I've a client-server application on Mac. Client uploads a file and server downloads the file.
Sever reads a specific size of bytes from the client and write into the file. But in the middle user can delete the file using Finder context menu or from terminal. I want to stop any write/execution operation on this file from any other application till the download runs. It can be easily done using FILE_SHARE_READ while creating the file on Windows. But how we can achieve the same functionality on Mac?
I've tried advisory locks on Mac but no luck. If process A uses advisory locks on the file then process B can't access it but i can always delete the file using Finder context menu.
Are you sure you need to do this? So long as you've got an open file handle, it doesn't matter if the file is deleted, you can still read from it until you close the file handle. If the user deletes the file mid-transmission, it won't stop you from sending the full file.
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How can I make sure that a file uploaded through SFTP (in a Linux base system) stays locked during the transfer so an automated system will not read it?
Is there an option on the client side? Or server side?
SFTP protocol supports locking since version 5. See the specification.
You didn't specify, what SFTP server are you using. So I'm assuming the most widespread one, the OpenSSH. The OpenSSH supports SFTP version 3 only, so it does not support locking.
Anyway, even if your server supported file locking, most SFTP clients/libraries won't support SFTP version 5. Or even if they do, they won't support the locking feature. Note that the lock is explicit, the client has to request it.
There are some common workarounds for the problem:
As suggested by #user1717259, you can have the client upload a "done" file, once an upload finishes. Make your automated system wait for the "done" file to appear.
You can have a dedicated "upload" folder and have the client (atomically) move the uploaded file to a "done" folder. Make your automated system look to the "done" folder only.
Have a file naming convention for files being uploaded (".filepart") and have the client (atomically) rename the file after an upload to its final name. Make your automated system ignore the ".filepart" files.
See (my) article Locking files while uploading / Upload to temporary file name for example of implementing this approach.
Also, some SFTP servers have this functionality built-in. For example ProFTPD with its HiddenStores directive (courtesy of #fakedad).
A gross hack is to periodically check for file attributes (size and time) and consider the upload finished, if the attributes have not changed for some time interval.
You can also make use of the fact that some file formats have clear end-of-the-file marker (like XML or ZIP). So you know, when you download an incomplete file.
A typical way of solving this problem is to upload your real file, and then to upload an empty 'done.txt' file.
The automated system should wait for the appearance of the 'done' file before trying to read the real file.
A simple file locking mechanism for SFTP is to first upload a file to a directory (folder) where the read process isn't looking. You can "make" an alternate folder using the sftp> mkdir command. Upload the file to the alternate directory, instead of the ultimate destination directory. Once the SFTP> put command completes, then do a move like this:
SFTP> move alternate_path/filename destination_path/filename. Since the SFTP "move" is just switching the file pointers, it is atomic, so it is an effective lock.
My application is keeping watch on a set of folders where users can upload files. When a file upload is finished I have to apply a treatment, but I don't know how to detect that a file has not finish to upload.
Any way to detect if a file is not released yet by the FTP server?
There's no generic solution to this problem.
Some FTP servers lock the file being uploaded, preventing you from accessing it, while the file is still being uploaded. For example IIS FTP server does that. Most other FTP servers do not. See my answer at Prevent file from being accessed as it's being uploaded.
There are some common workarounds to the problem (originally posted in SFTP file lock mechanism, but relevant for the FTP too):
You can have the client upload a "done" file once the upload finishes. Make your automated system wait for the "done" file to appear.
You can have a dedicated "upload" folder and have the client (atomically) move the uploaded file to a "done" folder. Make your automated system look to the "done" folder only.
Have a file naming convention for files being uploaded (".filepart") and have the client (atomically) rename the file after upload to its final name. Make your automated system ignore the ".filepart" files.
See (my) article Locking files while uploading / Upload to temporary file name for an example of implementing this approach.
Also, some FTP servers have this functionality built-in. For example ProFTPD with its HiddenStores directive.
A gross hack is to periodically check for file attributes (size and time) and consider the upload finished, if the attributes have not changed for some time interval.
You can also make use of the fact that some file formats have clear end-of-the-file marker (like XML or ZIP). So you know, that the file is incomplete.
Some FTP servers allow you to configure a hook to be called, when an upload is finished. You can make use of that. For example ProFTPD has a mod_exec module (see the ExecOnCommand directive).
I use ftputil to implement this work-around:
connect to ftp server
list all files of the directory
call stat() on each file
wait N seconds
For each file: call stat() again. If result is different, then skip this file, since it was modified during the last seconds.
