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Spying a file system

By , 22 Sep 2003
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Introduction

Windows applications can do dynamic monitoring of any specified directory. Once changes have occurred and are detected, the spy application can run various tasks ( run antivirus, log activity, determine more information about changes, call other tasks etc).

Win 32 API provides three functions that are based on the events:

  • FindFirstChangeNotification
  • FindNextChangeNotification
  • FindCloseChangeNotification
  • ReadDirectoryChangesW

These allow creating watchdog or spying applications.

How to create

First of all spy application should call FindFirstChangeNotification to create event handler to monitor changes specified as the functions parameters.

HANDLE h = FindFirtsChangeNotification("C:\\Program Files”, TRUE, mask); 

This function allows to handle following types of notifications:

  • FILE_NOTIFY_CHANGE_FILE_NAME – File creating, deleting and file name changing

  • FILE_NOTIFY_CHANGE_DIR_NAME – Directories creating, deleting and file name changing

  • FILE_NOTIFY_CHANGE_ATTRIBUTES – File or Directory attributes changing

  • FILE_NOTIFY_CHANGE_SIZE – File size changing

  • FILE_NOTIFY_CHANGE_LAST_WRITE – Changing time of write of the files

  • FILE_NOTIFY_CHANGE_SECURITY – Changing in security descriptors

The result of FindFirstChangeNotification can be passed as parameter in to WaitForSingleObject and when specified event has occurred, application can do various actions such as: antivirus starting, adding record to the log file, and so on. Note that this function does not detect changes, it only creates synchronization event and marks it if changes are made. After our spy application handles changes, it should call FindNextChangeNotification to continue monitoring or FindCloseChangeNotification to finish it.

Win32 API provides also ReadDirectoryChangesW that can operate with following filters (MSDN) :

FILE_NOTIFY_CHANGE_FILE_NAME

Any file name change in the watched directory or subtree causes a change notification wait operation to return. Changes include renaming, creating, or deleting a file.

FILE_NOTIFY_CHANGE_DIR_NAME

Any directory-name change in the watched directory or subtree causes a change notification wait operation to return. Changes include creating or deleting a directory.

FILE_NOTIFY_CHANGE_ATTRIBUTES

Any attribute change in the watched directory or subtree causes a change notification wait operation to return.

FILE_NOTIFY_CHANGE_SIZE

Any file-size change in the watched directory or subtree causes a change notification wait operation to return. The operating system detects a change in file size only when the file is written to the disk. For operating systems that use extensive caching, detection occurs only when the cache is sufficiently flushed.

FILE_NOTIFY_CHANGE_LAST_WRITE

Any change to the last write-time of files in the watched directory or subtree causes a change notification wait operation to return. The operating system detects a change to the last write-time only when the file is written to the disk. For operating systems that use extensive caching, detection occurs only when the cache is sufficiently flushed.

FILE_NOTIFY_CHANGE_LAST_ACCESS

Any change to the last access time of files in the watched directory or subtree causes a change notification wait operation to return.

FILE_NOTIFY_CHANGE_CREATION

Any change to the creation time of files in the watched directory or subtree causes a change notification wait operation to return.

FILE_NOTIFY_CHANGE_SECURITY

Any security-descriptor change in the watched directory or subtree causes a change notification wait operation to return.

Sample

Give your attention to the following code in the demo project:

void ThreadRoute( void* arg )
{
 HANDLE file = FindFirstChangeNotification("c:\\Program Files", 
     FALSE, (DWORD)((Param*)arg)->parameter);
 WaitForSingleObject(file, INFINITE);
 CTime tm = CTime::GetCurrentTime();
 m_Sec.Lock(); // Enter to Critical section for display notification
 int item = pList->InsertItem(pList->GetItemCount(), ((Param*)arg)->message);
 pList->SetItemText(item, 1, tm.Format("%Y/%m/%d - %H:%M:%S"));
 m_Sec.Unlock();

 while (true)
 {
   FindNextChangeNotification(file);
   WaitForSingleObject(file, INFINITE);
   tm = CTime::GetCurrentTime();
   m_Sec.Lock(); // Enter to Critical section for display notification
   item = pList->InsertItem(pList->GetItemCount(), ((Param*)arg)->message);
   pList->SetItemText(item, 1, tm.Format("%Y/%m/%d/ - %H:%M:%S"));
   m_Sec.Unlock();
  }
}

and here is the fragment using ReadDirectoryChangesW

void ThreadRoute1( void* arg ) 
 {
  USES_CONVERSION;
  HANDLE hDir = CreateFile( 
    CString("c:\\Program Files"), /* pointer to the file name */
    FILE_LIST_DIRECTORY,                /* access (read-write) mode */
    FILE_SHARE_READ|FILE_SHARE_DELETE,  /* share mode */
    NULL, /* security descriptor */
    OPEN_EXISTING, /* how to create */
    FILE_FLAG_BACKUP_SEMANTICS, /* file attributes */
    NULL /* file with attributes to copy */
  );

  FILE_NOTIFY_INFORMATION Buffer[1024];
  DWORD BytesReturned;
  while( ReadDirectoryChangesW(
     hDir, /* handle to directory */
     &Buffer, /* read results buffer */
     sizeof(Buffer), /* length of buffer */
     TRUE, /* monitoring option */
     FILE_NOTIFY_CHANGE_SECURITY|
     FILE_NOTIFY_CHANGE_CREATION|
     FILE_NOTIFY_CHANGE_LAST_ACCESS|
     FILE_NOTIFY_CHANGE_LAST_WRITE|
     FILE_NOTIFY_CHANGE_SIZE|
     FILE_NOTIFY_CHANGE_ATTRIBUTES|
     FILE_NOTIFY_CHANGE_DIR_NAME|
     FILE_NOTIFY_CHANGE_FILE_NAME, /* filter conditions */
     &BytesReturned, /* bytes returned */
     NULL, /* overlapped buffer */
     NULL))... /* completion routine */

These are thread functions that do the described spying actions.

