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<title>s6-networking: the ident library interface</title>
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<p>
<a href="index.html">libs6net</a><br />
<a href="../">s6-networking</a><br />
<a href="//skarnet.org/software/">Software</a><br />
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<h1> The <tt>ident</tt> library interface </h1>
<p>
The following functions and structures are declared in the <tt>s6-networking/ident.h</tt> header,
and implemented in the <tt>libs6net.a</tt> or <tt>libs6net.so</tt> library.
</p>
<h2> General information </h2>
<p>
<tt>ident</tt> provides a C IDENT client, following RFC 1413.
</p>
<p>
Please note that this protocol is of historical interest exclusively;
this client is only provided for convenience and interoperability with
legacy systems. The IDENT protocol absolutely cannot be relied on for
any kind of authentication or secure operation.
</p>
<h2> Functions </h2>
<p>
Check the <tt>s6-networking/ident.h</tt> header for the exact function prototypes.
</p>
<h3> Main interface </h3>
<p>
<code> ssize_t s6net_ident_client (char *s, size_t max, ip46_t const *remoteip, uint16_t remoteport, ip46_t const *localip, uint16_t localport,
tain_t const *deadline, tain_t *stamp) </code>
</p>
<p>
Makes an IDENT request to a server listening on IP <em>remoteip</em> port 113
about the connection from IP <em>remoteip</em> port <em>remoteport</em> to
IP <em>localip</em> port <em>localport</em>. Writes the answer into
preallocated string <em>s</em> of max length <em>max</em>, and returns the
number of bytes in the answer.
</p>
<ul>
<li> An <a href="//skarnet.org/software/skalibs/libstddjb/ip46.html">ip46_t</a>
is a structure holding either an IPv4 address or an IPv6 address. </li>
<li> If an error occurs, the function returns -1 and sets errno to a
suitable value. If no answer can be gotten from the server, the function
returns 0 and sets errno to a suitable value. </li>
<li> If <em>max</em> is too small for <em>s</em> to hold the answer, the
function returns -1 ENAMETOOLONG.
This can be avoided by using S6NET_IDENT_REPLY_SIZE
as <em>max</em>. </li>
<li> Negative answers are mapped to errno in the following way:
<ul>
<li> INVALID-PORT is reported as EINVAL </li>
<li> NO-USER is reported as ESRCH </li>
<li> HIDDEN-USER is reported as EPERM </li>
<li> UNKNOWN-ERROR is reported as EIO </li>
<li> extended error codes are reported as EEXIST </li>
</ul> </li>
<li> *<em>deadline</em> and *<em>stamp</em> are
<a href="//skarnet.org/software/skalibs/libstddjb/tai.h">absolute dates</a>:
*<em>stamp</em> must be an accurate enough approximation of the current time, and
is automatically updated when the function returns. If no answer has been gotten
from the server by *<em>deadline</em>, then the call is aborted and returns
-1 ETIMEDOUT. </li>
</ul>
<p>
<code> char const *s6net_ident_error_str (int e) </code>
</p>
<p>
Maps an error code representing a negative answer (i.e. errno when
<tt>s6net_ident_client</tt> returned 0) to a suitable string.
</p>
<h3> Low-level functions </h3>
<p>
<code> ssize_t s6net_ident_reply_get (char *s, ip46_t const *ra, uint16_t rp, ip46_t const *la, uint16_t lp,
tain_t const *deadline, tain_t *stamp) </code>
</p>
<p>
The network part of <tt>s6net_ident_client</tt>. Connects to *<em>ra</em>:113
and asks the server about (*<em>ra</em>:<em>rp</em>, *<em>la</em>:<em>lp</em>),
aborting if *<em>deadline</em> goes by. Writes the server answer into <em>s</em>;
at least S6NET_IDENT_REPLY_SIZE bytes must be preallocated in <em>s</em>.
Returns -1 if an error occurs, or the number of bytes written into <em>s</em>.
</p>
<p>
<code> ssize_t s6net_ident_reply_parse (char const *s, uint16_t rp, uint16_t lp) </code>
</p>
<p>
The local part of <tt>s6net_ident_client</tt>. Parses the server answer in
<em>s</em> for the connection from port <em>rp</em> to port <em>lp</em>.
Returns -1 EPROTO if the answer does not make sense, 0 if the answer is
negative, or a positive number if the answer is positive. This number is
an index where the ID can be found in <em>s</em>.
</p>
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