If stat() result is not different, then download the file.
This whole ftp-fetching is old and obsolete technology. I hope that the customer will use a modern http API the next time :-)
If you are reading files of particular extensions, then use WINSCP for File Transfer. It will create a temporary file with extension .filepart and it will turn to the actual file extension once it fully transfer the file.
I hope, it will help someone.
This is a classic problem with FTP transfers. The only mostly reliable method I've found is to send a file, then send a second short "marker" file just to tell the recipient the transfer of the first is complete. You can use a file naming convention and just check for existence of the second file.
You might get fancy and make the content of the second file a checksum of the first file. Then you could verify the first file. (You don't have the problem with the second file because you just wait until file size = checksum size).
And of course this only works if you can get the sender to send a second file.
How can I make sure that a file uploaded through SFTP (in a Linux base system) stays locked during the transfer so an automated system will not read it?
Is there an option on the client side? Or server side?
SFTP protocol supports locking since version 5. See the specification.
You didn't specify, what SFTP server are you using. So I'm assuming the most widespread one, the OpenSSH. The OpenSSH supports SFTP version 3 only, so it does not support locking.
Anyway, even if your server supported file locking, most SFTP clients/libraries won't support SFTP version 5. Or even if they do, they won't support the locking feature. Note that the lock is explicit, the client has to request it.
There are some common workarounds for the problem:
As suggested by #user1717259, you can have the client upload a "done" file, once an upload finishes. Make your automated system wait for the "done" file to appear.
You can have a dedicated "upload" folder and have the client (atomically) move the uploaded file to a "done" folder. Make your automated system look to the "done" folder only.
Have a file naming convention for files being uploaded (".filepart") and have the client (atomically) rename the file after an upload to its final name. Make your automated system ignore the ".filepart" files.
See (my) article Locking files while uploading / Upload to temporary file name for example of implementing this approach.
Also, some SFTP servers have this functionality built-in. For example ProFTPD with its HiddenStores directive (courtesy of #fakedad).
A gross hack is to periodically check for file attributes (size and time) and consider the upload finished, if the attributes have not changed for some time interval.
You can also make use of the fact that some file formats have clear end-of-the-file marker (like XML or ZIP). So you know, when you download an incomplete file.
A typical way of solving this problem is to upload your real file, and then to upload an empty 'done.txt' file.
The automated system should wait for the appearance of the 'done' file before trying to read the real file.
A simple file locking mechanism for SFTP is to first upload a file to a directory (folder) where the read process isn't looking. You can "make" an alternate folder using the sftp> mkdir command. Upload the file to the alternate directory, instead of the ultimate destination directory. Once the SFTP> put command completes, then do a move like this:
SFTP> move alternate_path/filename destination_path/filename. Since the SFTP "move" is just switching the file pointers, it is atomic, so it is an effective lock.
My .NET app updates a certain .xls file located in a shared folder inside the domain. Using VB.NET, how can I check if that file is being used by another user and unshare/close it, so my code can update the file properly?
NOTE:.Exe file(my app) will be executed in the server where shared folder is.
Windows and NTFS is designed to prevent this scenario. Unless you:
Get the Excel application which is holding the .xls file open to close it
Shut down the server's network connection assuming the Excel file is opened by client PCs - a highly undesirable step to take
Discover the PC on which the Excel.exe instance is running and use the Windows Taskkill command-line command to kill all Excel.exe instances (since you won't necessarily know which one has it open) on the machine - another undesirable step to take
Have a look at this answer, but this uses third-party utilities, and doesn't explain how these utilities do what they do though you may be able to Process.Start them.
you just can't get Windows/NTFS to release the file lock.
A possible alternative that I'm not sure will work with an xls (as opposed to an xls_) is to make the file shared, though this has some limitations.
I have an issue where occasionally I need to work at Starbucks.
When I upload a PHP file the connection is slow so if a user tries to access the PHP file while I am uploading it they will of course be issues a fatal error.
This is very inconvenient to my busy websites. Is there a way that when a file is uploaded it can be uploaded to a temporary location, and then the server moves it to the real location once finished?
You can make WinSCP upload the file to temporary file and rename it once transfer completes automatically.
In Preferences go to the Transfer > Endurance tab and select All Files in the Enable ... Transfer to temporary file name box.
For details refer to:
https://winscp.net/eng/docs/ui_pref_resume
Why don't you just upload the file to a temporary folder on the server and execute commands on the server to remove the old file and move the new file? It should move the file fast enough on the server to eliminate any hiccups the users would see unless their timing was just right.