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<title>s6-networking: the s6-tlsserver program</title>
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<p>
<a href="index.html">s6-networking</a><br />
<a href="//skarnet.org/software/">Software</a><br />
<a href="//skarnet.org/">skarnet.org</a>
</p>
<h1> The <tt>s6-tlsserver</tt> program </h1>
<p>
<tt>s6-tlsserver</tt> is an
<a href="https://cr.yp.to/proto/ucspi.txt">UCSPI server tool</a> for
TLS/SSL connections over INET domain sockets. It acts as a TCP super-server
that listens to connections, accepts them, and for each connection,
establishes a TLS transport over it, then executes into a program.
</p>
<h2> Interface </h2>
<pre>
s6-tlsserver [ <em>options</em> ] [ -- ] <em>ip</em> <em>port</em> <em>prog...</em>
</pre>
<ul>
<li> s6-tlsserver rewrites itself into a command line
involving:
<ul>
<li> <a href="s6-tcpserver.html">s6-tcpserver</a>, which
listens to TCP connections on IP address <em>ip</em> port <em>port</em>
and forks a command line for every connection. Note that
<a href="s6-tcpserver.html">s6-tcpserver</a> also rewrites
itself into a more complex command line (the final long-lived
process being <a href="s6-tcpserverd.html">s6-tcpserverd</a>),
so your end command line may look a lot longer in <tt>ps</tt>
than what you originally wrote. This is normal and healthy. </li>
<li> (if applicable) <a href="s6-tcpserver-access.html">s6-tcpserver-access</a>,
which performs TCP access control and various operations on the
TCP connection. </li>
<li> <a href="s6-tlsd.html">s6-tlsd</a>, which establishes
a TLS transport (server-side) over a connection, via an
<a href="s6-tlsd-io.html">s6-tlsd-io</a> child process. </li>
<li> (if applicable)
<a href="//skarnet.org/software/s6/s6-applyuidgid.html">s6-applyuidgid</a>,
which drops root privileges. </li>
<li> <em>prog...</em>, your client program, which is run with the
same pid as <a href="s6-tlsd.html">s6-tlsd</a>. </li>
</ul> </li>
<li> It runs until it is killed by a signal. </li>
</ul>
<p>
<em>prog</em> is expected to read from its peer on its
standard input and write to its peer on its standard output.
Since there will be an <a href="s6-tlsd-io.html">s6-tlsd-io</a>
program between <em>prog</em> and the network to perform
the SSL encryption/decryption, those descriptors will not
be a network socket - they will be pipes.
</p>
<h2> Signals </h2>
<p>
<tt>s6-tlsserver</tt> reacts to the same signals as
<a href="s6-tcpserverd.html">s6-tcpserverd</a>,
which is the long-lived process hanging around.
</p>
<h2> Environment variables </h2>
<h3> Read </h3>
<p>
The following variables should be set before invoking
<tt>s6-tlsserver</tt>, because they will be used by
every <a href="s6-tlsd.html">s6-tlsd</a> invocation:
</p>
<ul>
<li> KEYFILE </li>
<li> CERTFILE </li>
<li> TLS_UID and TLS_GID (if you run <tt>s6-tlsserver</tt> as root) </li>
<li> CADIR (if you want client certificates) </li>
<li> CAFILE (if you want client certificates, alternative to CADIR) </li>
</ul>
<p>
Setting both KEYFILE and CERTFILE is mandatory.
</p>
<h3> Written </h3>
<p>
<em>prog...</em> is run with the following variables added to,
or removed from, its environment by <a href="s6-tcpserverd.html">s6-tcpserverd</a>
and possibly by <a href="s6-tcpserver-access.html">s6-tcpserver-access</a>:
</p>
<ul>
<li> PROTO </li>
<li> TCPREMOTEIP </li>
<li> TCPREMOTEPORT </li>
<li> TCPCONNNUM </li>
<li> TCPLOCALIP </li>
<li> TCPLOCALPORT </li>
<li> TCPREMOTEHOST </li>
<li> TCPLOCALHOST </li>
<li> TCPREMOTEINFO </li>
</ul>
<p>
Depending on TCP access rules (if the <tt>-i</tt> or <tt>-x</tt>
option has been given), it is possible that <em>prog</em>'s
environment undergoes more modifications. Also, since
<a href="s6-tlsd.html">s6-tlsd</a> is always run
after <a href="s6-tcpserver-access.html">s6-tcpserver-access</a>,
it is possible to set different TLS/SSL parameters (typically
a different KEYFILE and CERTFILE) depending on the client
connection, by writing the correct set of TCP access rules.
