I would like to generate some temporary files in the course of my application. Specifically, I'm using AVAudioRecorder to record a file that I, upon stopping the recording, would like to load and edit/process. My question is:
What is the appropriate standard place to create temporary files. Is there some generally accepted approach to this for Mac or for iPad programming in general? I don't want to simply create a directory and write files into it if there is a proper protocol to this.
The answer to this question is actually a lot more complicated then one might assume. One cannot necessarily just use NSTemporaryDirectory and be done. I cocoadev.com has some good pages on this topic and I would suggest that you study them yourself and determine what will work best for your circumstance.
http://www.cocoadev.com/index.pl?NSTemporaryDirectory
http://www.cocoadev.com/index.pl?GettingTemporaryFolderOnSpecificVolume
The usual place for applications to store temporary data is /var/tmp. You could also use /tmp but this directory is for system-generated temporary files and anything in /tmp is deleted when the machine reboots.
What I found was that according to the iOS Application Programming Guide, I am supposed to query for the appropriate temporary folder for my application via NSTemporaryDirectory(). I tried this and it returned a folder within the /var directory, in my case '/var/folders/pQ/pQ+ZqZCSHWSIHftcbIo57U+++TI/-Tmp-/'.
/tmp or /usr/tmp are the usual places to store temporary files in Unix (which Mac OS X and iOS are).
Related
Although we don't need it much but still if we want to know the original file, how would we do that?
How can we find the original file in case we create several hard links to a file?
I assume that you are talking about hard links in a POSIX file system.
You can't. As far as the file system is concerned, the hard links are indistinguishable.
OK. Maybe if you created the hard links via a shell, the commands might be in the shell history. Or the information might be in log files. Or possibly audit files ... if auditing is enabled. But not normally.
For the purposes of a security test involving Windows servers, I would like to attempt uploading a Symbolic link to a Windows web application. However, based on the information officially available, it is unclear whether Windows hard links (Which I suppose are the same as NTFS junctions) exist as a file that can be copied from the hard disk the same way it does on Linux. It's vague, but I get the sense that NTFS junctions are some other kind of file system artifacts which is different than "regular" files - I can't find the documentation to confirm or deny this. I.E NTFS I want to know if NTFS supports the direct manipulation of the symlink record such that I could move the symlink to a different computer.
I am aware that Windows softlink files (.lnk) are not limited in this way, but they do not suit the purposes of the test.
My Aim is to copy a symlink off of a virtual machine, and then upload it to the server which I am testing.
Is this possible? (I am under the impression it is not.) From what I have seen absolutely every program on Windows would regard the hardlink as the destination file. Is there a way around this, perhaps by using a special editor to temporarily corrupt the file? If the symlink exists as a normal file on the file system can the symlink be altered so it can moved to a non-Windows OS for further use?
Let me know if this would be a better question for server fault. Since this is not directly about security, and is more of mundane technical problem in the service of a security exercise, I don't think it would fit on Stack Exchange security.
It's hard to provide a very direct answer. I work on a backup/repair/imaging project, and I copy whole disk images to a server via a web service - so, it's possible to do what you want, but there's a lot to consider.
Hardlinks
It is generally assumed that hardlinks cannot be distinguished from each other, however, there is a subtle difference between linked files and their "original" file. That difference is that queries to the $MFT (using USN-related arguments on the winapi function DeviceIOControl) will only return one of the files. This may be considered the original file. You can then call the winapi function NtQueryInformationFile to enumerate the hard links.
Symlinks and junctions are different animals...
You can know that a folder is a junction or a symlink, by getting the attributes from it. There's a ReparsePoint flag in the attributes if it's a junction or a symlink. BTW - the difference between junctions and symlinks is that the junction is a redirect to another location on the same volume, while a symlink is a redirect to an off-volume location. The redirect target is always another folder either way.
What's interesting is that both symlinks and junctions look and act like folders, while they are really files containing redirect information. When you open 'em, NTFS will normally look at the redirect, and open the redirect target. NTFS checks the permissions at the redirect target, so as an attack, this might not be a robust strategy.
When opening a junction/symlink, you can add a flag FILE_FLAG_OPEN_REPARSE_POINT. When you do this, NTFS does not perform the redirect, but opens the content, which is actually redirect information, and assuming you know the format of that information, it is possible to reconstruct the junction/symlink at the server. Note that the redirect may point to a location that may not exist, or may exist only temporarily. This is expected as some network resources may not always be available.
