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@@ -0,0 +1,180 @@ + -*- Text -*- + + Xdelta -- A binary delta generator + +Announcing version 1.1.2 of Xdelta. Xdelta is an application program +designed to compute changes between files. These changes (deltas) are +similar to the output of the "diff" program in that they may be used +to store and transmit only the changes between files. However, unlike +diff, the output of Xdelta is not expressed in a human-readable +format--Xdelta can also also apply these deltas to a copy of the +original file. Xdelta uses a fast, linear algorithm and performs well +on both binary and text files. + +Xdelta 1.1.2 is a stable, maintenence release. New, ongoing work on +Xdelta has focused on a new storage system with features similar to +the RCS command set. For more information on new development, see the +Xdelta-2.0 release series at http://xdelta.sourceforge.net. + +Xdelta was designed and implemented by Joshua MacDonald. The delta +algorithm is based on the Rsync algorithm, though implementation and +interface considerations leave the two programs quite distinct. The +Rsync algorithm is due to Andrew Tridgell and Paul Mackerras. + +To compile and install Xdelta, read the instructions in the INSTALL +file. Once you have done this, you should at least read the first few +sections of the documentation. It is available in info format. All +documentation is located in the doc/ subdirectory. + +This release, version 1.1.2, and future releases of Xdelta can be +found at http://xdelta.sourceforge.net. + +Xdelta is released under the GNU Library Public License (GPL), see the +file COPYING for details. + +There is mailing list for announcements: + + xdelta-announce@lists.sourceforge.net + +you can subscribe to the mailing list or file bug reports through +Sourceforge at: + + http://sourceforge.net/projects/xdelta/ + +Comments about Xdelta can be addressed to the following addresses: + + jmacd@cs.berkeley.edu + +The man page describes how to use Xdelta in more detail: + +NAME + xdelta - Invoke Xdelta + +SYNOPSIS + xdelta subcommand [ option... ] [ operand... ] + +DESCRIPTION + + Xdelta provides the ability to generate deltas between a pair + of files and later apply those deltas. It operates similar to + the diff and patch commands, but works on binary files and does + not produce a human readable output. + + Xdelta has three subcommands, delta, patch, and info. Delta + accepts two file versions and produces a delta, while patch + accepts the original file version and delta and produces the + second version. The info command prints useful information + about a delta. Each subcommand will be detailed seperately. + + Gzip processing + + Attempting to compute a delta between compressed input files + usually results in poor compression. This is because small + differences between the original contents causes changes in the + compression of whole blocks of data. To simplify things, + Xdelta implements a special case for gzip(1) compressed files. + If any version input to the delta command is recognized as + having gzip compression, it will be automatically decompressed + into a temporary location prior to comparison. This temporary + location is either the value of the TMPDIR environment + variable, if set, otherwise "/tmp". + + The Xdelta patch header contains a flag indicating that the + reconstructed version should be recompressed after applying + the patch. In general, this allows Xdelta to operate + transparently on gzip compressed inputs. + + There is one potential problem when automatically processing + gzip compressed files, which is that the recompressed content + does not always match byte-for-byte with the original + compressed content. The uncompressed content still matches, + but if there is an external integrity check such as + cryptographic signature verification, it may fail. To prevent + this from happening, the --pristine option disables automatic + gzip processing. + + MD5 integrity check + + By default, Xdelta always verifies the MD5 checksum of the + files it reconstructs. This prevents you from supplying an + incorrect input during patch, which would result in corrupt + output. Because of this feature, you can feel confident that + patch has produced valid results. The --noverify option + disables MD5 verification, but this is only recommended for + performance testing. + + Compressed patch format + + Xdelta uses a fairly simple encoding for its delta, then + applies zlib compression to the result. You should not have to + post-compress an Xdelta delta. + + Delta + + The delta subcommand has the following synopsis: + + xdelta delta [ option... ] fromfile tofile patchout + + Computes a delta from fromfile to tofile and writes it to patchout + + Patch + + The patch subcommand has the following synopsis: + + xdelta patch [ option... ] patchin [ fromfile [ tofile ]] + + Applies patchin to fromfile and produces a reconstructed + version of tofile. + + If fromfile was omitted, Xdelta attempts to use the original + fromfile name, which is stored in the delta. The from file + must be identical to the one used to create the delta. If its + length or MD5 checksum differs, patch will abort with an error + message. + + If tofile was omitted, Xdelta attempts to use the original + tofile name, which is also stored in the delta. If the + original tofile name already exists, a unique filename + extension will be added to avoid destroying any existing data. + + Info + The info subcommand has the following synopsis: + + xdelta info patchinfo + + Prints information about patchinfo and the version it + reconstructs, including file names, lengths, and MD5 checksums. + + Options + -0..9 Set the zlib compression level. Zero indicates no + compression. Nine indicates maximum compression. + + -h, --help + Print a short help message and exit. + + -q, --quiet + Quiet. Surpresses several warning messages. + + -v, --version + Print the Xdelta version number and exit. + + -V, --verbose + Verbose. Prints a bit of extra information. + + -n, --noverify + No verify. Turns off MD5 checksum verification of the + input and output files. + + -m=SIZE, --maxmem=SIZE + Set an upper bound on the size of an in-memory page + cache. For example, --maxmem=32M will use a 32 megabyte + page cache. + + -s=BLOCK_SIZE + Set the block size, unless it was hard coded (20% speed + improvement). Should be a power of 2. + + -p, --pristine + Disable the automatic decompression of gzipped + inputs, to prevent unexpected differences in the + re-compressed content. |