
+    std::tie(argumentIsString, firstArgument) = ConvertString(arguments[0]);
+    if (!argumentIsString)
+    {
+      throw std::runtime_error("First argument to _fileSystem.read must be a string");
+    }
+    if (!arguments[1]->IsFunction())
+    {
+      throw std::runtime_error("Second argument to _fileSystem.read must be a function");
+    }
+    readTask = std::make_shared<ReadTask>(engine, firstArgument, 
+      V8PersistentNG<v8::Function>(engine->GetIsolate(), v8::Local<v8::Function>::Cast(arguments[1])));
+  }
+  catch (const std::exception& e)
+  {
+    return v8::ThrowException(engine->ToV8String(e.what()));
+  }
+  // Run the task
+  engine->Schedule(AdblockPlus::MakeHeapFunction(readTask), AdblockPlus::ImmediateSingleUseThread);
+  return v8::Undefined();
 }
+
+v8::Handle<v8::Value> WriteCallback(const v8::Arguments& arguments)
+{
+  auto engine(JsEngineInternal::ExtractEngine(arguments));
+  std::shared_ptr<WriteTask> writeTask;
+  try
+  {
+    v8::Isolate* isolate = arguments.GetIsolate();
+
+    if (arguments.Length() != 3)
+    {
+      throw std::exception("_fileSystem.write requires 3 parameters");
+    }
+    bool argumentIsString;
+    std::string firstArgument;
+    std::tie(argumentIsString, firstArgument) = ConvertString(arguments[0]);
+    if (!argumentIsString)
+    {
+      throw std::runtime_error("First argument to _fileSystem.write must be a string");
+    }
+    std::string secondArgument;
+    std::tie(argumentIsString, secondArgument) = ConvertString(arguments[1]);
+    if (!argumentIsString)
+    {
+      throw std::runtime_error("Second argument to _fileSystem.write must be a string");
+    }
+    if (!arguments[2]->IsFunction())
+    {
+      throw std::runtime_error("Third argument to _fileSystem.write must be a function");
+    }
+    writeTask = std::make_shared<WriteTask>(engine, firstArgument, secondArgument, 
+      V8PersistentNG<v8::Function>(engine->GetIsolate(), v8::Local<v8::Function>::Cast(arguments[2])));
+  }
+  catch (const std::exception& e)
+  {
+    return v8::ThrowException(engine->ToV8String(e.what()));
+  }
+  engine->Schedule(AdblockPlus::MakeHeapFunction(writeTask), AdblockPlus::ImmediateSingleUseThread);
+  return v8::Undefined();
+}
+
+v8::Handle<v8::Value> MoveCallback(const v8::Arguments& arguments)
+{
+  auto engine(JsEngineInternal::ExtractEngine(arguments));
+  std::shared_ptr<MoveTask> moveTask;
+  std::string firstArgument, secondArgument;
+  try
+  {
+    if (arguments.Length() != 3)
+    {
+      throw std::runtime_error("_fileSystem.move requires 3 parameters");
+    }
+    bool argumentIsString;
+    std::tie(argumentIsString, firstArgument) = ConvertString(arguments[0]);
+    if (!argumentIsString)
+    {
+      throw std::runtime_error("First argument to _fileSystem.write must be a string");
+    }
+    std::tie(argumentIsString, secondArgument) = ConvertString(arguments[1]);
+    if (!argumentIsString)
+    {
+      throw std::runtime_error("Second argument to _fileSystem.write must be a string");
+    }
+    if (!arguments[2]->IsFunction())
+    {
+      throw std::runtime_error("Third argument to _fileSystem.move must be a function");
+    }
+  }
+  catch (const std::exception& e)
+  {
+    return v8::ThrowException(engine->ToV8String(e.what()));
+  }
+  // Run the task
+  moveTask = std::make_shared<MoveTask>(engine, firstArgument, secondArgument, 
