# VPatch 2 ## Introduction VPatch allows to create a patch file to update previous versions of your software. The GenPat utitily generates the patch file. The plug-in can use the patch to update a file. Using a patch, you can reduce the download size of your updates, because only the differences between the files are included in the patch file. ## How to use ### Generate the patch file Make sure you have the source file (original version) and the target file (version to update to). For example, DATA.DTA (currently on user system) and DATA_20.DTA (version 2.0 of this data file). Now call the command line tool GenPat.exe:
    GENPAT data.dta data_20.dta data.pat
Now, the patch will be generated, this will take some time. Using the /B=(BlockSize) parameter of the GenPat utility (put it after the filenames), you can use a different block size. A smaller block size may result in a smaller patch, but the generation will take more time (the default blocksize is 64). ### Update the file during installation Use the VPatch plug-in to update a file using a patch file:
    vpatch::vpatchfile "pathfile.pat" "source.file" "new.file"
The result of the patch operating will be added to the stack and can be one of the following texts: OK OK, new version already installed An error occured while patching Patch data is invalid or corrupt No suitable patches were found Check example.nsi for an example. ### Multiple patches in one file GenPat appends a patch to the file you specified. If there is already a patch for the same orginal file in the patch file, the patch will be replaced. For example, if you want to be able to upgrade version 1 and 2 to version 3, you can put a 1 > 3 and 2 > 3 patch in one file. You can also put patches for different files in one patch file, for example, a patch from file A version 1 to file A version 2 and a patch from file B version 1 to file B version 2. Just call the plug-in multiple times with the same patch file. It will automatically select the right patch (based on the file CRC). ### GenPat exit codes In version 2.1 support was added for exit codes (known as error levels in the DOS period) to GenPat. GenPat will return an exit code based on succes of the patch generation. Here is a list of the possible exit codes:
Exit code | Description
0 | Success
1 | Arguments missing
2 | Source file not found
3 | Target file not found
4 | Unknown error while reading existing patch file
5 | Unknown error while generating patch
6 | Unknown error while writing patch file to disk
10 | CRC of source and target file are equal
11 | Not enough memory for source file
12 | Not enough memory for target file
These exit codes can be useful when you generate patch files through a script. ## Source code ### NSIS plug-in (C++) The source of the NSIS plug-in that applies patches can be found in the Source\Plugin folder. ### Patch Generator (Delphi) The most interesting part of VPatch, the actual patch generation algoritm, can be found in Source\GenPat\PatchGenerator.pas. The header of that file contains a brief explanation of the algoritm as well. ### User interface (Delphi) A user interface is included as well, which you will have to build yourself because the GUI executable was too large to include. Besides Borland Delphi 6 or higher (you can use the freely available Personal edition), you will also need to install the VirtualTreeView component by Mike Lischke. ## Version history 2.1 Added argument checking and error handling to GenPat. Now returns exit codes as well to indicate success/failure (and the reason for failure). Only GenPat has changed in this version compared to 2.0 final. Bug Fix: GenPat no longer gives an Access Violation when attempting to patch a file smaller than 64 bytes into a file larger than 64 bytes. 2.0 final Cleaned up source code for the patch generator, which is now included (this code is written in Borland Delphi 6 and compiles with the freely available Personal edition). 2.0 beta 2 All new algorithm used in the patch generator: much faster (up to 90%) while using smaller block sizes (higher compression) Created a NSIS 2 plugin Works with small files Replaces existing patch in file if original file CRC is identical ## Credits Written by Koen van de Sande C plug-in by Edgewize New documentation and example by Joost Verburg ## License
    Copyright (C) 2001-2003 Koen van de Sande

    This software is provided 'as-is', without any express or implied
    warranty. In no event will the authors be held liable for any damages
    arising from the use of this software.

    Permission is granted to anyone to use this software for any purpose,
    including commercial applications, and to alter it and redistribute
    it freely, subject to the following restrictions:

    1. The origin of this software must not be misrepresented;
       you must not claim that you wrote the original software.
       If you use this software in a product, an acknowledgment in the
       product documentation would be appreciated but is not required.
    2. Altered versions must be plainly marked as such,
       and must not be misrepresented as being the original software.
    3. This notice may not be removed or altered from any distribution.