Cannot read file from filesystem

[golgobot]

I'm experimenting with loading a file asynchronously by calling a global function from JavaScript and passing a callback that gets as an argument the contents of a file on disk. The function is binded in the override function OnContextCreated shown below

Code: Select all

void MyApp::OnContextCreated(
      CefRefPtr<CefBrowser> browser,
      CefRefPtr<CefFrame> frame,
      CefRefPtr<CefV8Context> context) {
   CefRefPtr<CefV8Value> global = context->GetGlobal();
   CefRefPtr<CefV8Value> myCoolGlobal = CefV8Value::CreateObject(NULL);
   myCoolGlobal->SetValue("readFile",
         CefV8Value::CreateFunction("readFile", new ReadFile()),
         V8_PROPERTY_ATTRIBUTE_READONLY);
   global->SetValue("myCoolGlobal", myCoolGlobal, V8_PROPERTY_ATTRIBUTE_READONLY);
}


ReadFile is a V8Handler which spawns a new thread which reads a file, then posts a task to the renderer thread to execute the callback. Shown below.

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class ReadFile: public CefV8Handler {
public:
   virtual bool Execute(
         const CefString& name,
         CefRefPtr<CefV8Value> object,
         const CefV8ValueList& arguments,
         CefRefPtr<CefV8Value>& retval,
         CefString& exception) {
      std::thread t(std::bind(&ReadFile::DoReadFile, this, CefV8Context::GetCurrentContext(), arguments[0]));
      t.detach();
      return true;
   }

   void DoReadFile(CefRefPtr<CefV8Context> context, CefRefPtr<CefV8Value> callback) {
      std::string message = GetFileContents("/home/jonathan/test.txt");
      CefPostTask(
         TID_RENDERER,
         CefCreateClosureTask(base::Bind(&ReadFile::DoCallback, this, context, callback, message))
      );
   }

   void DoCallback(CefRefPtr<CefV8Context> context, CefRefPtr<CefV8Value> callback, std::string message) {
      CefV8ValueList args;
      args.push_back(CefV8Value::CreateString(message));
      callback->ExecuteFunctionWithContext(context, NULL, args);
   }

   std::string GetFileContents(const char *filename) {
      std::ifstream ifs("/home/jonathan/cef/build/cefsimple/Debug/test.txt", std::ios::in);
      if(!ifs.is_open()) {
         return "No File";
      }
      std::string str((std::istreambuf_iterator<char>(ifs)), std::istreambuf_iterator<char>());
      return str;
   }

private:
   IMPLEMENT_REFCOUNTING(ReadFile)
};


My JavaScript looks like this

Code: Select all

myCoolGlobal.readFile(
   function(message) {
      console.log(message);
   }
);


No matter what I do, ifs.is_open() always returns false. I've tried fopen, and even CefStreamReader::CreateForFile(), but non of these file io calls ever find my file.

I've tried changing ownership and permissions of my file. It's as if I can't read any files from the file system and I have no idea why.

[magreenblatt]

V8 bindings execute in the renderer process which is sandboxed and does not allow access to the file system. If you just need the file contents consider using a custom scheme handler which can return data via XMLHttpRequest: https://code.google.com/p/chromiumembed ... t_Handling. Or, if you need two-way communication, use IPC to communicate between processes with async JS callbacks: https://code.google.com/p/chromiumembed ... s_Bindings.