lwres_getaddrinfo.docbook [plain text]
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<refentry>
<refentryinfo>
<date>Jun 30, 2000</date>
</refentryinfo>
<refmeta>
<refentrytitle>lwres_getaddrinfo</refentrytitle>
<manvolnum>3</manvolnum>
<refmiscinfo>BIND9</refmiscinfo>
</refmeta>
<refnamediv>
<refname>lwres_getaddrinfo</refname>
<refname>lwres_freeaddrinfo</refname>
<refpurpose>socket address structure to host and service name</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcsynopsisinfo>#include <lwres/netdb.h></funcsynopsisinfo>
<funcprototype>
<funcdef>
int
<function>lwres_getaddrinfo</function></funcdef>
<paramdef>const char *hostname</paramdef>
<paramdef>const char *servname</paramdef>
<paramdef>const struct addrinfo *hints</paramdef>
<paramdef>struct addrinfo **res</paramdef>
</funcprototype>
<funcprototype>
<funcdef>
void
<function>lwres_freeaddrinfo</function></funcdef>
<paramdef>struct addrinfo *ai</paramdef>
</funcprototype>
</funcsynopsis>
<para>
If the operating system does not provide a
<type>struct addrinfo</type>,
the following structure is used:
<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 */
};
</programlisting>
</para>
</refsynopsisdiv>
<refsect1>
<title>DESCRIPTION</title>
<para>
<function>lwres_getaddrinfo()</function>
is used to get a list of IP addresses and port numbers for host
<parameter>hostname</parameter>
and service
<parameter>servname</parameter>.
The function is the lightweight resolver's implementation of
<function>getaddrinfo()</function>
as defined in RFC2133.
<parameter>hostname</parameter>
and
<parameter>servname</parameter>
are pointers to null-terminated
strings or
<type>NULL</type>.
<parameter>hostname</parameter>
is either a host name or a numeric host address string: a dotted decimal
IPv4 address or an IPv6 address.
<parameter>servname</parameter>
is either a decimal port number or a service name as listed in
<filename>/etc/services</filename>.
</para>
<para>
<parameter>hints</parameter>
is an optional pointer to a
<type>struct addrinfo</type>.
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
<parameter>*hints</parameter>:
<variablelist>
<varlistentry><term><constant>ai_family</constant></term>
<listitem>
<para>The protocol family that should be used.
When
<constant>ai_family</constant>
is set to
<type>PF_UNSPEC</type>,
it means the caller will accept any protocol family supported by the
operating system.
</para></listitem></varlistentry>
<varlistentry><term><constant>ai_socktype</constant></term>
<listitem>
<para>
denotes the type of socket —
<type>SOCK_STREAM</type>,
<type>SOCK_DGRAM</type>
or
<type>SOCK_RAW</type>
— that is wanted.
When
<constant>ai_socktype</constant>
is zero the caller will accept any socket type.
</para>
</listitem>
</varlistentry>
<varlistentry><term><constant>ai_protocol</constant></term>
<listitem>
<para>
indicates which transport protocol is wanted: IPPROTO_UDP or
IPPROTO_TCP.
If
<constant>ai_protocol</constant>
is zero the caller will accept any protocol.
</para>
</listitem>
</varlistentry>
<varlistentry><term><constant>ai_flags</constant></term>
<listitem>
<para>
Flag bits.
If the
<type>AI_CANONNAME</type>
bit is set, a successful call to
<function>lwres_getaddrinfo()</function>
will return a a null-terminated string containing the canonical name
of the specified hostname in
<constant>ai_canonname</constant>
of the first
<type>addrinfo</type>
structure returned.
Setting the
<type>AI_PASSIVE</type>
bit indicates that the returned socket address structure is intended
for used in a call to
<citerefentry>
<refentrytitle>bind</refentrytitle><manvolnum>2</manvolnum>
</citerefentry>.
In this case, if the hostname argument is a
<type>NULL</type>
pointer, then the IP address portion of the socket
address structure will be set to
<type>INADDR_ANY</type>
for an IPv4 address or
<type>IN6ADDR_ANY_INIT</type>
for an IPv6 address.
</para>
<para>
When
<constant>ai_flags</constant>
does not set the
<type>AI_PASSIVE</type>
bit, the returned socket address structure will be ready
for use in a call to
<citerefentry>
<refentrytitle>connect</refentrytitle><manvolnum>2
</manvolnum>
</citerefentry>
for a connection-oriented protocol or
<citerefentry>
<refentrytitle>connect</refentrytitle><manvolnum>2</manvolnum>
</citerefentry>,
<citerefentry>
<refentrytitle>sendto</refentrytitle><manvolnum>2</manvolnum>
</citerefentry>,
or
<citerefentry>
<refentrytitle>sendmsg</refentrytitle><manvolnum>2
</manvolnum>
</citerefentry>
if a connectionless protocol was chosen.
