lwres_getaddrinfo.html revision 8de7014e56565605a51898a2a33a8b08fd3f1e57
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<HTML
><HEAD
><TITLE
>lwres_getaddrinfo</TITLE
><META
NAME="GENERATOR"
CONTENT="Modular DocBook HTML Stylesheet Version 1.61
"></HEAD
><BODY
CLASS="REFENTRY"
BGCOLOR="#FFFFFF"
TEXT="#000000"
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ALINK="#0000FF"
><H1
><A
NAME="AEN1"
>lwres_getaddrinfo</A
></H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN8"
></A
><H2
>Name</H2
>lwres_getaddrinfo, lwres_freeaddrinfo -- socket address structure to host and service name</DIV
><DIV
CLASS="REFSYNOPSISDIV"
><A
NAME="AEN12"
></A
><H2
>Synopsis</H2
><DIV
CLASS="FUNCSYNOPSIS"
><A
NAME="AEN13"
></A
><P
></P
><PRE
CLASS="FUNCSYNOPSISINFO"
><P
><CODE
><CODE
CLASS="FUNCDEF"
>int
lwres_getaddrinfo</CODE
>(const char *hostname, const char *servname, const struct addrinfo *hints, struct addrinfo **res);</CODE
></P
><P
><CODE
><CODE
CLASS="FUNCDEF"
>void
lwres_freeaddrinfo</CODE
>(struct addrinfo *ai);</CODE
></P
><P
></P
></DIV
><P
>If the operating system does not provide a
<SPAN
CLASS="TYPE"
>struct addrinfo</SPAN
>,
the following structure is used:
<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
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN29"
></A
><H2
>DESCRIPTION</H2
><P
><TT
CLASS="FUNCTION"
>lwres_getaddrinfo()</TT
>
is used to get a list of IP addresses and port numbers for host
<TT
CLASS="PARAMETER"
><I
>hostname</I
></TT
>
and service
<TT
CLASS="PARAMETER"
><I
>servname</I
></TT
>.
The function is the lightweight resolver's implementation of
<TT
CLASS="FUNCTION"
>getaddrinfo()</TT
>
as defined in RFC2133.
<TT
CLASS="PARAMETER"
><I
>hostname</I
></TT
>
and
<TT
CLASS="PARAMETER"
><I
>servname</I
></TT
>
are pointers to null-terminated
strings or
<SPAN
CLASS="TYPE"
>NULL</SPAN
>.
<TT
CLASS="PARAMETER"
><I
>hostname</I
></TT
>
is either a host name or a numeric host address string: a dotted decimal
IPv4 address or an IPv6 address.
<TT
CLASS="PARAMETER"
><I
>servname</I
></TT
>
is either a decimal port number or a service name as listed in
<TT
CLASS="FILENAME"
>. </P
><P
><TT
CLASS="PARAMETER"
><I
>hints</I
></TT
>
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
<TT
CLASS="PARAMETER"
><I
>*hints</I
></TT
>:
<P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="CONSTANT"
>ai_family</TT
></DT
><DD
><P
>The protocol family that should be used.
When
<TT
CLASS="CONSTANT"
>ai_family</TT
>
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
><TT
CLASS="CONSTANT"
>ai_socktype</TT
></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
<TT
CLASS="CONSTANT"
>ai_socktype</TT
>
is zero the caller will accept any socket type.</P
></DD
><DT
><TT
CLASS="CONSTANT"
>ai_protocol</TT
></DT
><DD
><P
>indicates which transport protocol is wanted: IPPROTO_UDP or
IPPROTO_TCP.
If
<TT
CLASS="CONSTANT"
>ai_protocol</TT
>
is zero the caller will accept any protocol.</P
></DD
><DT
><TT
CLASS="CONSTANT"
>ai_flags</TT
></DT
><DD
><P
>Flag bits.