+    V8PersistentNG<v8::Function>(engine->GetIsolate(), v8::Local<v8::Function>::Cast(arguments[2])));
+  engine->Schedule(AdblockPlus::MakeHeapFunction(moveTask), AdblockPlus::ImmediateSingleUseThread);
+  return v8::Undefined();
+}
+
+v8::Handle<v8::Value> RemoveCallback(const v8::Arguments& arguments)
+{
+  auto engine(JsEngineInternal::ExtractEngine(arguments));
+  std::shared_ptr<RemoveTask> removeTask;
+  std::string firstArgument;
+  try
+  {
+    if (arguments.Length() != 2)
+    {
+      throw std::runtime_error("_fileSystem.remove requires 2 parameters");
+    }
+    bool argumentIsString;
+    std::tie(argumentIsString, firstArgument) = ConvertString(arguments[0]);
+    if (!argumentIsString)
+    {
+      throw std::runtime_error("First argument to _fileSystem.remove must be a string");
+    }
+    if (!arguments[1]->IsFunction())
+    {
+      throw std::runtime_error("Second argument to _fileSystem.remove must be a function");
+    }
+  }
+  catch (const std::exception& e)
+  {
+    return v8::ThrowException(engine->ToV8String(e.what()));
+  }
+  // Run the task
+  removeTask = std::make_shared<RemoveTask>(engine, firstArgument,
+    V8PersistentNG<v8::Function>(engine->GetIsolate(), v8::Local<v8::Function>::Cast(arguments[1])));
+  engine->Schedule(AdblockPlus::MakeHeapFunction(removeTask), AdblockPlus::ImmediateSingleUseThread);
+  return v8::Undefined();
+}
+
+v8::Handle<v8::Value> StatCallback(const v8::Arguments& arguments)
+{
+  auto engine(JsEngineInternal::ExtractEngine(arguments));
+  std::shared_ptr<StatTask> statTask;
+  std::string firstArgument;
+  try
+  {
+    if (arguments.Length() != 2)
+    {
+      throw std::runtime_error("_fileSystem.stat requires 2 parameters");
+    }
+    bool argumentIsString;
+    std::tie(argumentIsString, firstArgument) = ConvertString(arguments[0]);
+    if (!argumentIsString)
+    {
+      throw std::runtime_error("First argument to _fileSystem.stat must be a string");
+    }
+    if (!arguments[1]->IsFunction())
+    {
+      throw std::runtime_error("Second argument to _fileSystem.stat must be a function");
+    }
+  }
+  catch (const std::exception& e)
+  {
+    return v8::ThrowException(engine->ToV8String(e.what()));
+  }
+  // Run the task
+  statTask = std::make_shared<StatTask>(engine, firstArgument,
+    V8PersistentNG<v8::Function>(engine->GetIsolate(), v8::Local<v8::Function>::Cast(arguments[1])));
+  engine->Schedule(AdblockPlus::MakeHeapFunction(statTask), AdblockPlus::ImmediateSingleUseThread);
+  return v8::Undefined();
+}
+
+v8::Handle<v8::Value> ResolveCallback(const v8::Arguments& arguments)
+{
+  auto engine(JsEngineInternal::ExtractEngine(arguments));
+  std::string firstArgument;
+  try
+  {
+    if (arguments.Length() != 1)
+    {
+      throw std::runtime_error("_fileSystem.resolve requires 1 parameter");
+    }
+    bool argumentIsString;
+    std::tie(argumentIsString, firstArgument) = ConvertString(arguments[0]);
+    if (!argumentIsString)
+    {
+      throw std::runtime_error("First argument to _fileSystem.write must be a string");
+    }
+  }
+  catch (const std::exception& e)
+  {
+    return v8::ThrowException(engine->ToV8String(e.what()));
+  }
+  /*
+   * Make sure to perform long-lived file system operation with engine unlocked.
+   */
+  std::string resolved = engine->GetFileSystem()->Resolve(firstArgument);
+  return engine->ToV8String(resolved);
+}