lwres_getaddrinfo.html [plain text]
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<title>lwres_getaddrinfo</title>
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<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="refentry" lang="en">
<a name="id2476275"></a><div class="titlepage"></div>
<div class="refnamediv">
<h2>Name</h2>
<p>lwres_getaddrinfo, lwres_freeaddrinfo — socket address structure to host and service name</p>
</div>
<div class="refsynopsisdiv">
<h2>Synopsis</h2>
<div class="funcsynopsis">
<pre class="funcsynopsisinfo">#include <lwres/netdb.h></pre>
<table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" style="padding-bottom: 1em">
<tr>
<td><code class="funcdef">
int
<b class="fsfunc">lwres_getaddrinfo</b>(</code></td>
<td>const char * </td>
<td>
<var class="pdparam">hostname</var>, </td>
</tr>
<tr>
<td> </td>
<td>const char * </td>
<td>
<var class="pdparam">servname</var>, </td>
</tr>
<tr>
<td> </td>
<td>const struct addrinfo * </td>
<td>
<var class="pdparam">hints</var>, </td>
</tr>
<tr>
<td> </td>
<td>struct addrinfo ** </td>
<td>
<var class="pdparam">res</var><code>)</code>;</td>
</tr>
</table>
<table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0"><tr>
<td><code class="funcdef">
void
<b class="fsfunc">lwres_freeaddrinfo</b>(</code></td>
<td>struct addrinfo * </td>
<td>
<var class="pdparam">ai</var><code>)</code>;</td>
</tr></table>
</div>
<p>
If the operating system does not provide a
<span class="type">struct addrinfo</span>,
the following structure is used:
</p>
<pre class="programlisting">
struct addrinfo {
int ai_flags; /* AI_PASSIVE, AI_CANONNAME */
int ai_family; /* PF_xxx */
int ai_socktype; /* SOCK_xxx */
int ai_protocol; /* 0 or IPPROTO_xxx for IPv4 and IPv6 */
size_t ai_addrlen; /* length of ai_addr */
char *ai_canonname; /* canonical name for hostname */
struct sockaddr *ai_addr; /* binary address */
struct addrinfo *ai_next; /* next structure in linked list */
};
</pre>
<p>
</p>
</div>
<div class="refsect1" lang="en">
<a name="id2543416"></a><h2>DESCRIPTION</h2>
<p><code class="function">lwres_getaddrinfo()</code>
is used to get a list of IP addresses and port numbers for host
<em class="parameter"><code>hostname</code></em> and service
<em class="parameter"><code>servname</code></em>.
The function is the lightweight resolver's implementation of
<code class="function">getaddrinfo()</code> as defined in RFC2133.
<em class="parameter"><code>hostname</code></em> and
<em class="parameter"><code>servname</code></em> are pointers to null-terminated
strings or <span class="type">NULL</span>.
<em class="parameter"><code>hostname</code></em> is either a host name or a
numeric host address string: a dotted decimal IPv4 address or an
IPv6 address. <em class="parameter"><code>servname</code></em> is either a
decimal port number or a service name as listed in
<code class="filename">/etc/services</code>.
</p>
<p><em class="parameter"><code>hints</code></em>
is an optional pointer to a
<span class="type">struct addrinfo</span>.
This structure can be used to provide hints concerning the type of
socket
that the caller supports or wishes to use.
The caller can supply the following structure elements in
<em class="parameter"><code>*hints</code></em>:
</p>
<div class="variablelist"><dl>
<dt><span class="term"><code class="constant">ai_family</code></span></dt>
<dd><p>
The protocol family that should be used.
When
<code class="constant">ai_family</code>
is set to
<span class="type">PF_UNSPEC</span>,
it means the caller will accept any protocol family supported by
the
operating system.
</p></dd>
<dt><span class="term"><code class="constant">ai_socktype</code></span></dt>
<dd><p>
denotes the type of socket —
<span class="type">SOCK_STREAM</span>,
<span class="type">SOCK_DGRAM</span>
or
<span class="type">SOCK_RAW</span>
— that is wanted.
When
<code class="constant">ai_socktype</code>
is zero the caller will accept any socket type.
</p></dd>
<dt><span class="term"><code class="constant">ai_protocol</code></span></dt>
<dd><p>
indicates which transport protocol is wanted: IPPROTO_UDP or
IPPROTO_TCP.
If
<code class="constant">ai_protocol</code>
is zero the caller will accept any protocol.
</p></dd>
<dt><span class="term"><code class="constant">ai_flags</code></span></dt>
<dd>
<p>
Flag bits.
If the
<span class="type">AI_CANONNAME</span>
bit is set, a successful call to
<code class="function">lwres_getaddrinfo()</code>
will return a null-terminated string containing the canonical
name
of the specified hostname in
<code class="constant">ai_canonname</code>
of the first
<span class="type">addrinfo</span>
structure returned.
Setting the
<span class="type">AI_PASSIVE</span>
bit indicates that the returned socket address structure is
intended
for used in a call to
<span class="citerefentry"><span class="refentrytitle">bind</span>(2)</span>.
