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RedHat 9 (Linux i386) - man page for lwres (redhat section 3)

LWRES(3)										 LWRES(3)

NAME
       lwres - introduction to the lightweight resolver library

SYNOPSIS
       #include <lwres/lwres.h>

DESCRIPTION
       The  BIND  9  lightweight  resolver  library  is  a  simple, name service independent stub
       resolver library. It provides hostname-to-address and address-to-hostname lookup  services
       to applications by transmitting lookup requests to a resolver daemon lwresd running on the
       local host. The resover daemon performs the lookup using the DNS or  possibly  other  name
       service	protocols,  and  returns the results to the application through the library.  The
       library and resolver daemon communicate using a simple UDP-based protocol.

OVERVIEW
       The lwresd library implements multiple name service APIs.  The  standard  gethostbyname(),
       gethostbyaddr(),  gethostbyname_r(),  gethostbyaddr_r(), getaddrinfo(), getipnodebyname(),
       and getipnodebyaddr() functions are all supported. To allow the lwres library  to  coexist
       with  system  libraries	that define functions of the same name, the library defines these
       functions with names prefixed by lwres_.  To define the standard names, applications  must
       include the header file <lwres/netdb.h> which contains macro definitions mapping the stan-
       dard function names into lwres_ prefixed ones. Operating system vendors who integrate  the
       lwres  library  into  their  base distributions should rename the functions in the library
       proper so that the renaming macros are not needed.

       The library also provides a native API consisting of the functions  lwres_getaddrsbyname()
       and lwres_getnamebyaddr().  These may be called by applications that require more detailed
       control over the lookup process than the standard functions provide.

       In addition to these name service independent address lookup functions, the library imple-
       ments  a  new,  experimental  API for looking up arbitrary DNS resource records, using the
       lwres_getaddrsbyname() function.

       Finally, there is a low-level API for converting lookup requests and responses to and from
       raw  lwres protocol packets.  This API can be used by clients requiring nonblocking opera-
       tion, and is also used when implementing the server side of the lwres protocol, for  exam-
       ple in the lwresd resolver daemon. The use of this low-level API in clients and servers is
       outlined in the following sections.

CLIENT-SIDE LOW-LEVEL API CALL FLOW
       When a client program wishes to make an lwres request using the native low-level  API,  it
       typically performs the following sequence of actions.

       (1) Allocate or use an existing lwres_packet_t, called pkt below.

       (2) Set pkt.recvlength to the maximum length we will accept.  This is done so the receiver
       of our packets knows how large our receive buffer is.  The  "default"  is  a  constant  in
       lwres.h: LWRES_RECVLENGTH = 4096.

       (3) Set pkt.serial to a unique serial number. This value is echoed back to the application
       by the remote server.

       (4) Set pkt.pktflags. Usually this is set to 0.

       (5) Set pkt.result to 0.

       (6) Call lwres_*request_render(), or marshall in the data using	the  primitives  such  as
       lwres_packet_render() and storing the packet data.

       (7) Transmit the resulting buffer.

       (8) Call lwres_*response_parse() to parse any packets received.

       (9)  Verify  that  the  opcode and serial match a request, and process the packet specific
       information contained in the body.

SERVER-SIDE LOW-LEVEL API CALL FLOW
       When implementing the server side of the lightweight resolver  protocol	using  the  lwres
       library, a sequence of actions like the following is typically involved in processing each
       request packet.

       Note that the same lwres_packet_t is used in both the _parse() and _render()  calls,  with
       only a few modifications made to the packet header's contents between uses. This method is
       recommended as it keeps the serial, opcode, and other fields correct.

       (1) When a packet is received, call lwres_*request_parse() to unmarshall it. This  returns
       a  lwres_packet_t  (also  called  pkt,  below)  as  well  as a data specific type, such as
       lwres_gabnrequest_t.

       (2) Process the request in the data specific type.

       (3) Set the pkt.result, pkt.recvlength as above. All other fields can  be  left	untouched
       since  they were filled in by the *_parse() call above. If using lwres_*response_render(),
       pkt.pktflags will be set  up  properly.	Otherwise,  the  LWRES_LWPACKETFLAG_RESPONSE  bit
       should be set.

       (4) Call the data specific rendering function, such as lwres_gabnresponse_render().

       (5) Send the resulting packet to the client.

SEE ALSO
       lwres_gethostent(3),	 lwres_getipnode(3),	 lwres_getnameinfo(3),	   lwres_noop(3),
       lwres_gabn(3), lwres_gnba(3), lwres_context(3), lwres_config(3), resolver(5), lwresd(8).

BIND9					   Jun 30, 2000 				 LWRES(3)


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