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<title>shibari: the shibari-server-tcp program</title>
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<p>
<a href="index.html">shibari</a><br />
<a href="//skarnet.org/software/">Software</a><br />
<a href="//skarnet.org/">skarnet.org</a>
</p>
<h1> The shibari-server-tcp program </h1>
<p>
shibari-server-tcp reads DNS queries on its standard input, and answers them
on its standard output.
</p>
<div id="interface">
<h2> Interface </h2>
</div>
<pre>
shibari-server-tcp [ -v <em>verbosity</em> [ -f <em>tdbfile</em> ] [ -r <em>rtimeout</em> ] [ -w <em>wtimeout</em> ]
</pre>
<ul>
<li> shibari-server-tcp reads a stream of DNS queries on its stdin (encoded
in the TCP DNS way, i.e. 2 bytes of length then the payload), and tries to fulfill them,
sending answers to stdout. It logs its actions to stderr. </li>
<li> It supports normal queries and AXFR queries. </li>
<li> It reads DNS data information from a
<a href="https://en.wikipedia.org/wiki/Cdb_(software)">cdb</a> database; the
database must use the output format from
<a href="https://cr.yp.to/djbdns/tinydns-data.html">tinydns-data</a>. </li>
</ul>
<div id="commonusage">
<h2> Common usage </h2>
</div>
<p>
shibari-server-tcp is intended to be run under a TCP super-server such as
<a href="//skarnet.org/software/s6-networking/s6-tcpserver.html">s6-tcpserver</a>.
It delegates to the super-server the job of binding and listening to
the socket, accepting connections, and spawning a separate process to handle a
given connection.
</p>
<p>
As such, a command line for shibari-server-tcp, running as user <tt>dns</tt>, listening
on address <tt>${ip}</tt>, would typically look like this:
</p>
<pre>
s6-envuidgid dns s6-tcpserver -U -- ${ip} 53 s6-tcpserver-access -x rules.cdb -- shibari-server-tcp
</pre>
<p>
Most users will want to run these command lines as <em>services</em>, i.e. daemons
run in the background when the machine starts. The <tt>examples/</tt> subdirectory
of the shibari package provides service templates to help you run shibari-server-tcp under
<a href="https://wiki.gentoo.org/wiki/OpenRC">OpenRC</a>,
<a href="//skarnet.org/software/s6/">s6</a> and
<a href="//skarnet.org/software/s6-rc/">s6-rc</a>.
</p>
<div id="exitcodes">
<h2> Exit codes </h2>
</div>
<dl>
<dt> 0 </dt> <dd> Clean exit. There was a successful series of DNS exchanges
and tipideed received EOF, or timed out while the client was idle. </dd>
<dt> 1 </dt> <dd> Invalid DNS query. The client spoke garbage. </dd>
<dt> 100 </dt> <dd> Bad usage. shibari-server-tcp was run in an incorrect way: bad command
line options, or missing environment variables, etc. </dd>
<dt> 101 </dt> <dd> Cannot happen. This signals a bug in shibari-server-tcp, and comes with an
error message asking you to report the bug. Please do so, on the
<a href="//skarnet.org/lists/#skaware">skaware mailing-list</a>. </dd>
<dt> 102 </dt> <dd> Misconfiguration. shibari-server-tcp found something in its DNS data file
that it does not like. </dd>
<dt> 111 </dt> <dd> System call failed. This usually signals an issue with the
underlying operating system. </dd>
</dl>
<div id="environment">
<h2> Environment variables </h2>
</div>
<p>
shibari-server-tcp expects the following variables in its environment, and will exit
with an error message if they are undefined. When run under
<a href="//skarnet.org/software/s6-networking/s6-tcpserver.html">s6-tcpserver</a>,
these variables are automatically set by the super-server. This is the way
shibari-server-tcp gets its network information without having to perform network
operations itself.
</p>
<dl>
<dt> TCPLOCALIP </dt>
<dd> The local IP address that the super-server is listening on. </dd>
<dt> TCPLOCALPORT </dt>
<dd> The local port that the super-server is listening on. In normal usage
this will be 53. </dd>
<dt> TCPREMOTEIP </dt>
<dd> The IP address of the client. </dd>
<dt> TCPREMOTEPORT </dt>
<dd> The remote port that the client is connecting from. </dd>
</dl>
<p>
The following variables are optional, but will inform shibari-server-tcp's
behaviour. They are typically set by
<a href="//skarnet.org/software/s6-networking/s6-tcpserver-access.html">s6-tcpserver-access</a>
with the <tt>-i</tt> or <tt>-x</tt> option, when the access rules database
defines environment variables depending on client IP ranges.
