lwres_resutil.html [plain text]
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<HTML
><HEAD
><TITLE
>lwres_resutil</TITLE
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><H1
><A
NAME="AEN1"
>lwres_resutil</A
></H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN8"
></A
><H2
>Name</H2
>lwres_string_parse, lwres_addr_parse, lwres_getaddrsbyname, lwres_getnamebyaddr -- lightweight resolver utility functions</DIV
><DIV
CLASS="REFSYNOPSISDIV"
><A
NAME="AEN14"
></A
><H2
>Synopsis</H2
><DIV
CLASS="FUNCSYNOPSIS"
><A
NAME="AEN15"
></A
><P
></P
><PRE
CLASS="FUNCSYNOPSISINFO"
>#include <lwres/lwres.h></PRE
><P
><CODE
><CODE
CLASS="FUNCDEF"
>lwres_result_t
lwres_string_parse</CODE
>(lwres_buffer_t *b, char **c, lwres_uint16_t *len);</CODE
></P
><P
><CODE
><CODE
CLASS="FUNCDEF"
>lwres_result_t
lwres_addr_parse</CODE
>(lwres_buffer_t *b, lwres_addr_t *addr);</CODE
></P
><P
><CODE
><CODE
CLASS="FUNCDEF"
>lwres_result_t
lwres_getaddrsbyname</CODE
>(lwres_context_t *ctx, const char *name, lwres_uint32_t addrtypes, lwres_gabnresponse_t **structp);</CODE
></P
><P
><CODE
><CODE
CLASS="FUNCDEF"
>lwres_result_t
lwres_getnamebyaddr</CODE
>(lwres_context_t *ctx, lwres_uint32_t addrtype, lwres_uint16_t addrlen, const unsigned char *addr, lwres_gnbaresponse_t **structp);</CODE
></P
><P
></P
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN43"
></A
><H2
>DESCRIPTION</H2
><P
><TT
CLASS="FUNCTION"
>lwres_string_parse()</TT
> retrieves a DNS-encoded
string starting the current pointer of lightweight resolver buffer
<TT
CLASS="PARAMETER"
><I
>b</I
></TT
>: i.e. <TT
CLASS="CONSTANT"
>b->current</TT
>.
When the function returns, the address of the first byte of the
encoded string is returned via <TT
CLASS="PARAMETER"
><I
>*c</I
></TT
> and the
length of that string is given by <TT
CLASS="PARAMETER"
><I
>*len</I
></TT
>. The
buffer's current pointer is advanced to point at the character
following the string length, the encoded string, and the trailing
<SPAN
CLASS="TYPE"
>NULL</SPAN
> character.</P
><P
><TT
CLASS="FUNCTION"
>lwres_addr_parse()</TT
> extracts an address from the
buffer <TT
CLASS="PARAMETER"
><I
>b</I
></TT
>. The buffer's current pointer
<TT
CLASS="CONSTANT"
>b->current</TT
> is presumed to point at an encoded
address: the address preceded by a 32-bit protocol family identifier
and a 16-bit length field. The encoded address is copied to
<TT
CLASS="CONSTANT"
>addr->address</TT
> and
<TT
CLASS="CONSTANT"
>addr->length</TT
> indicates the size in bytes of
the address that was copied. <TT
CLASS="CONSTANT"
>b->current</TT
> is
advanced to point at the next byte of available data in the buffer
following the encoded address.</P
><P
><TT
CLASS="FUNCTION"
>lwres_getaddrsbyname()</TT
>
and
<TT
CLASS="FUNCTION"
>lwres_getnamebyaddr()</TT
>
use the
<SPAN
CLASS="TYPE"
>lwres_gnbaresponse_t</SPAN
>
structure defined below:
<PRE
CLASS="PROGRAMLISTING"
>typedef struct {
lwres_uint32_t flags;
lwres_uint16_t naliases;
lwres_uint16_t naddrs;
char *realname;
char **aliases;
lwres_uint16_t realnamelen;
lwres_uint16_t *aliaslen;
lwres_addrlist_t addrs;
void *base;
size_t baselen;
} lwres_gabnresponse_t;</PRE
>
The contents of this structure are not manipulated directly but
they are controlled through the
<SPAN
CLASS="CITEREFENTRY"
><SPAN
CLASS="REFENTRYTITLE"
>lwres_gabn</SPAN
>(3)</SPAN
>
functions.</P
><P
>The lightweight resolver uses
<TT
CLASS="FUNCTION"
>lwres_getaddrsbyname()</TT
> to perform foward lookups.