</p>
<p>
Unless the <tt>-Z</tt> option is given to <tt>s6-tlsserver</tt>,
the CADIR, CAFILE, KEYFILE, CERTFILE, TLS_UID and TLS_GID
variables will not appear in <em>prog</em>'s environment.
</p>
<h2> Options </h2>
<p>
<tt>s6-tlsserver</tt> accepts a myriad of options, all of which are
passed as is to the correct executable. Not giving any options will
generally work, but unless you're running a very public server
(such as a Web server) or base your access control on client
certificates, you probably still want TCP access rules.
</p>
<h3> Options passed as is to s6-tcpserver </h3>
<ul>
<li> <tt>-q</tt>, <tt>-Q</tt>, <tt>-v</tt> </li>
<li> <tt>-1</tt> </li>
<li> <tt>-c <em>maxconn</em></tt> </li>
<li> <tt>-C <em>localmaxconn</em></tt> </li>
<li> <tt>-b <em>backlog</em></tt> </li>
</ul>
<h3> Options passed as is to s6-tcpserver-access </h3>
<ul>
<li> The verbosity level, if not default, as <tt>-v0</tt> or <tt>-v2</tt> </li>
<li> <tt>-w</tt>, <tt>-W</tt> : be strict or tolerant with DNS or IDENT resolution errors </li>
<li> <tt>-d</tt>, <tt>-D</tt> : enable or disable Nagle's algorithm </li>
<li> <tt>-r</tt>, <tt>-R</tt> : enable or disable IDENT lookups </li>
<li> <tt>-p</tt>, <tt>-P</tt> : enable or disable paranoid DNS cross-checking </li>
<li> <tt>-h</tt>, <tt>-H</tt> : enable or disable DNS lookups </li>
<li> <tt>-l <em>localname</em></tt> : get the local name from the command line, not from DNS </li>
<li> <tt>-B <em>banner</em></tt> : initial server-side banner </li>
<li> <tt>-t <em>timeout</em></tt> : set a timeout for all the lookups </li>
<li> <tt>-i <em>rulesdir</em></tt>, <tt>-x <em>rulesfile</em></tt> : TCP access control </li>
</ul>
<h3> Options passed as is to s6-tlsd </h3>
<ul>
<li> <tt>-Z</tt>, <tt>-z</tt> : keep or remove the <a href="s6-tlsd-io.html">s6-tlsd-io</a>-specific
variables from the application's environment </li>
<li> <tt>-S</tt>, <tt>-s</tt> : use close_notify or EOF to signal the end of a TLS connection </li>
<li> <tt>-J</tt>, <tt>-j</tt> : exit nonzero with an error message when the peer fails to close_notify, or ignore it </li>
<li> <tt>-Y</tt>, <tt>-y</tt> : request an optional or a mandatory client certificate </li>
<li> <tt>-K <em>kimeout</em></tt> : set a timeout for the TLS handshake </li>
<li> <tt>-k <em>snilevel</em></tt> : support SNI-based certificate chains </li>
</ul>
<h3> Options passed to s6-applyuidgid </h3>
<ul>
<li> <tt>-u <em>uid</em></tt>, <tt>-g <em>gid</em></tt>, <tt>-G <em>gidlist</em></tt> : set uid, gid, or supplementary group list </li>
<li> <tt>-U</tt> (passed as <tt>-Uz</tt>) : get the uid, gid and supplementary group list from the UID, GID and GIDLIST variables,
and remove these variables from the application's environment </li>
</ul>
<h2> Example </h2>
<p>
As root:
</p>
<pre>env KEYFILE=/etc/ssl/private/mykey.der CERTFILE=/etc/ssl/public/mycert.pem \
TLS_UID=65534 TLS_GID=65534 \
s6-envuidgid www \
s6-tlsserver -U -- 1.2.3.4 443 httpd</pre>
<p>
This will start a server listening to 1.2.3.4 on TCP port 443,
and for every connection, spawn the <tt>httpd</tt> program
reading queries on stdin and replying on stdout, as user <tt>www</tt>,
with a TLS layer protecting the connection, the TLS engine running
as user <tt>nobody</tt> (<tt>65534:65534</tt>). The server is
authenticated by the certificate in <tt>/etc/ssl/public/mycert.pem</tt>
that it sends to the client, and the private key in
<tt>/etc/ssl/private/mykey.der</tt> that it keeps to itself.
</p>
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