</p>
<dl>
<dt> AXFR </dt>
<dd> If this variable is set, it controls what zones the client is allowed
to make AXFR queries for. A value of <tt>*</tt> (star) means the client is
allowed to make AXFR queries for any zone, same as when the variable is not
defined. Else, the value needs to be a space-, comma-, semicolon-, or
slash-separated list of zones; these are the allowed zones. </dd>
<dt> LOC </dt>
<dd> If this variable is set, it defines a client location that is used to
implement views. A client location is at most two charaters; if the value
is <tt>lo</tt>, then the client will be granted access to DNS data guarded
by a <tt>%lo</tt> location indicator in the
<a href="https://cr.yp.to/djbdns/tinydns-data.html">tinydns-data</a> file.
Note that shibari-server-tcp ignores client IP prefix matching compiled in
the database via <tt>%lo:ipprefix</tt> lines: it only takes its location
information from the LOC variable, and will use the contents of LOC to match
lines ending with <tt>:%lo</tt>. The idea is to only have one place centralizing
what clients are authorized to do depending on their IP, and that place is the
<a href="//skarnet.org/software/s6-networking/s6-tcpserver-access.html">s6-tcpserver-access</a>
rules database. </dd>
</dl>
<div id="options">
<h2> Options </h2>
</div>
<dl>
<dt> -v <em>verbosity</em> </dt>
<dd> Be more or less verbose.
A <em>verbosity</em> of 0 means no warnings, no logs, only error messages. 1
means warnings and terse logs. 2 or more means more logs.
Default is <strong>1</strong>. </dd>
<dt> -f <em>tdbfile</em> </dt>
<dd> Read DNS data from <em>tdbfile</em>.
The default is <strong><tt>data.cdb</tt></strong>, in the current working
directory of the shibari-server-tcp process. </dd>
<dt> -r <em>rtimeout</em> </dt>
<dd> Read timeout. If <em>rtimeout</em> milliseconds
elapse while shibari-server-tcp is waiting for a DNS query, just exit.
The default is <strong>0</strong>, meaning infinite: shibari-server-tcp
will never close the connection until it receives EOF. </dd>
<dt> -w <em>wtimeout</em> </dt>
<dd> Write timeout. If shibari-server-tcp is unable
to send its answer in <em>wtimeout</em> milliseconds, which means the network is
congested, give up and close the connection. The default is <strong>0</strong>, which
means infinite: shibari-server-tcp will wait forever until the network decongests in
order to send its answer. </dd>
</dl>
<div id="notes">
<h2> Notes </h2>
</div>
<ul>
<li> The DNS database can be changed at any time via an invocation of
<a href="https://cr.yp.to/djbdns/tinydns-data.html">tinydns-data</a>.
shibari-server-tcp will keep using the old data until its current stream
ends and it exits. The next instance of shibari-server-tcp,
spawned by the super-server, will use the new data. </li>
<li> shibari-server-tcp is a drop-in replacement for
<a href="https://cr.yp.to/djbdns/axfrdns.html">axfrdns</a>, with one
caveat: client location information needs to be migrated from the DNS
database to LOC definitions in the TCP access rules database. For instance,
if you have a <tt>%lo:1.2.3</tt> line in your text data file, you need to
add the following entries to your TCP access rules database:
<ul>
<li> <tt>ip4/1.2.3.0_24/allow</tt> (may be empty) </li>
<li> <tt>ip4/1.2.3.0_24/env/LOC</tt> containing <tt>lo</tt> </li>
</ul> </li>
<li> If you are using such an access rules database via a
<a href="//skarnet.org/software/s6-networking/s6-tcpserver-access.html">s6-tcpserver-access</a>
invocation, make sure your
<a href="shibari-server-udp.html">shibari-server-udp</a> service is using the
same database via the <tt>-i</tt> or <tt>-x</tt> option. You
don't want to give different permissions, or different location information,
depending on whether a query is made over TCP or UDP. </li>
</ul>
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