Hostname <TT
CLASS="PARAMETER"
><I
>name</I
></TT
> is looked up using the resolver
context <TT
CLASS="PARAMETER"
><I
>ctx</I
></TT
> for memory allocation.
<TT
CLASS="PARAMETER"
><I
>addrtypes</I
></TT
> is a bitmask indicating which type of
addresses are to be looked up. Current values for this bitmask are
<SPAN
CLASS="TYPE"
>LWRES_ADDRTYPE_V4</SPAN
> for IPv4 addresses and
<SPAN
CLASS="TYPE"
>LWRES_ADDRTYPE_V6</SPAN
> for IPv6 addresses. Results of the
lookup are returned in <TT
CLASS="PARAMETER"
><I
>*structp</I
></TT
>.</P
><P
><TT
CLASS="FUNCTION"
>lwres_getnamebyaddr()</TT
> performs reverse lookups.
Resolver context <TT
CLASS="PARAMETER"
><I
>ctx</I
></TT
> is used for memory
allocation. The address type is indicated by
<TT
CLASS="PARAMETER"
><I
>addrtype</I
></TT
>: <SPAN
CLASS="TYPE"
>LWRES_ADDRTYPE_V4</SPAN
> or
<SPAN
CLASS="TYPE"
>LWRES_ADDRTYPE_V6</SPAN
>. The address to be looked up is given
by <TT
CLASS="PARAMETER"
><I
>addr</I
></TT
> and its length is
<TT
CLASS="PARAMETER"
><I
>addrlen</I
></TT
> bytes. The result of the function call
is made available through <TT
CLASS="PARAMETER"
><I
>*structp</I
></TT
>.</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN84"
></A
><H2
>RETURN VALUES</H2
><P
>Successful calls to
<TT
CLASS="FUNCTION"
>lwres_string_parse()</TT
>
and
<TT
CLASS="FUNCTION"
>lwres_addr_parse()</TT
>
return
<SPAN
CLASS="ERRORCODE"
>LWRES_R_SUCCESS.</SPAN
>
Both functions return
<SPAN
CLASS="ERRORCODE"
>LWRES_R_FAILURE</SPAN
>
if the buffer is corrupt or
<SPAN
CLASS="ERRORCODE"
>LWRES_R_UNEXPECTEDEND</SPAN
>
if the buffer has less space than expected for the components of the
encoded string or address.</P
><P
><TT
CLASS="FUNCTION"
>lwres_getaddrsbyname()</TT
>
returns
<SPAN
CLASS="ERRORCODE"
>LWRES_R_SUCCESS</SPAN
>
on success and it returns
<SPAN
CLASS="ERRORCODE"
>LWRES_R_NOTFOUND</SPAN
>
if the hostname
<TT
CLASS="PARAMETER"
><I
>name</I
></TT
>
could not be found.</P
><P
><SPAN
CLASS="ERRORCODE"
>LWRES_R_SUCCESS</SPAN
>
is returned by a successful call to
<TT
CLASS="FUNCTION"
>lwres_getnamebyaddr()</TT
>.</P
><P
>Both
<TT
CLASS="FUNCTION"
>lwres_getaddrsbyname()</TT
>
and
<TT
CLASS="FUNCTION"
>lwres_getnamebyaddr()</TT
>
return
<SPAN
CLASS="ERRORCODE"
>LWRES_R_NOMEMORY</SPAN
>
when memory allocation requests fail and
<SPAN
CLASS="ERRORCODE"
>LWRES_R_UNEXPECTEDEND</SPAN
>
if the buffers used for sending queries and receiving replies are too
small.</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN105"
></A
><H2
>SEE ALSO</H2
><P
><SPAN
CLASS="CITEREFENTRY"
><SPAN
CLASS="REFENTRYTITLE"
>lwres_buffer</SPAN
>(3)</SPAN
>,
<SPAN
CLASS="CITEREFENTRY"
><SPAN
CLASS="REFENTRYTITLE"
>lwres_gabn</SPAN
>(3)</SPAN
>.</P
></DIV
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>