zsyncmake - Online in the Cloud

PROGRAM:

NAME

zsyncmake - Build control file for zsync(1)

SYNTAX

zsyncmake [ { -z | -Z } ] [ -e ] [ -C ] [ -u url ] [ -U url ] [ -b blocksize ] [ -o
outfile ] [ -f targetfilename ] [ -v ] filename

zsync -V

DESCRIPTION

Constructs a metafile for the zsync client program to use to perform partial file
downloads. filename is the file that users wish to downloads; zsyncmake constructs the
appropriate metafile and writes filename.zsync in the current directory.

zsync will need at least one URL from which to download the file content. If the .zsync
will be in the same directory as the file to download, you can accept the default - zsync
includes a relative URL in the control file. If not, use the -u option to specify the URL.
You should also specify a URL for the uncompressed content with -U if available, as zsync
can make use of this for more efficient downloads sometimes. (You can edit the .zsync file
and add these afterwards - it has a simple key: value format in the header - but I suggest
you only do this once you are familiar with the tool.)

Note that zsyncmake itself does not (currently) verify the URLs or download any data, you
must provide the file data locally and check the URLs yourself.

OPTIONS

-b blocksize
Specify the blocksize to the underlying rsync algorithm. A smaller blocksize may be
more efficient for files where there are likely to be lots of small, scattered
changes between downloads; a larger blocksize is more efficient for files with
fewer or less scattered changes. This blocksize must be a power of two. If not
specified, zsyncmake chooses one which it thinks is best for this file (currently
either 2048 or 4096 depending on file size) - so normally tyou should not need to
override the default.

-C Tells zsyncmake not to generate any instructions in the .zsync telling the client
to compress the data it receives. This is implied by -z, but this option is here in
case you compress a file yourself only for the transfer, but want the client to end
up with the uncompressed file (e.g. you are transferring an ISO, which is held
compressed on the server, but which the client cannot use unless it is
uncompressed). Without -C, zsyncmake will produce directions for the client to
compress the file it receives where appropriate; -C is here so you can stop it
telling the client to do that.

-e Tells zsyncmake that the client must be able to receive the exact file that was
supplied. Without this option, zsyncmake only gives a weaker guarantee - that the
client will receive the data it contains (e.g. it might transfer the uncompressed
version of a .gz to the client). Note that this still doesn't guarantee that the
client will get it - the client could ignore the directives in the zsync file, or
might be incapable of exactly reproducing the compression used. But with -e you
know that zsyncmake has made it possible to get the exact data - it will exit with
an error if it cannot.

-f filename
Set the filename to include in the output file (this is what the file will be
called when a user finished downloading it).

-o outputfile
Override the default output file name.

-u url Specifies the URL from which users can download the content of the supplied file.
Users need the control file in order to find out what parts of the file they
already have, and they need the URLs to retrieve the parts of the file that they
don't already have. You can specify multiple URLs by specifying -u multiple times.
If not specified, zsync assumes that the file and the .zsync will reside in the
same public directory, and includes a single relative URL.

-U url Specifies a URL corresponding to the decompressed content of the file (only
applicable if it is a gzip file). zsync can sometimes download more efficiently
from the uncompressed data than from the compressed data - it will take advantage
of this if available. If no URLs are specifies, zsync looks for a file without the
.gz extension and assumes that this will be in the same public dir as the .zsync,
and includes a relative URL to it.

-v Enable verbose messages.

-V Prints the version of zsync.

-z Compress the file to transfer. Note that this overwrites any file called
filename.gz without warning (if you don't give a filename, e.g. because you are
reading from stdin, then zsync will use the name supplied with -f, or as a last
fallback, zsync-target.gz).

zsync can work with compressed data, and, in most cases where the data is not already
compressed, it is more efficient to compress it first. While you can just compress the
file to transfer with gzip, if you use this option then zsyncmake will compress the file
for you, producing a .gz file which is optimised for zsync. This can be 30% more efficient
at download time than compressing with gzip --best - but the compressed file will not be
as small at that produced by gzip.

-Z zsyncmake automatically looks inside gzip compressed files and exports the
underlying, uncompressed data to the zsyncmake file. In testing this has proved to
provide greater download efficiency. -Z overrides the default behaviour and treats
gzip files as just binary data. Use this if it is essential that the user receives
the compressed data (for instance because a cryptographic signature is available
only for the compressed data). zsync is typically no use if you specify -Z, unless
the gzip file was compressed with the special --rsync option to make it friendly to
differential transfers.

EXAMPLES

zsyncmake -C -u http://ftp.uk.debian.org/debian/dists/sarge/main/binary-i386/Packages.gz
Packages.gz

Note use of -C to save the client compressing the file on receipt; the Debian package
system uses the file uncompressed.

zsyncmake -z my-subversion-dump

In this case there is a large, compressible file to transfer. This creates a gzipped
version of the file (optimised for zsync), and a .zsync file. A URL is automatically added
assuming that the two files will be served from the same directory on the web server.

zsyncmake -e -u
http://www.mirrorservice.org/sites/ftp.freebsd.org/pub/FreeBSD/ports/distfiles/zsync-0.2.2.tar.gz
zsync-0.2.2.tar.gz

This creates a zsync referring to the named source tarball, which the client should
download from the given URL. This example is for downloading a source tarball for a
FreeBSD port, hence -e is specified so the client will be able to match its md5sum.

AUTHORS

Colin Phipps <[email protected]>

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