Overview
Whenever iTunes syncs with an iPhone, it creates a backup of the files on the device. This backup is stored in:
~/Library/Application Support/MobileSync/Backup
It can be interesting to look at these backups, but a bit of work is necessary to get access to them. I've whipped up a quick and dirty application to display the most common cases, iPhone Backup Slurper.
mdbackup Files
The files themselves are named with what appears to be a hex representation of a UUID with the extension "mdbackup". One of these files corresponds to a single filesytem entry on the iPhone. The file is just a standard plist, with binary encoding. You can convert this to a text file using
plutil -convert <src path> -o <dest path>
The plist contains the following keys:
- Domain: The scope of the file. Options are "HomeDomain", "LibraryDomain", or a specific application bundleID.
- Path: The path within the domain where the file is stored on the iPhone.
- Data: The contents of the file. I assume that this is data-fork only, if the iPhone supports multiple forks.
The file can be any arbitrary kind of file, but in practice, there are only a few different types of files that developers seem to actually be saving in the filesystem.
The app reads in the plist, displays the metadata keys described above, and does some heuristics on the data to try to guess how to display it. The most common cases I found by browsing my own backup directory were:
- text file
- plist saved as a string file
- binary plist
- image
- zip file
- sqlite 3 database
- completion dictionary
iPhone Backup Slurper will print any of these out to a descriptive file when it encounters them. If the backup contains an image, it will display the image. For a zip file, it will display the filenames embedded in the zip. It will dump the contents of an SQLite database.
There are two pathological cases I found while playing with this that I couldn't figure out how to handle. First, there are some files that appear to be SQLite 3 databases – the file begins with the string "SQLite format 3". But the version of SQLite 3 included with Leopard 10.5.5 gawks when trying to read them.
Second are the audio files bundled with Tap Tap Revolution. The Quicktime APIs don't recognize them as valid m4a files. Maybe they're actually something different.
Manifest Files
The backup directory also contains a plist named "Manifest.plist". This is a manifest of all of the mdbackup files in the same directory. iPhone Backup Slurper can also display the contents of this file by choosing Open Manifest from the File menu.
The manifest contains the following key/value pairs:
- AuthVersion: The current version of this file.
- AuthData: The string "Forty Two" encoded as hex without a null terminator.
- AuthSignature: The SHA1 signature of the "Data" key.
- Data: The actual manifest stored as a binary plist.
- Applications: A list of each application, keyed by the applications' bundle identifiers.
- DeviceId: The device that this manifest is intended to be used with.
- Files: A list of each of the files in the backup directory, keyed by the file's UUID. Each entry contains filesystem attributes for the file and a DataHash to ensure data integrity. I don't know the hash algorithm used by the data hash, but I suspect it's something tricky that uses the "Forty Two" value mentioned above as a hash seed.
Conclusion
I hope iPhone Backup Slurper is useful to people or just fun for exploration! If nothing else, it's a good example of using a bunch of different APIs to parse different filetypes. Finally, I'm indebted to OmniGroup for their useful OSLDatabaseController sqlite wrapper class.
