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bsdiff/bspatch

bsdiff and bspatch are libraries for building and applying patches to binary files.

The original algorithm and implementation was developed by Colin Percival. The algorithm is detailed in his paper, Naïve Differences of Executable Code. For more information, visit his website at http://www.daemonology.net/bsdiff/.

I maintain this project separately from Colin's work, with the goal of making the core functionality easily embeddable in existing projects.

Contact

@MatthewEndsley
https://github.com/mendsley/bsdiff

License

This project is governed by the BSD 2-clause license. For details see the file titled LICENSE in the project root folder.

Overview

There are two separate libraries in the project, bsdiff and bspatch. Each are self contained in bsdiff.c and bspatch.c The easiest way to integrate is to simply copy the c file to your source folder and build it.

The overarching goal was to modify the original bsdiff/bspatch code from Colin and eliminate external dependencies and provide a simple interface to the core functionality.

I've exposed relevant functions via the _stream classes. The only external dependency not exposed is memcmp in bsdiff.

This library generates patches that are not compatible with the original bsdiff tool. The incompatibilities were motivated by the patching needs for the game AirMech https://www.carbongames.com and the following requirements:

Eliminate/minimize any seek operations when applying patches
Eliminate any required disk I/O and support embedded streams
Ability to easily embed the routines as a library instead of an external binary
Compile+run on all platforms we use to build the game (Windows, Linux, NaCl, OSX)

Compiling

The libraries should compile warning free in any moderately recent version of gcc. The project uses <stdint.h> which is technically a C99 file and not available in Microsoft Visual Studio. The easiest solution here is to use the msinttypes version of stdint.h from https://code.google.com/p/msinttypes/. The direct link for the lazy people is: https://msinttypes.googlecode.com/svn/trunk/stdint.h.

If your compiler does not provide an implementation of <stdint.h> you can remove the header from the bsdiff/bspatch files and provide your own typedefs for the following symbols: uint8_t, uint64_t and int64_t.

Examples

Each project has an optional main function that serves as an example for using the library. Simply defined BSDIFF_EXECUTABLE or BSPATCH_EXECUTABLE to enable building the standalone tools.

Reference

bsdiff

struct bsdiff_stream
{
	void* opaque;
	void* (*malloc)(size_t size);
	void  (*free)(void* ptr);
	int   (*write)(struct bsdiff_stream* stream,
				   const void* buffer, int size);
};

int bsdiff(const uint8_t* old, int64_t oldsize, const uint8_t* new,
           int64_t newsize, struct bsdiff_stream* stream);

In order to use bsdiff, you need to define functions for allocating memory and writing binary data. This behavior is controlled by the stream parameter passed to to bsdiff(...).

The opaque field is never read or modified from within the bsdiff function. The caller can use this field to store custom state data needed for the callback functions.

The malloc and free members should point to functions that behave like the standard malloc and free C functions.

The write function is called by bsdiff to write a block of binary data to the stream. The return value for write should be 0 on success and non-zero if the callback failed to write all data. In the default example, bzip2 is used to compress output data.

bsdiff returns 0 on success and -1 on failure.

bspatch

struct bspatch_stream
{
	void* opaque;
	int (*read)(const struct bspatch_stream* stream,
	            void* buffer, int length);
};

int bspatch(const uint8_t* old, int64_t oldsize, uint8_t* new,
            int64_t newsize, struct bspatch_stream* stream);

The bspatch function transforms the data for a file using data generated from bsdiff. The caller takes care of loading the old file and allocating space for new file data. The stream parameter controls the process for reading binary patch data.

The opaque field is never read or modified from within the bspatch function. The caller can use this field to store custom state data needed for the read function.

The read function is called by bspatch to read a block of binary data from the stream. The return value for read should be 0 on success and non-zero if the callback failed to read the requested amount of data. In the default example, bzip2 is used to decompress input data.

bspatch returns 0 on success and -1 on failure. On success, new contains the data for the patched file.