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    1 zsync 0.6.2
    2 ===========
    4 zsync is a file transfer program. It allows you to download a file from a
    5 remote web server, where you have a copy of an older version of the file on
    6 your computer already. zsync downloads only the new parts of the file. It uses
    7 the same algorithm as rsync.
    9 zsync does not require any special server software or a shell account on the
   10 remote system (rsync, in comparison, requires that you have an rsh or ssh
   11 account, or that the remote system runs rsyncd). Instead, it uses a control
   12 file - a .zsync file - that describes the file to be downloaded and enables
   13 zsync to work out which blocks it needs. This file can be created by the admin
   14 of the web server hosting the download, and placed alongside the file to
   15 download - it is generated once, then any downloaders with zsync can use it.
   16 Alternatively, anyone can download the file, make a .zsync and provide it to
   17 other users (this is what I am doing for the moment).
   19 The zsync web site is at http://zsync.moria.org.uk/ . There are likely to be
   20 frequent releases, so check back often.
   22 Installation
   23 ------------
   25 See the file INSTALL for instructions on compiling and (optionally) installing
   26 zsync.
   28 As zsync is still at a very early stage, you may prefer not to install it, and
   29 to run the program where you compile it. It will work fine that way - it has no
   30 data files or libraries. The man(1) program on some systems will let you read
   31 the man pages without installing them, e.g. man -l doc/zsync.1 .
   33 zsync is free software. There is no implied support, no implied fitness for
   34 purpose, no warranty. You use it at your own risk.
   36 Use
   37 ---
   39 In its simplest form, as an end-user:
   41 zsync http://some.example.com/downloads/my-big-download.tar.zsync
   43 Someone has to make a .zsync file for the download before you can use zsync. As
   44 zsync has not been around long, there won't be many such downloads around :-).
   45 And you have to have an older copy of the file around, otherwise there is
   46 little point in using zsync - zsync normally looks in the current directory for
   47 a file of the same name as the one being downloaded (note: if the download is a
   48 .gz file, the local file should be uncompressed - use gzip -d to decompress it
   49 first). If the local file is not in the current directory or has a different
   50 name, you can specify it with -i, e.g.:
   52 zsync -i /var/lib/apt/lists/ftp.uk.debian.org_debian_dists_sarge_main_binary-i386_Packages http://zsync.moria.org.uk/s/sarge/Packages.zsync
   54 Offering zsync downloads
   55 ------------------------
   57 Simple example:
   58 Suppose you have http://example.com/dl/some-image-0.2.iso ; which is in
   59 /var/www/downloads/ on your server.
   61 cd /var/www/downloads/
   62 zsyncmake -u 'http://example.com/dl/some-image-0.2.iso' some-image-0.2.iso
   64 This creates some-image-0.2.iso.zsync in the same directory, and specifies the
   65 URL from which users can retrieve the full file. (Note that zsync requires both
   66 the public URL for the full download, and a local copy of the same file. Users
   67 will still need access to the full downloads - zsync merely allows then to save
   68 time by only downloading parts of the file.)
   70 A user with v0.1 of the same file can now use zsync to download only the new
   71 bits.
   73 zsync -i some-image-0.1.iso http://example.com/dl/some-image-0.2.iso.zsync
   75 Compressed example:
   76 Support you have http://example.com/downloads/big-0.2.tar.gz ; which is
   77 in /var/www/downloads/ on your server.
   79 cd /var/www/downloads/
   80 zsyncmake -u 'http://example.com/downloads/big-0.2.tar.gz' big-0.2.tar.gz
   82 This creates big-0.2.tar.zsync in the same directory, and specifies the URL
   83 from which users can see the file.  
   85 A user with v0.1 of the same file can now use zsync to download only the new
   86 bits:
   88 zsync -i <(zcat big-0.1.tar.gz) http://example.com/downloads/big-0.2.tar.zsync
   90 Feedback, Support
   91 -----------------
   93 Mail zsync-users@lists.sourceforge.net if you have questions about zsync. And
   94 join the mailing list if you are using it a lot or are interested in the
   95 ongoing development.
   97 Copyright, Author, Acknowledgements
   98 -----------------------------------
  100 zsync is based on the rsync algorithm, by Andrew Tridgell. It also incorporates
  101 a number of optimisations, based on ideas in academic papers by Utku Irmak,
  102 Svilen Mihaylov and Torsten Suel (primarily "Improved Single-Round Protocols
  103 for Remote File Synchronization", Sept 2004).
  105 zsync uses a large part of zlib - this code, in the zlib subdirectory, is
  106 copyright 1995-2003 Jean-loup Gailly and Mark Adler, see zlib/README for
  107 details. This code contains local changes by me that are not compatible with
  108 and not available in standard zlib; see zlib/README.zsync for an explanation.
  110 zsync includes an implementation of getaddrinfo by Motoyuki Kasahara. See
  111 getaddrinfo.c for the license, it's a BSD-style license; but normally zsync
  112 compiles against the getaddrinfo() in the system libc, so this code is not
  113 normally used.
  115 zsync also includes checksum code taken from OpenBSD. The MD4 code is public
  116 domain, by Colin Plumb and Todd C. Miller. The SHA1 code is also public
  117 domain, by Steve Reid. This code is in the libhash/ subdirectory, see the
  118 individual files for their non-copyright notices.
  120 The rest of the code (that is, everything not in the zlib and libhash
  121 subdirectories) is
  122 Copyright (C) 2004,2005,2007,2009 Colin Phipps <cph@moria.org.uk>.
  123 zsync is made available under the (clarified) Artistic License - see the file
  124 COPYING for details.
  126 Thanks also to:
  128 * Dennis Schridde, for contributing patches to improve portability.
  129 * Timothy Lee, for finding bugs and supplying patches.
  130 * Richard Kiss, for supplying a patch for MacOS X compilation.
  132 I must thank the developers above, whose code I have used. Also, I would like
  133 to thank the Free Software Foundation and its contributors, for gcc, gdb and
  134 emacs, the essential development tools. Also I would thank Sourceforge for
  135 providing the hosting facilities for the downloads and mailing list, and the
  136 compile farm for testing portability.
  138 Also, thanks to Érsek László, James Montgomerie, James Antill,
  139 saul@alien-science.org, Kent Mein, Marc Lehmann, Robert Lemmen, Mark Adler,
  140 Ricardo Correia, Karl Kalleberg, Michael Stone, Richard Lucassen, Duncan
  141 Mac-Vicar, Jari Aalto, Marcin Mirosław, Jan Varho and Loïc Minier for useful
  142 feedback and bug reports for previous versions.