If the
<SPAN
CLASS="TYPE"
>AI_CANONNAME</SPAN
>
bit is set, a successful call to
<TT
CLASS="FUNCTION"
>lwres_getaddrinfo()</TT
>
will return a a null-terminated string containing the canonical name
of the specified hostname in
<TT
CLASS="CONSTANT"
>ai_canonname</TT
>
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
<TT
CLASS="CONSTANT"
>ai_flags</TT
>
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
<TT
CLASS="PARAMETER"
><I
>hostname</I
></TT
>
is a
<SPAN
CLASS="TYPE"
>NULL</SPAN
>
pointer and
<SPAN
CLASS="TYPE"
>AI_PASSIVE</SPAN
>
is not set in
<TT
CLASS="CONSTANT"
>ai_flags</TT
>. </P
><P
>If
<TT
CLASS="CONSTANT"
>ai_flags</TT
>
is set to
<SPAN
CLASS="TYPE"
>AI_NUMERICHOST</SPAN
>
it indicates that
<TT
CLASS="PARAMETER"
><I
>hostname</I
></TT
>
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
>All other elements of the
<SPAN
CLASS="TYPE"
>struct addrinfo</SPAN
>
passed via
<TT
CLASS="PARAMETER"
><I
>hints</I
></TT
>
must be zero.</P
><P
>A
<TT
CLASS="PARAMETER"
><I
>hints</I
></TT
>
of
<SPAN
CLASS="TYPE"
>NULL</SPAN
>
is treated as if the caller provided a
<SPAN
CLASS="TYPE"
>struct addrinfo</SPAN
>
initialized to zero with
<TT
CLASS="CONSTANT"
>ai_family</TT
>set to
<TT
CLASS="CONSTANT"
>PF_UNSPEC</TT
>. </P
><P
>After a successful call to
<TT
CLASS="FUNCTION"
>lwres_getaddrinfo()</TT
>,
<TT
CLASS="PARAMETER"
><I
>*res</I
></TT
>
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
<TT
CLASS="CONSTANT"
>ai_next</TT
>
pointer, until a
<SPAN
CLASS="TYPE"
>NULL</SPAN
>
pointer is encountered.
The three members
<TT
CLASS="CONSTANT"
>ai_family</TT
>,
<TT
CLASS="CONSTANT"
>ai_socktype</TT
>,
and
<TT
CLASS="CONSTANT"
>ai_protocol</TT
>
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
<TT
CLASS="CONSTANT"
>ai_addr</TT
>
member points to a filled-in socket address structure of length
<TT
CLASS="CONSTANT"
>ai_addrlen</TT
>. </P
><P
>All of the information returned by
<TT
CLASS="FUNCTION"
>lwres_getaddrinfo()</TT
>
is dynamically allocated: the addrinfo structures, and the socket
address structures and canonical host name strings pointed to by the
<TT
CLASS="CONSTANT"
>addrinfo</TT
>structures.
Memory allocated for the dynamically allocated structures created by
a successful call to
<TT
CLASS="FUNCTION"
>lwres_getaddrinfo()</TT
>
is released by
<TT
CLASS="FUNCTION"
>lwres_freeaddrinfo()</TT
>.
<TT
CLASS="PARAMETER"
><I
>ai</I
></TT
>
is a pointer to a
<SPAN
CLASS="TYPE"
>struct addrinfo</SPAN
>
created by a call to
<TT
CLASS="FUNCTION"
>lwres_getaddrinfo()</TT
>.</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN142"
></A
><H2
>RETURN VALUES</H2
><P
><TT
CLASS="FUNCTION"
>lwres_getaddrinfo()</TT
>
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
<TT
CLASS="PARAMETER"
><I
>hostname</I
></TT
>
and
<TT
CLASS="PARAMETER"
><I
>servname</I
></TT
>
are
<SPAN
CLASS="TYPE"
>NULL</SPAN
>
<TT
CLASS="FUNCTION"
>lwres_getaddrinfo()</TT
>
returns
<SPAN
CLASS="ERRORCODE"
>EAI_NONAME</SPAN
>. </P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN154"
></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
></DIV
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