07/Nov/2012

How to command the MultiStream ASIO Player remotely
---------------------------------------------------

// Hint: It's easy!


The controller application needs the following...


HWND hwDispatch = NULL;
COPYDATASTRUCT MyCDS;
char command[64]; // a buffer that gets the command from UI or a phone app or something



// Here are functions to validate commands before they are sent to the player

// Get filename extension and convert to lower case
char *FileExt2Lower(char *pFilename)
{
 char *ptr;
 char *pExt = strrchr(pFilename, '.');
 if(pExt != NULL)
 {
    // Convert extension to lower case...
    ptr = pExt + 1;
    while(*ptr != '\0')
    {
          *ptr = tolower(*ptr);
          ++ptr;
    }
 }
 return pExt;
}

bool isValidCommand(char *pCmd)
{
 if((*pCmd == '/') && (pCmd[1] == 'P'))return true;
 if((*pCmd == '/') && (pCmd[1] == 'R'))return true;
 if((*pCmd == '/') && (pCmd[1] == 'S'))return true;
 if((*pCmd == '/') && (pCmd[1] == '+'))return true;
 if((*pCmd == '/') && (pCmd[1] == '-'))return true;

 // Is it an /ADD command followed by a valid pathname?
 if((*pCmd == '/') && (pCmd[1] == 'A') && (pCmd[2] == 'D') && (pCmd[2] == 'D'))
 {
    // Is it a valid pathname?
    // First we'll check to see if it has a .wav, .mp3 or .m3u extension
    // Convert extension to lower case...
    char *pExt = FileExt2Lower(pCmd);
    if(pExt == NULL)
    {
       return false; // No extension!
    }
    if(!strcmp(pExt, ".wav"))
    {
       return true;
    }
    if(!strcmp(pExt, ".mp3"))
    {
       return true;
    }
    if(!strcmp(pExt, ".m3u"))
    {
       return true;
    }
 }
 return false;
}

// Note: The "/ADD pathname.ext" command allows you to add files to the play list.
// Obviously these files will only play if they already physically exist on the computer running MStream,
// but you could have a database of the pathnames of such files on the remote device,
// or you could even have an independent method of actually sending files to the computer
// before you add them to the play list.



To prepare to send messages to the player, do this...

 hwDispatch = FindWindowA(NULL, "MultiStream ASIO Player...");
 while(hwDispatch == NULL)
 {
       if(IDCANCEL == MessageBoxA(hApp, "Open the MultiStream ASIO Player, then click OK", "Controller", MB_OKCANCEL | MB_ICONSTOP))
       {
	  PostMessage(hApp, WM_CLOSE, 0, 0);
	  return;
       }
       hwDispatch = FindWindowA(NULL, "MultiStream ASIO Player...");
 }

 // Found MStream window: Handle now in hwDispatch;
 ZeroMemory(&MyCDS, sizeof(COPYDATASTRUCT));

// So later, you have a command from somewhere.
// Validate it and send if valid...
if(isValidCommand(command))
{
   MyCDS.lpData = command;
   MyCDS.cbData = strlen(command);
   SendMessage(hwDispatch, WM_COPYDATA, (WPARAM)(HWND)0,(LPARAM)(LPVOID)&MyCDS);
}




Meanwhile, in the MStream player Windows Message processing loop...
This is the actual code that processes remote commands sent to the MStream Player


LRESULT CMStreamDlg::WindowProc(UINT message, WPARAM wParam, LPARAM lParam) 
{
 switch (message)
 {
  ...
  ... 
  case WM_COPYDATA:

       if( ((COPYDATASTRUCT *)lParam)->cbData == 0)
       {
          return 0; // No data!
       }

       // Copy the command to our 256 char buffer...     
       strncpy(sCmdLine, (char *)((COPYDATASTRUCT *)lParam)->lpData, ( ((COPYDATASTRUCT *)lParam)->cbData > 255) ? 255 : ((COPYDATASTRUCT *)lParam)->cbData);

        // Ensure string is null-terminated...
       sCmdLine[( ((COPYDATASTRUCT *)lParam)->cbData > 255) ? 255 : ((COPYDATASTRUCT *)lParam)->cbData] = 0;

       if(*sCmdLine == '/')
       {

          // WM_COPYDATA found forward slash!

          char cmd = *(sCmdLine + 1);

          // It's a command! - maybe with garbage after the word?

          // Maybe "/PAUSE" or "/PLAY"?
          if(cmd == 'P')
          {
             OnBtnPlayPause(); // Toggle play/pause
          }else if(cmd == 'A') // It's /ADD to playlist, followed by a pathname
          {
             // Passing true to PlayCmdLineFile allows
             // it to simply add the files of the .m3u name passed
             // to current playlist, without disrupting what is there now
             // However, we need to pass a pointer to the filename that follows "/ADD "
             PlayCmdLineFile(true, &sCmdLine[5]);
          }else if(cmd == 'R') // Restart
          {
             OnBtnPrev();
          }else if(cmd == 'S') // Skip
          {
             OnBtnNext();
          }else if(cmd == '+') // vol up
          {
            int vol = m_SlidVolume.GetPos(); // Range = (0, 8);
            if(vol < 8)
            {
               ++vol;
               m_SlidVolume.SetPos(vol);
               pAudioStreams->SetGlobalAttenuation(8 - m_SlidVolume.GetPos());
            }
          }else if(cmd == '-') // vol down
          {
            int vol = m_SlidVolume.GetPos();
            if(vol > 0)
            {
               --vol;
               m_SlidVolume.SetPos(vol);
               pAudioStreams->SetGlobalAttenuation(8 - m_SlidVolume.GetPos());
            }
          }

       } // End if(*sCmdLine == '/')
       return 0;
 } // End switch (message)
}