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<p>
<a href="index.html">tipidee</a><br />
<a href="//skarnet.org/software/">Software</a><br />
<a href="//skarnet.org/">skarnet.org</a>
</p>
<h1> The <tt>tipideed</tt> program </h1>
<p>
<tt>tipideed</tt> is the binary that actually does what you want from
a web server package: it serves files over HTTP.
</p>
<div id="interface">
<h2> Interface </h2>
</div>
<pre>
tipideed [ -v <em>verbosity</em> ] [ -f <em>cdbfile</em> ] [ -d <em>basedir</em> ] [ -R ] [ -U ]
</pre>
<ul>
<li> tipideed reads a stream of HTTP (1.0 or 1.1) requests on its stdin, and tries
to fulfill them, sending answers to stdout, and logs to stderr. </li>
<li> tipideed only speaks plaintext HTTP. It supports HTTPS, but the TLS layer
must be handled upstream by a program such as
<a href="//skarnet.org/software/s6-networking/s6-tlsd.html">s6-tlsd</a>. </li>
<li> tipideed stays alive until the client closes the connection, or times out,
or (in HTTP 1.1) sends a request with a <tt>Connection: close</tt> header; or an error
occurs that makes it nonsensical to keep the connection open. </li>
<li> By default, the documents it serves must be in subdirectories of its
current working directory, one subdirectory for every domain it hosts. </li>
</ul>
<div id="commonusage">
<h2> Common usage </h2>
</div>
<p>
tipideed 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>,
for plain text HTTP, or
<a href="//skarnet.org/software/s6-networking/s6-tlsserver.html">s6-tlsserver</a>,
for HTTPS. It delegates to the super-server the job of binding and listening to
the socket, accepting connections, spawning a separate process to handle a
given connection, and potentially establishing a TLS tunnel with the client for
secure communication.
</p>
<p>
As such, a command line for tipideed, running as user <tt>www</tt>, listening
on address <tt>${ip}</tt>, would typically look like this, for HTTP:
</p>
<pre>
s6-envuidgid www s6-tcpserver -U -- ${ip} 80 s6-tcpserver-access -- tipideed
</pre>
<p>
or, for HTTPS:
</p>
<pre>
s6-envuidgid www env KEYFILE=/path/to/private/key CERTFILE=/path/to/certificate s6-tlsserver -U -- ${ip} 443 tipideed
</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 tipidee package provides service templates to help you run tipideed 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 stream of HTTP exchanges,
that the client decided to end — including by being inactive long enough
that tipideed closes the connection on its own initiative, which is permitted
by HTTP. </dd>
<dt> 1 </dt> <dd> Illicit client behaviour. tipideed exited because it could
not serve the client in good faith. </dd>
<dt> 2 </dt> <dd> Illicit CGI script behaviour. tipideed exited because the invoked
CGI script made it impossible to continue. Before exiting, tipideed likely has
sent a 502 (Bad Gateway) response to the client. </dd>
<dt> 100 </dt> <dd> Bad usage. tipideed has been 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 tipideed, 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. tipideed found something in its configuration
data or in the document layout that it does not like. This can happen, for
instance, when a document is a symbolic link pointing outside of the server's
root. </dd>
<dt> 111 </dt> <dd> System call failed. If this happens while serving a request,
tipideed likely has sent a 500 (Internal Server Error) response to the
client before exiting. </dd>
</dl>
<div id="environment">
<h2> Environment variables </h2>
</div>
<h3> Reading - mandatory </h3>
<p>
tipideed expects the following variables in its environment, and will exit
with an error message if they are undefined. When tipideed is run under
<a href="//skarnet.org/s6-networking/s6-tcpserver.html">s6-tcpserver</a>
(with <a href="//skarnet.org/s6-networking/s6-tcpserver-access.html">s6-tcpserver-access</a>) or
<a href="//skarnet.org/s6-networking/s6-tlsserver.html">s6-tlsserver</a>,
these variables are automatically set by the super-server. This is the way
tipidee gets its network information without having to perform network
operations itself.
</p>
<dl>
<dt> PROTO </dt>
<dd> The network protocol, normally <tt>TCP</tt>. </dd>
<dt> TCPLOCALIP </dt>
<dd> The IP address the server is bound to. It will be passed as <tt>SERVER_ADDR</tt>
to CGI scripts. </dd>
<dt> TCPREMOTEIP </dt>
<dd> The IP address of the client. It will be passed as <tt>REMOTE_ADDR</tt>
to CGI scripts. </dd>
<dt> TCPREMOTEPORT </dt>
<dd> The port of the client socket. It will be passed as <tt>REMOTE_PORT</tt>
to CGI scripts. </dd>
</dl>
<h3> Reading - optional </h3>
<p>
tipideed can function without these variables, but if they're present, it
uses them to get more information.