The IP address portion of the socket address structure will be
set to the loopback address if
<parameter>hostname</parameter>
is a
<type>NULL</type>
pointer and
<type>AI_PASSIVE</type>
is not set in
<constant>ai_flags</constant>.
</para>
<para>
If
<constant>ai_flags</constant>
is set to
<type>AI_NUMERICHOST</type>
it indicates that
<parameter>hostname</parameter>
should be treated as a numeric string defining an IPv4 or IPv6 address
and no name resolution should be attempted.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
<para>
All other elements of the <type>struct addrinfo</type> passed
via <parameter>hints</parameter> must be zero.
</para>
<para>
A <parameter>hints</parameter> of <type>NULL</type> is treated as if
the caller provided a <type>struct addrinfo</type> initialized to zero
with <constant>ai_family</constant>set to
<constant>PF_UNSPEC</constant>.
</para>
<para>
After a successful call to
<function>lwres_getaddrinfo()</function>,
<parameter>*res</parameter>
is a pointer to a linked list of one or more
<type>addrinfo</type>
structures.
Each
<type>struct addrinfo</type>
in this list cn be processed by following
the
<constant>ai_next</constant>
pointer, until a
<type>NULL</type>
pointer is encountered.
The three members
<constant>ai_family</constant>,
<constant>ai_socktype</constant>,
and
<constant>ai_protocol</constant>
in each
returned
<type>addrinfo</type>
structure contain the corresponding arguments for a call to
<citerefentry>
<refentrytitle>socket</refentrytitle><manvolnum>2</manvolnum>
</citerefentry>.
For each
<type>addrinfo</type>
structure in the list, the
<constant>ai_addr</constant>
member points to a filled-in socket address structure of length
<constant>ai_addrlen</constant>.
</para>
<para>
All of the information returned by
<function>lwres_getaddrinfo()</function>
is dynamically allocated: the addrinfo structures, and the socket
address structures and canonical host name strings pointed to by the
<constant>addrinfo</constant>structures.
Memory allocated for the dynamically allocated structures created by
a successful call to
<function>lwres_getaddrinfo()</function>
is released by
<function>lwres_freeaddrinfo()</function>.
<parameter>ai</parameter>
is a pointer to a
<type>struct addrinfo</type>
created by a call to
<function>lwres_getaddrinfo()</function>.
</para>
</refsect1>
<refsect1>
<title>RETURN VALUES</title>
<para>
<function>lwres_getaddrinfo()</function>
returns zero on success or one of the error codes listed in
<citerefentry>
<refentrytitle>gai_strerror</refentrytitle><manvolnum>3
</manvolnum>
</citerefentry>
if an error occurs.
If both
<parameter>hostname</parameter>
and
<parameter>servname</parameter>
are
<type>NULL</type>
<function>lwres_getaddrinfo()</function>
returns
<errorcode>EAI_NONAME</errorcode>.
</para>
</refsect1>
<refsect1>
<title>SEE ALSO</title>
<para>
<citerefentry>
<refentrytitle>lwres</refentrytitle><manvolnum>3</manvolnum>
</citerefentry>,
<citerefentry>
<refentrytitle>lwres_getaddrinfo</refentrytitle><manvolnum>3</manvolnum>
</citerefentry>,
<citerefentry>
<refentrytitle>lwres_freeaddrinfo</refentrytitle><manvolnum>3</manvolnum>
</citerefentry>,
<citerefentry>
<refentrytitle>lwres_gai_strerror</refentrytitle><manvolnum>3</manvolnum>
</citerefentry>,
<citerefentry>
<refentrytitle>RFC2133</refentrytitle>
</citerefentry>,
<citerefentry>
<refentrytitle>getservbyname</refentrytitle><manvolnum>3</manvolnum>
</citerefentry>,
<citerefentry>
<refentrytitle>bind</refentrytitle><manvolnum>2</manvolnum>
</citerefentry>,
<citerefentry>
<refentrytitle>connect</refentrytitle><manvolnum>2</manvolnum>
</citerefentry>,
<citerefentry>
<refentrytitle>sendto</refentrytitle><manvolnum>2</manvolnum>
</citerefentry>,
<citerefentry>
<refentrytitle>sendmsg</refentrytitle><manvolnum>2</manvolnum>
</citerefentry>,
<citerefentry>
<refentrytitle>socket</refentrytitle><manvolnum>2</manvolnum>
</citerefentry>.
</para>
</refsect1>
</refentry>