Question

When an application saves a file, a typical model is to save the file to a temporary location, then move the temporary file to the final location. In some cases that “move” becomes “replace”. In pseudo code:

Save temp file;
if final file exists
   delete final file;
move temp file to final filename;

There’s a window in there where the delete might succeed, but the move may not, so you can handle that by something like :

Save temp file;
if final file exists
   move final file to parking lot
move temp file to final filename;
if move succeeded       
   delete previous final file. 
else
   restore previous final file. 

Now to my questions:

1. is it preferred to save the temporary file to a temporary directory, and then move it, as opposed to saving the temporary file to the final directory? (if so, why?)

2. Is there a difference in attributes and permissions on a file that is first saved to a temp dir, then moved to the final file in a different directory, as compared to a file that is saved to a temp file in the final directory, and then renamed within the directory?

3. If the answers to both are YES, then how can I do the preferred thing while getting the appropriate ACL on file which was first saved to a temporary directory and then moved to a final directory?

Answer 1

Create a temp file in the temp folder if it is just a temporary file. Otherwise, create it in its final destination.

Caveats:

1) This may not work if the final destination is a ‘pickup’ folder (unless the ‘pickup’ process checks for locked files (which it should))

2) The final destination has special permissions that have to be created in code and applied before being able to move to the final destination.