</p>
<dl>
<dt> TCPLOCALHOST </dt>
<dd> The default domain name associated to the local IP address. It will be
passed as <tt>SERVER_NAME</tt> to CGI scripts when the requested URI does
not mention a Host, i.e. in HTTP/1.0 requests. If this variable is absent,
the default will be set to the local IP address itself (between square
brackets if IPv6). </dd>
<dt> TCPLOCALPORT </dt>
<dd> The port the server is bound to. It will be passed as <tt>SERVER_PORT</tt>
to CGI scripts unless the requested URI explicitly mentions a different port.
If this variable is absent, the default will be set to 80 in case of HTTP or
443 in the case of HTTPS. </dd>
<dt> TCPREMOTEHOST </dt>
<dd> The domain name associated to the IP address of the client. It will
be passed as <tt>REMOTE_HOST</tt> to CGI scripts; if absent, the value of
<tt>TCPREMOTEIP</tt> will be used instead. </dd>
<dt> TCPREMOTEINFO </dt>
<dd> The name provided by an IDENT server running on the client, if any.
This is obsolete and not expected to be present; but if present, it will
be passed as <tt>REMOTE_IDENT</tt> to CGI scripts. </dd>
<dt> SSL_PROTOCOL </dt>
<dd> The version of the TLS protocol used to cipher communications between
the client and the server. If present, tipideed will assume that the client
connection is secure, and will pass <tt>HTTPS=on</tt> to CGI scripts;
otherwise, it will assume it is running plaintext HTTP. </dd>
</dl>
<h3> Writing </h3>
<p>
When spawning a CGI or NPH script, tipideed clears all the previous variables,
so the passed environment is as close as possible to the environment of the
super-server; and it adds all the variables that are required by the
<a href="https://datatracker.ietf.org/doc/html/rfc3875#section-4.1">CGI 1.1
specification</a>. As an exception, it does not add PATH_TRANSLATED, which
cannot be used by CGI scripts in a portable way.
</p>
<div id="options">
<h2> Options </h2>
</div>
<dl>
<dt> -v <em>verbosity</em> </dt>
<dd> The level of log verbosity. This is the same as the <tt>global verbosity</tt>
setting in the <a href="tipidee.conf.html#verbosity">configuration file</a>; an explicit
command line option overrides any setting present in the configuration file.</dd>
<dt> -f <em>file</em> </dt>
<dd> Use <em>file</em> as the compiled configuration database, typically obtained
by running <tt><a href="tipidee-config.html">tipidee-config</a> -o <em>file</em></tt>.
The default is <tt>/etc/tipidee.conf.cdb</tt>; <tt>/etc</tt> may be something
else if the <tt>--sysconfdir</tt> option has been given to configure at
build time. </dd>
<dt> -d <em>docroot</em> </dt>
<dd> Change the working directory to <em>docroot</em> before serving. Default
is serving from the current working directory. Note that documents need to
be located in <strong>subdirectories</strong> of <em>docroot</em>, one subdirectory
per virtual domain tipideed is serving. </dd>
<dt> -R </dt>
<dd> chroot. If the underlying operating system has the
<a href="https://man7.org/linux/man-pages/man2/chroot.2.html">chroot()</a>
system call, use it before serving. This always happens <em>after</em> opening
the configuration database, <em>after</em> changing the working directory,
and <em>before</em> dropping privileges. The idea is that chrooting helps
with security, but the configuration database should be located outside of the
document space. </dd>
<dt> -U </dt>
<dd> Drop root privileges. If this option is given, tipideed expects two
additional environment variables, UID and GID, containing the uid and gid
it should run as; it will drop its privileges to $UID:$GID before serving.
This option is mainly useful when paired with <tt>-R</tt>, because chrooting
can only be performed as root, so root privileges need to be kept all the
way to tipideed then dropped after tipideed has chrooted. In a non-chrooted
setup, it is simpler and more secure to run the <em>super-server</em> with
the <tt>-U</tt> option instead: root privileges will be dropped as soon as
the super-server has bound to its socket, and all the subsequent operations,
including the spawning of tipideed processes, are performed as a normal user. </dd>
</dl>
<div id="docroot">
<h2> Document root </h2>
</div>
<p>
The way to organize your documents so they can be served by tipideed
may look a little weird, but there's a logic to it.
