=head1 NAME

nbdkit-torrent-plugin - serve a BitTorrent file or magnet link over NBD

=head1 SYNOPSIS

 nbdkit torrent FILE.torrent|'magnet:?xt=urn:...'
                [file=DISK.iso] [cache=DIR] ...

=head1 DESCRIPTION

C<nbdkit-torrent-plugin> is an L<nbdkit(1)> plugin which lets you
serve a single file from within a torrent read-only over NBD.  The
torrent to download can be a local F<FILE.torrent> file, or a L<magnet
link|https://en.wikipedia.org/wiki/Magnet_URI_scheme>.

A single torrent contains a collection of files, and by default this
plugin serves the largest file within the torrent.  For operating
system installers this is usually the large ISO file and ignores other
small files like READMEs.  You can also select a particular file by
name to serve.

If you want to turn a file hosted on a web server into an NBD export
use L<nbdkit-curl-plugin(1)> instead.  If you have a local ISO you can
simply serve it using L<nbdkit-file-plugin(1)>.  If you want to turn a
local directory into an ISO use L<nbdkit-iso-plugin(1)>.

=head1 NOTES

This plugin implements a full-featured BitTorrent client.  BitTorrent
clients form a peer-to-peer (p2p) network and upload the file to other
clients as well as downloading.

By default the plugin will cache the downloaded torrent into
C<$TMPDIR>, potentially consuming a lot of disk space.  See the
C<cache=DIR> parameter for how to control this.

By default the plugin will consume all available network bandwidth in
both download and upload directions.  To limit it, set
C<download-rate-limit> and C<upload-rate-limit> appropriately.

=head1 EXAMPLES

=head2 Boot the Fedora installer

Choose the right URL from L<https://torrent.fedoraproject.org/>:

 url=https://torrent.fedoraproject.org/torrents/Fedora-Server-dvd-x86_64-32.torrent
 wget $url
 nbdkit torrent Fedora-Server-*.torrent \
        --run 'qemu-system-x86_64 -m 2048 -cdrom "$uri" -boot d'

=head2 Boot the Debian installer

Choose the right URL from L<https://www.debian.org/CD/torrent-cd/>:

 url=https://cdimage.debian.org/debian-cd/current/amd64/bt-dvd/debian-10.4.0-amd64-DVD-1.iso.torrent
 wget $url
 nbdkit torrent debian-*.torrent \
        --run 'qemu-system-x86_64 -m 2048 -cdrom "$uri" -boot d'

=head1 PARAMETERS

=over 4

=item B<cache=>DIR

Set a directory which will be used to store the partially downloaded
torrent between runs.

This parameter is optional.  If I<not> given then the plugin will
create a randomly named temporary directory under C<$TMPDIR>, and will
attempt to ensure it is cleaned up on exit (thus unless you set
C<cache>, no state is saved between runs and the whole torrent must be
downloaded each time).

=item B<connections-limit=>N

Set limit on number of connections to other peers that this client
will open (default 200).

=item B<download-rate-limit=>BITS_PER_SEC

Set the download rate limit in bits per second.  Usual abbreviations
can be used such as C<download-rate-limit=1M> for 1 megabit per
second.  C<0> means unlimited, which is the default.

=item B<file=>DISK.iso

Select the file from within the torrent to serve.

This parameter is optional.  If not specified then the plugin searches
the torrent for the largest file and serves that.  This is usually the
right thing to do for operating system installers and similar because
it serves the large F<.iso> file and ignores other files like READMEs.

The parameter is actually a path relative to the root directory of the
torrent, so if the torrent contains subdirectories you may need to use
a path like C<file=SUBDIR/DISK>.  To list all the files within the
torrent try running:

 $ nbdkit -fv torrent file.torrent

and examining the debug output.  As an alternative you can use
standard BitTorrent tools, eg:

 $ transmission-show file.torrent

=item B<listen-interfaces=>IP_ADDRESS:PORT[,IP_ADDRESS:PORT[,...]]

Listening ports that are opened for accepting incoming connections.
The parameter is a comma-separated list of C<IP-address:port>.

=item B<outgoing-interfaces=>IP_ADDRESS[,IP_ADDRESS[,...]]

Controls which IP address outgoing TCP connections are bound to.  The
parameter is a comma-separated list of IP addresses.

=item [B<torrent=>]FILEB<.torrent>

Specify a local torrent file.

=item [B<torrent=>]magnet:?xt=urn:...

Specify a L<magnet link|https://en.wikipedia.org/wiki/Magnet_URI_scheme>.

C<torrent=> __IS_MAGIC__

=item B<upload-rate-limit=>BITS_PER_SEC

Set the upload rate limit in bits per second.  Usual abbreviations can
be used such as C<upload-rate-limit=1M> for 1 megabit per second.
C<0> means unlimited, which is the default.

=item B<user-agent=>STRING

Set the user-agent.  The recommended format is
C<client-name/client-version>.  The default user agent can be found
using:

 nbdkit torrent --dump-plugin

=back

=head1 ENVIRONMENT VARIABLES

=over 4

=item C<TMPDIR>

This directory is used to cache the downloaded torrent file (or
F</var/tmp> if not set).  See also the C<cache=DIR> parameter above.

=back

=head1 FILES

=over 4

=item F<$plugindir/nbdkit-torrent-plugin.so>

The plugin.

Use C<nbdkit --dump-config> to find the location of C<$plugindir>.

=back

=head1 VERSION

C<nbdkit-torrent-plugin> first appeared in nbdkit 1.22.

=head1 SEE ALSO

L<nbdkit(1)>,
L<nbdkit-plugin(3)>,
L<nbdkit-curl-plugin(1)>,
L<nbdkit-file-plugin(1)>,
L<nbdkit-iso-plugin(1)>,
L<nbdkit-readahead-filter(1)>,
L<nbdkit-scan-filter(1)>,
L<transmission-show(1)>,
L<https://en.wikipedia.org/wiki/BitTorrent>,
L<http://libtorrent.org/>.

=head1 AUTHORS

Richard W.M. Jones

=head1 COPYRIGHT

Copyright Red Hat