Conclusion

The attached Demo application starts separate threads to monitor all possible changes in the "c:\\Program Files" directory and shows occurred notifications and its date/time in the List control. Demo application shows also how to use ReadDirectoryChangesW and compare both methods visually.

Functionality of the Demo application can be extended to determine concrete changes, to log changes in to file, run external applications or tasks on the specified event, use described methods as system service and so on. Readers have full freedom to modify and use the demo project.

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

About the Author

Vitali Halershtein
Software Developer (Senior)
Belarus Belarus
I am a professional Software Developer with more than 10 years' experience.
Certifications: MCSD, MCP, Brainbench, Masters Degree in Computer Science.
 
I am open for contacts and interesting ideas.
You can write me at:
vitali_eh@yahoo.com

Comments and Discussions

 
GeneralMy vote of 5 PinmemberXinDavid13-Jun-12 20:54 
GeneralThanks Pinmemberpeterpc070116-Mar-12 15:46 
GeneralMy vote of 5 PinmemberMember 80364465-Nov-11 5:59 
GeneralMy vote of 4 Pinmembersahar792516-Jan-11 4:38 
GeneralMy vote of 5 PinmemberOption Greek22-Sep-10 3:26 
GeneralIt is a good example for ReadDirectoryChangesW Pinmemberzz96227-Oct-09 23:14 
GeneralRe: It is a good example for ReadDirectoryChangesW Pinmemberconrad Braam2-Sep-10 4:10 
Actually no, I disagree on one count only.
 
The example is good, but fails to take into account that the buffer returned is populated with an array of changes. not just one - the code does not show iterating over the list of objects.
 
If there are no objections I will paste just the code changes in here:
 
FILE_NOTIFY_INFORMATION *pRecord = Buffer;
do
{
switch(pRecord->Action)
{
case FILE_ACTION_ADDED: helper_txt = "The file was added to the directory"; break;
case FILE_ACTION_REMOVED: helper_txt = "The file was removed from the directory"; break;
case FILE_ACTION_MODIFIED: helper_txt = "The file was modified. This can be a change in the time stamp or attributes."; break;
case FILE_ACTION_RENAMED_OLD_NAME: helper_txt = "The file was renamed and this is the old name."; break;
case FILE_ACTION_RENAMED_NEW_NAME: helper_txt = "The file was renamed and this is the new name."; break;
}

m_Sec.Lock();
int item = pList1->InsertItem(pList1->GetItemCount(), CString(pRecord->FileName).Left(pRecord->FileNameLength / 2) + " - " + helper_txt );
pList1->SetItemText(item, 1, tm.Format("%Y/%m/%d/ - %H:%M:%S"));
m_Sec.Unlock();

if (0== pRecord->NextEntryOffset)
break;
// point to next record in array
pRecord = (FILE_NOTIFY_INFORMATION *)(&((unsigned char*)Buffer)[pRecord->NextEntryOffset]);
} while (TRUE);

 
I have however found that the watchers seem to be locking changes on the actual directory opened. I found the case for this, is in the way the directory is opened before watching - will prevent anyone from adding folders or files, simple to fix: add
FILE_SHARE_WRITE
to the open flags when opening the directory handle Smile | :)
Enjoy
Conrad -
The world waits for you to stick your neck out, it's not easy. But once you actually stand up, you do get noticed.
http://www.plcsimulator.org/

QuestionGet new path Pinmemberfer_cyberlinklabs3-Mar-09 14:55 
AnswerRe: Get new path PinmemberKdiggins14-Mar-09 7:21 
GeneralHelp - Cannot compile on VS 2009 - link error PinmemberJohn Denney15-Aug-08 23:04 
GeneralRe: Help - Cannot compile on VS 2009 - link error PinmemberJohn Denney21-Aug-08 1:49 
GeneralReadDirectoryChangesW Problem~~ Pinmemberyork52812-Jun-08 8:09 
GeneralRe: ReadDirectoryChangesW Problem~~ Pinmemberconrad Braam2-Sep-10 4:12 
GeneralFILE_ACTION_RENAMED_NEW ASSERT FAILURE Pinmemberphoenix_fei_fei18-Nov-07 13:40 
GeneralDo not detect all the changed files PinmemberGameProfessor10-May-07 16:55 
GeneralRe: Do not detect all the changed files PinmvpDavidCrow4-Oct-07 7:43 
GeneralRe: Do not detect all the changed files PinmemberArsene Shahin2-Jun-08 23:51 
QuestionRe: Do not detect all the changed files PinmvpDavidCrow3-Jun-08 4:20 
GeneralRe: Do not detect all the changed files PinmemberVitali Halershtein3-Jun-08 4:14 
GeneralRe: Do not detect all the changed files PinmvpDavidCrow3-Jun-08 4:22 
GeneralRe: Do not detect all the changed files PinmemberVitali Halershtein3-Jun-08 4:39 
QuestionHow to terminate the thread? PinmemberGuna Velu1-May-07 23:23 
AnswerRe: How to terminate the thread? PinmvpDavidCrow4-Oct-07 7:45 
AnswerRe: How to terminate the thread? PinmemberVitali Halershtein20-Dec-07 0:24 
Questionlocking a folder and particular drive Pinmemberamitkumart13-Apr-07 20:31 

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