</p>
<p>
tipideed serves documents from subdirectories of its working directory,
and these subdirectories are named according to the host <em>and</em>
the port of the request.
</p>
<ul>
<li> A request for <tt>https://example.com:1234/doc/u/ment</tt>
will result in a lookup in the filesystem for
<tt>./example.com:1234/doc/u/ment</tt>. </li>
<li> A request for <tt>https://example.com/doc/u/ment</tt>
will result in a lookup in the filesystem for
<tt>./example.com:443/doc/u/ment</tt>. </li>
</ul>
<p>
The fact that the port is always specified allows you to have
different document sets for the same host on different ports:
more flexibility.
</p>
<p>
However, most of the time, you <em>don't</em> want different
document sets for different ports. You want the same document
sets for ports 80 and 443, and that's it. And you don't want
to have both a <tt>domain example.com:80</tt> section and a
<tt>domain example.com: 443</tt> section in your
<a href="tipidee.conf.html">/etc/tipidee.conf</a>, with
duplicate information.
</p>
<p>
That is why you are allowed to make your document roots
<em>symbolic links</em>, and resource attributes declared in
the configuration file are always looked up with the
<em>canonical path</em>. In other words, the common case
would be:
</p>
<ul>
<li> Have your document root in <tt>./example.com</tt>, a
real directory. </li>
<li> Declare your resource attributes under a
<tt>domain example.com</tt> section in your configuration file. </li>
<li> Have a <tt>./example.com:80</tt> symlink pointing to
<tt>example.com</tt>, if you want to serve <tt>example.com</tt>
under plaintext HTTP. </li>
<li> Have a <tt>./example.com:443</tt> symlink pointing to
<tt>example.com</tt>, if you want to serve <tt>example.com</tt>
under HTTPS. </li>
</ul>
<p>
This system allows you to share documents across virtual hosts
without fear of misconfiguration. You can symlink any document
under <tt>example.com</tt> to any name under <tt>example.org</tt>;
if the path via <tt>example.com</tt> is the canonical path, then
your resource will still get the correct attributes, defined in a
<tt>domain example.com</tt> section, even if it is accessed via an
<tt>example.org</tt> URL. You will not inadvertently expose source
code for CGI scripts, for instance.
</p>
<p>
You can do wild things with symbolic links. However, anything
that does not resolve to a file in a document root under tipideed's
current working directory will be rejected. If an attacker symlinks
your <tt>/etc/passwd</tt> file, tipideed will keep it safe.
</p>
<p>
HTTP/1.0 does not have the concepts of virtual hosts. For HTTP/1.0
requests that do not provide a full URL, tipideed will use a default
host name of <tt>@</tt> (at), so documents will likely be looked for
under <tt>@:80</tt> or <tt>@:443</tt>.
</p>
<div id="details">
<h2> Detailed operation </h2>
</div>
<ul>
<li> tipideed reads its <a href="tipidee-config.html">compiled</a>
configuration file. Then:
<ul>
<li> If the <tt>-d</tt> option has been given, it changes its working directory. </li>
<li> If the <tt>-R</tt> option has been given, it chroots to its current directory. </li>
<li> If the <tt>-U</tt> option has been given, it drops root privileges. </li>
</ul> </li>
<li> It checks that its environment is valid, and that its configuration has
some minimal defaults it can use. </li>
<li> tipideed listens to a stream of HTTP requests on its standard input. For every
HTTP request:
<ul>
<li> It parses the request line and check it's HTTP/1.0 or 1.1 </li>
<li> It parses the headers into a quick access structure </li>
<li> It checks header consistency with the request </li>
<li> If the method is <tt>OPTIONS *</tt> or <tt>TRACE</tt>, it answers here
and continues the loop </li>
<li> It reads the request body, if any </li>
<li> It checks in its configuration if a redirection has been defined for
the wanted resource or a prefix (by directory) of the wanted resource. If it's
the case, it answers with that redirection and continues the loop. </li>
<li> It looks for a suitable resource in the filesystem, completing the
request with index files if necessary, or extracting CGI INFO_PATHs if
necessary </li>
<li> It uses the canonical path of the resource in the filesystem to look
for resource attributes in its configuration. (Is this a CGI script? a NPH
script? Does it have a customized Content-Type? etc.) </li>
<li> If the method is a targeted <tt>OPTIONS</tt>, it answers here and
continues the loop </li>
<li> If the resource is a CGI script:
<ul>
<li> If it is an NPH script, tipideed execs into the script (possibly
after spawning a helper child if there is a request body to feed to the script)
with the appropriate environment;
and the connection will close when the script exits. </li>
<li> Else, tipideed spawns the CGI script as a child with the appropriate
environment, feeds it the request body if any, reads its output, and answers
the client. </li>
<li> If a problem occurs server-side, the client will receive a 502
answer ("Bad Gateway"), <em>and</em> tipideed will write an error message to
its stderr, so that administrators can see what went wrong with their setup.