So, in short, it's possible to copy a junction or a symlink...while copying a hard link nominally means copying the file...with the foregoing subtleties in mind. You can create a hard link manually, too, as long as the target file exists.
With hardlinks, there's one interesting kink in the NTFS security picture. If a user has access to a file, and you create a hardlink to that file in a folder the user doesn't have access to, the user can still open that file using the path to the hard link. This is because the link and the original file are both pointing to the same file (and security info) on disk. Permissions changed on any of the links affect all the links. Without knowing this, you can inadvertently wreak havoc on a file system :-)
I know this is a bit helter-skelter, so let me summarize this way:
NTFS directory entries can be folders or files. Hardlinks are directory entries that all point to one file. Symlinks and junctions are really files that act like folders for most practical purposes (until you know how to get at the redirect info as described above).
AFAIR, NTFS (directory) junctions are actually symbolic links. The juctnion is implemented as a special file attribute called repars point that contains the link target.
Hardlinks, on the other hand, are implemented as direct references to the base MFT record of the target file and are stored as regular entries inside directory tree. You actually cannot distinguish a hardlink from the "original" file (every file and directory actually has at least one hardlink since it is contained somewhere within the directory tree).
If you wish to copy a symbolic link itself, you need to know that it is a symbolic link and extract the information about its target. File operations (except deletion and, probably, renamng) are redirected to the link target. So, you can, in general, copy a symbolic link by creating its exact copy in the destination area.
The actual question is, whether the interface you are using to perform the copy operation allows you to create symbolic links on the target.
Is it possible to append/remove a ressource file to a binary at execution time?
I have an application written with go, which saves/searches data from a database file, and i would like this database file to be embedded to the binary, and updated by the application itself.
This way the application would be self contained with its database.
Modifying the executable, this is generally a very bad idea.
Several issues pop right into my head, such as:
Does the current user have sufficient permissions?
Is the file locked during execution?
What about multiple running instances of the application?
Even if you manage to do just that, think of what anti-virus and firewall applications will say to it: most when they detect the change will flag the executable and/or contain it, or deny running it, or some may even delete it. Rightfully, as this is what many viruses do: modify existing executables.
Also virus scanner databases maintain reports where files (their contents) are identified based on the hash of their content. Modifying the executable will naturally change the file content hash, thus render the file unknown / suspicious to these databases.
As mentioned, just write / cache data in separate file(s), preferably in user's home folder or in the application folder (next to the executable, optionally in sub-folders). Or make the cache file / folder a changeable option (command line flags).
Technically, this is possible, but this is a bad idea. Your application could be run by users not having write permissions to your binary.
If you're talking about a portable app, your best option might be using a file in the same directory the binary is located, otherwise - use the user's home directory according to the conventions of the OS you're running on. You can use the os/user package to find the home directory.
I have a large shared drive (~500Gb, 20k files, samba/afs). I would like to add all the files in there to a perforce repository.
I imagine adding/committing them all in one fell swoop is not a good idea.
How would I then to do that? Add/commit one by one? And would that ensure that the files on the shared drive are NOT locked?
I am comfortable with bash or perl, and this would have to happen under Mac OS X.
Bonus question: would the method also allow checking in the same files if they get changed on the shared drive via a cron job?
Thanks.
It will depend on your hardware what Perforce can handle. You should not likely have to add the files one at a time, however. This article here shows how to add whole directories at once:
Regarding your bonus question, yes you can easily handle files modified by your cron job by using the reconcile method. See the section 'Reconcile through the Command Line' in this article.
What I need is a directory which the user can handle as a single file in the Windows explorer. Does something like this exist? If not, what comes closest?
The closest thing is probably Alternate Data Streams, although those are more akin to MacOS Named Forks than Bundles.
There are also some special cases, for example if you save a website with Internet Explorer you get an HTML file and a folder which are linked together.
Depends on your particular needs. As mentioned above, named streams are possible (on NTFS), however you should notice that not all applications copy files with named streams correctly. In some scenarios regular ZIP archives can work (Explorer shows them as folders). If you are doing software development, there exist libraries that let you store many files in one container file (eg. SolFS).
I think you can create a folder with an extension, e.g. Myfolder.bundle, then you can associate that extension with a custom icon. So it looks like a bundle as far as the end user is concerned.