Question

I am writing an “add-on” for Windows Picture viewer that will need to send commands to it (like “Show next/previous image”) and obtain file path to currently selected image. I managed to implement sending commands via SendMessage, but I don’t know how to request info from a process. Is this possible?
So far I can only extract filename from window title, but this restricts usage to just one folder, I need the full path.

[EDIT] I did some search and found, that there’s (undocumented?) possibility to find list of all handles used by process, using function NTQuerySystemInformation (As seen here Delphi – get what files are opened by an application).
The problem is, however, that the example provided there doesn’t show file handles for me at all (only non-harddrive device handles), and while I found working example here http://www.codeguru.com/Cpp/W-P/system/processesmodules/article.php/c2827/, seems like Picture Viewer doesn’t hold any handle to previewed file when launched from explorer.

Answer 1

You can get the Process “Current Directory” (as shown in Process Explorer).
Take a look at Two ways to get the command line of another process using Delphi by RRUZ.
Based on that article, we could get the CurrentDirectory found in the RTL_USER_PROCESS_PARAMETERS (offset 36) structure:

type
Uint4B = Cardinal;
Uint2B = Word;
UChar  = Byte;
Ptr32  = Pointer;

TUNICODE_STRING = UNICODE_STRING;
TCURDIR = packed record
  DosPath          : TUNICODE_STRING;
  Handle           : Ptr32;
end;

TRTL_USER_PROCESS_PARAMETERS = packed record
  MaximumLength    : Uint4B;
  Length           : Uint4B;
  Flags            : Uint4B;
  DebugFlags       : Uint4B;
  ConsoleHandle    : Ptr32;
  ConsoleFlags     : Uint4B;
  StandardInput    : Ptr32;
  StandardOutput   : Ptr32;
  StandardError    : Ptr32;
  CurrentDirectory : TCURDIR;
  DllPath          : TUNICODE_STRING;
  ImagePathName    : TUNICODE_STRING;
  CommandLine      : TUNICODE_STRING;
  Environment      : Ptr32;
  StartingX        : Uint4B;
  StartingY        : Uint4B;
  CountX           : Uint4B;
  CountY           : Uint4B;
  CountCharsX      : Uint4B;
  CountCharsY      : Uint4B;
  FillAttribute    : Uint4B;
  WindowFlags      : Uint4B;
  ShowWindowFlags  : Uint4B;
  WindowTitle      : TUNICODE_STRING;
  DesktopInfo      : TUNICODE_STRING;
  ShellInfo        : TUNICODE_STRING;
  RuntimeData      : TUNICODE_STRING;
  //   +0x090 CurrentDirectores : [32] _RTL_DRIVE_LETTER_CURDIR
end;

Here is how to obtain CurrentDirectory:

function GetCurrentDirectoryFromPid(PID: THandle): string;
const
  STATUS_SUCCESS             = $00000000;
  SE_DEBUG_NAME              = 'SeDebugPrivilege';
  OffsetProcessParametersx32 = $10; //16
  OffsetCurrentDirectoryx32  = $24; //36
var
  ProcessHandle        : THandle;
  rtlUserProcAddress   : Pointer;
  CurrentDirectory          : TCURDIR;
  CurrentDirectoryContents  : WideString;
  ProcessBasicInfo     : PROCESS_BASIC_INFORMATION;
  ReturnLength         : Cardinal;
  TokenHandle          : THandle;
  lpLuid               : TOKEN_PRIVILEGES;
  OldlpLuid            : TOKEN_PRIVILEGES;
begin
  Result:='';
  if OpenProcessToken(GetCurrentProcess(), TOKEN_ADJUST_PRIVILEGES or TOKEN_QUERY, TokenHandle) then
  begin
    try
      if not LookupPrivilegeValue(nil, SE_DEBUG_NAME, lpLuid.Privileges[0].Luid) then
        RaiseLastOSError
      else
      begin
        lpLuid.PrivilegeCount := 1;
        lpLuid.Privileges[0].Attributes  := SE_PRIVILEGE_ENABLED;
        ReturnLength := 0;
        OldlpLuid    := lpLuid;
        //Set the SeDebugPrivilege privilege
        if not AdjustTokenPrivileges(TokenHandle, False, lpLuid, SizeOf(OldlpLuid), OldlpLuid, ReturnLength) then RaiseLastOSError;
      end;

      ProcessHandle := OpenProcess(PROCESS_QUERY_INFORMATION or PROCESS_VM_READ, false, PID);
      if ProcessHandle=0 then RaiseLastOSError
      else
      try
        // get the PROCESS_BASIC_INFORMATION to access to the PEB Address
        if (NtQueryInformationProcess(ProcessHandle,0{=>ProcessBasicInformation},@ProcessBasicInfo, sizeof(ProcessBasicInfo), @ReturnLength)=STATUS_SUCCESS) and (ReturnLength=SizeOf(ProcessBasicInfo)) then
        begin
          //get the address of the RTL_USER_PROCESS_PARAMETERS struture
          if not ReadProcessMemory(ProcessHandle, Pointer(Longint(ProcessBasicInfo.PEBBaseAddress) + OffsetProcessParametersx32), @rtlUserProcAddress, sizeof(Pointer), ReturnLength) then
            RaiseLastOSError
          else
          if ReadProcessMemory(ProcessHandle, Pointer(Longint(rtlUserProcAddress) + OffsetCurrentDirectoryx32), @CurrentDirectory, sizeof(CurrentDirectory), ReturnLength) then
          begin
            SetLength(CurrentDirectoryContents, CurrentDirectory.DosPath.length);
            //get the CurrentDirectory field
            if ReadProcessMemory(ProcessHandle, CurrentDirectory.DosPath.Buffer, @CurrentDirectoryContents[1], CurrentDirectory.DosPath.Length, ReturnLength) then
             Result := WideCharLenToString(PWideChar(CurrentDirectoryContents), CurrentDirectory.DosPath.length div 2)
            else
            RaiseLastOSError;
          end;
        end
        else
        RaiseLastOSError;
      finally
        CloseHandle(ProcessHandle);
      end;
    finally
      CloseHandle(TokenHandle);
    end;
  end
  else
    RaiseLastOSError;
end;