Open-VCDiff is a open source library from Google, which allows you to create and decode binary diffs. The library itself as well as the API are written in C++. For iPhone or Mac apps, where you typically download diffs using NSURLConnection or obtain them using other Objective-C APIs, this isn't terribly convenient.
This thin wrapper provides a pure Objective-C (not Objective-C++) interface for the decoder part. It allows you to specify the dictionary using an NSData object, the output as an NSFileHandle and feeding chunks of the diff as pure C byte buffers or NSData objects. There is also a helper for loading the dictionary from file. Internally, this memory-maps the file read-only as an NSData object. Memory mapping avoids holding the entire file in memory at once, which would be problematic on memory constrained systems, such as iOS devices.
The Pimpl idiom is used to keep any C++ out of the headers, so this is suitable to use with pure Objective-C apps. You will need to add libstdc++.dylib to your app's dependencies, however.
To use this code in an XCode project, download the Open-VCDiff source,
extract it, and run ./configure (but generally not make).
Add the 'src' directory, including the 'google'
subdirectory but excluding 'solaris' to a new target in your project (or a
sub-project), then add the source and header files from the src directory of this
repository. You'll want to omit all files ending in -test.cc, as well as
vcdiff_main.cc, which are needed only for the unit tests and the command line tool,
respectively. You will also want to add the path to the open-vcdiff 'src' directory
to the list of 'Search Headers' paths in your build target's settings. I've
added an example XCode project for building as a static library on iOS to the
objective-vcdiff-ios directory.
Your own code will only need to #import "VCDiffDecoder.h", none of the google stuff. About half of the open-vcdiff code is only used for encoding, so you can either remove those files manually or let the deadstripper deal with them automatically during the linking stage.
Open-VCDiff is subject to the Apache License 2.0, this wrapper is licensed under the more permissive 3-clause BSD license. (no attribution required)