tipideed trusts its CGI scripts more than its clients, but it does not give
them its full trust either — lots of sites are running third-party
backends. </li>
</ul> </li>
<li> Else, the resource is a regular ("static") file, and tipideed serves
it on its stdout, to the client. </li>
</ul> </li>
<li> tipideed exits on EOF (when the client closes the connection), or when
the client times out before sending a request, or after tipideed receives a
single HTTP/1.0 request, or when it has executed into an NPH script, or when
it has answered a request with a <tt>Connection: close</tt> header. It also
exits when it encounters an error making it likely that the client will have
no use for the connection anymore anyway and exiting is simpler and cheaper;
in which case tipideed adds <tt>Connection: close</tt> to its last answer. </li>
</ul>
<div id="performance">
<h2> Performance considerations </h2>
</div>
<p>
On systems that implement
<a href="https://pubs.opengroup.org/onlinepubs/9699919799/functions/posix_spawn.html">posix_spawn()</a>,
the <a href="//skarnet.org/software/s6-networking/s6-tcpserver.html">s6-tcpserver</a>
super-server (and the
<a href="//skarnet.org/software/s6-networking/s6-tlsserver.html">s6-tlsserver</a> one
as well, since both use the same underlying program) uses it instead of
<a href="https://pubs.opengroup.org/onlinepubs/9699919799/functions/fork.html">fork()</a>,
and that partly alleviates the performance penalty usually associated with servers
that spawn one process per connection.
</p>
<p>
One of tipidee's stated goals is to explore what kind of performance is achievable for
a fully compliant Web server within the limits of that model. To that effect, tipideed
is meant to be <em>fast</em>. It should serve static files as fast as any server out
there, especially on Linux (or other systems supporting
<a href="https://man7.org/linux/man-pages/man2/splice.2.html">splice())</a> where it
uses zero-copy transfer. CGI performance should be limited by the performance of the
CGI script itself, never by tipideed.
</p>
<p>
tipideed itself does not use
<a href="https://pubs.opengroup.org/onlinepubs/9699919799/functions/fork.html">fork()</a>
if the system supports
<a href="https://pubs.opengroup.org/onlinepubs/9699919799/functions/posix_spawn.html">posix_spawn()</a>
— with one exception, that you will not hit, and if you do, fork() will not
be the bottleneck. (Can you guess which case it is, without looking at the code?)
tipideed does not parse its configuration file itself, delegating the task to the
offline <a href="tipidee-config.html">tipidee-config</a> program and directly mapping
a binary file instead. To parse a client request, it uses a deterministic finite
automaton, only reading the request once, and only backtracking in pathological cases.
This should streamline request processing as much as possible.
</p>
<p>
If you have benchmarks, results of comparative testing of tipideed against
other Web servers, please share them on the
<a href="//skarnet.org/lists/#skaware">skaware mailing-list</a>.
</p>
<div id="notes">
<h2> Notes </h2>
</div>
<ul>
<li> tipideed sometimes answers 400, or even does not answer at all
(it just exits), when receiving some malformed or weirdly paced
client requests, despite what the
<a href="https://datatracker.ietf.org/doc/html/rfc9112">HTTP RFC</a> says.
This is on purpose. HTTP servers are very much solicited, they can run
very hot, the Web is a cesspool of bots and bad actors, and every
legitimate browser knows how to speak HTTP properly and without abusing
corner cases in the protocol.
It makes no sense to try to follow the book to the letter, expending
precious resources, when the client can't even be bothered to pretend
it's legit. Knowing when to exit early is crucial for good resource
management. </li>
<li> <tt>tipideed</tt> is pronounced <em>tipi-deed</em>. You can say
<em>tipi-dee-dee</em>, but only if you're the type of person who also says
<em>PC computer</em>, <em>NIC card</em> or <em>ATM machine</em>. </li>
<li> <tt>tipidee</tt> is the name of the <em>package</em>, the software suite
implementing a Web server. <tt>tipideed</tt> is the name of the <em>program</em>
doing the HTTP serving part. </li>
</ul>
</body>
</html>
|
