Bracket-Shell Custom Native (C++) Function not being called

Question

I'm trying to create a custom C++ function which I can call from JavaScript. The function is a simple one to just resize the window.

I have the following bits in the following places:

In appshell_extensions_platform.h:

#if defined(OS_WIN)
void ResizeWindow(CefRefPtr<CefBrowser> browser, int width, int height);
#endif

In appshell_extensions_win.cpp:

void ResizeWindow(CefRefPtr<CefBrowser> browser, int width, int height) {
    OutputDebugString(L"ResizeWindow");
    CefWindowHandle hWnd = browser->GetHost()->GetWindowHandle();
    SetWindowPos(hWnd, 0, 0, 0, width, height, SWP_NOMOVE|SWP_NOZORDER|SWP_NOACTIVATE);
}

In appshell_extensions.js:

/**
  * Resize the window to the given size.
  *
  * @param {number} width
  * @param {number} height
  *
  * @return None. This is an asynchronous call that sends all return information to the callback.
 */
 native function ResizeWindow();
 appshell.app.resizeWindow = function (width, height) {
     ResizeWindow(width, height);
 };

In appshell_extensions.cpp:

} else if (message_name == "ResizeWindow") {
    // Parameters:
    //  0: int32 - width
    //  1: int32 - height
    int width = argList->GetInt(0);
    int height = argList->GetInt(1);
    ResizeWindow(browser, width, height);
}

Using Visual Studio 2012, I then Build and Debug on the Debug Win32 release. When I open the console, appshell.app.resizeWindow is there as expected. I can call it and it works just fine. If I put additional JavaScript code in the function, it also works.

To the function in appshell_extensions.cpp, I've added OutputDebugString(std::wstring(message_name.begin(), message_name.end()).c_str());. For functions other than the one I wrote, it will output the message name properly. For the one I wrote, I get nothing.

I don't get the output from the function itself either.

It appears that the message isn't actually getting to the function which processes it, but I have no clue. I'm just using the sln that came with brackets-shell (converted to 2012) to compile. Is there a build step I'm maybe missing or something?

Thanks.

Answer 1

I figured out the problem.

Apparently, in the JavaScript functions, the first parameter MUST be a callback, even if you don't use it.

Changing the JavaScript portion to this fixed the problem:

/**
  * Resize the window to the given size.
  *
  * @param {number} width
  * @param {number} height
  *
  * @return None. This is an asynchronous call that sends all return information to the callback.
 */
 native function ResizeWindow();
 appshell.app.resizeWindow = function (width, height) {
     ResizeWindow(_dummyCallback, width, height);
 };

I also had a bit of an issue with the actual resize logic. You need to use the window handle of the browser->getHost()->getWindowHandle() parent:

`CefWindowHandle hWnd = getParent(browser->GetHost()->GetWindowHandle());

Answer 2

The ProcessMessageDelegate::OnProcessMessageReceived() method (appshell_extension.cpp) in which you try to debug the message name, is running in the Renderer process. You have to attach VS debugger to that subprocess to be able to debug it. Right now you are debugging the Browser process (main process).

For an easy way to debug subprocesses in console window, try creating a console window for each subprocess:

if (show_console) {
    AllocConsole();
    FILE* freopen_file;
    freopen_s(&freopen_file, "CONIN$", "rb", stdin);
    freopen_s(&freopen_file, "CONOUT$", "wb", stdout);
    freopen_s(&freopen_file, "CONOUT$", "wb", stderr);
}

Put this code before CefExecuteProcess() that launches subprocesses.

See how I've done it in the PHP Desktop project:

1. See the subprocess_show_console variable. https://code.google.com/p/phpdesktop/source/browse/phpdesktop-chrome/main.cpp?r=6de71bd0217a#126

2. A call to InitializeLogging() that runs the code above.

3. Then CefExecuteProcess is called.

---

On Linux it is easier to debug subprocesses in console window, as all the output from subprocesses is automatically forwarded to console from the main process. Windows is missing this neat feature.