In this case, if the hostname argument is a
<span class="type">NULL</span>
pointer, then the IP address portion of the socket
address structure will be set to
<span class="type">INADDR_ANY</span>
for an IPv4 address or
<span class="type">IN6ADDR_ANY_INIT</span>
for an IPv6 address.
</p>
<p>
When
<code class="constant">ai_flags</code>
does not set the
<span class="type">AI_PASSIVE</span>
bit, the returned socket address structure will be ready
for use in a call to
<span class="citerefentry"><span class="refentrytitle">connect</span>(2)</span>
for a connection-oriented protocol or
<span class="citerefentry"><span class="refentrytitle">connect</span>(2)</span>,
<span class="citerefentry"><span class="refentrytitle">sendto</span>(2)</span>,
or
<span class="citerefentry"><span class="refentrytitle">sendmsg</span>(2)</span>
if a connectionless protocol was chosen.
The IP address portion of the socket address structure will be
set to the loopback address if
<em class="parameter"><code>hostname</code></em>
is a
<span class="type">NULL</span>
pointer and
<span class="type">AI_PASSIVE</span>
is not set in
<code class="constant">ai_flags</code>.
</p>
<p>
If
<code class="constant">ai_flags</code>
is set to
<span class="type">AI_NUMERICHOST</span>
it indicates that
<em class="parameter"><code>hostname</code></em>
should be treated as a numeric string defining an IPv4 or IPv6
address
and no name resolution should be attempted.
</p>
</dd>
</dl></div>
<p>
</p>
<p>
All other elements of the <span class="type">struct addrinfo</span> passed
via <em class="parameter"><code>hints</code></em> must be zero.
</p>
<p>
A <em class="parameter"><code>hints</code></em> of <span class="type">NULL</span> is
treated as if
the caller provided a <span class="type">struct addrinfo</span> initialized to zero
with <code class="constant">ai_family</code>set to
<code class="constant">PF_UNSPEC</code>.
</p>
<p>
After a successful call to
<code class="function">lwres_getaddrinfo()</code>,
<em class="parameter"><code>*res</code></em>
is a pointer to a linked list of one or more
<span class="type">addrinfo</span>
structures.
Each
<span class="type">struct addrinfo</span>
in this list cn be processed by following
the
<code class="constant">ai_next</code>
pointer, until a
<span class="type">NULL</span>
pointer is encountered.
The three members
<code class="constant">ai_family</code>,
<code class="constant">ai_socktype</code>,
and
<code class="constant">ai_protocol</code>
in each
returned
<span class="type">addrinfo</span>
structure contain the corresponding arguments for a call to
<span class="citerefentry"><span class="refentrytitle">socket</span>(2)</span>.
For each
<span class="type">addrinfo</span>
structure in the list, the
<code class="constant">ai_addr</code>
member points to a filled-in socket address structure of length
<code class="constant">ai_addrlen</code>.
</p>
<p>
All of the information returned by
<code class="function">lwres_getaddrinfo()</code>
is dynamically allocated: the addrinfo structures, and the socket
address structures and canonical host name strings pointed to by the
<code class="constant">addrinfo</code>structures.
Memory allocated for the dynamically allocated structures created by
a successful call to
<code class="function">lwres_getaddrinfo()</code>
is released by
<code class="function">lwres_freeaddrinfo()</code>.
<em class="parameter"><code>ai</code></em>
is a pointer to a
<span class="type">struct addrinfo</span>
created by a call to
<code class="function">lwres_getaddrinfo()</code>.
</p>
</div>
<div class="refsect1" lang="en">
<a name="id2543794"></a><h2>RETURN VALUES</h2>
<p><code class="function">lwres_getaddrinfo()</code>
returns zero on success or one of the error codes listed in
<span class="citerefentry"><span class="refentrytitle">gai_strerror</span>(3)</span>
if an error occurs. If both <em class="parameter"><code>hostname</code></em> and
<em class="parameter"><code>servname</code></em> are <span class="type">NULL</span>
<code class="function">lwres_getaddrinfo()</code> returns
<span class="errorcode">EAI_NONAME</span>.
</p>
</div>
<div class="refsect1" lang="en">
<a name="id2543831"></a><h2>SEE ALSO</h2>
<p><span class="citerefentry"><span class="refentrytitle">lwres</span>(3)</span>,
<span class="citerefentry"><span class="refentrytitle">lwres_getaddrinfo</span>(3)</span>,
<span class="citerefentry"><span class="refentrytitle">lwres_freeaddrinfo</span>(3)</span>,
<span class="citerefentry"><span class="refentrytitle">lwres_gai_strerror</span>(3)</span>,
<span class="citerefentry"><span class="refentrytitle">RFC2133</span></span>,
<span class="citerefentry"><span class="refentrytitle">getservbyname</span>(3)</span>,
<span class="citerefentry"><span class="refentrytitle">bind</span>(2)</span>,
<span class="citerefentry"><span class="refentrytitle">connect</span>(2)</span>,
<span class="citerefentry"><span class="refentrytitle">sendto</span>(2)</span>,
<span class="citerefentry"><span class="refentrytitle">sendmsg</span>(2)</span>,
<span class="citerefentry"><span class="refentrytitle">socket</span>(2)</span>.
</p>
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