NAME

       lwres_nooprequest_render, lwres_noopresponse_render, lwres_nooprequest_parse, lwres_noopresponse_parse,
       lwres_noopresponse_free, lwres_nooprequest_free - lightweight resolver no-op message handling

SYNOPSIS

       #include <lwres/lwres.h>

       lwres_result_t lwres_nooprequest_render(lwres_context_t *ctx, lwres_nooprequest_t *req,
                                               lwres_lwpacket_t *pkt, lwres_buffer_t *b);

       lwres_result_t lwres_noopresponse_render(lwres_context_t *ctx, lwres_noopresponse_t *req,
                                                lwres_lwpacket_t *pkt, lwres_buffer_t *b);

       lwres_result_t lwres_nooprequest_parse(lwres_context_t *ctx, lwres_buffer_t *b, lwres_lwpacket_t *pkt,
                                              lwres_nooprequest_t **structp);

       lwres_result_t lwres_noopresponse_parse(lwres_context_t *ctx, lwres_buffer_t *b, lwres_lwpacket_t *pkt,
                                               lwres_noopresponse_t **structp);

       void lwres_noopresponse_free(lwres_context_t *ctx, lwres_noopresponse_t **structp);

       void lwres_nooprequest_free(lwres_context_t *ctx, lwres_nooprequest_t **structp);

DESCRIPTION

       These are low-level routines for creating and parsing lightweight resolver no-op request and response
       messages.

       The no-op message is analogous to a ping packet: a packet is sent to the resolver daemon and is simply
       echoed back. The opcode is intended to allow a client to determine if the server is operational or not.

       There are four main functions for the no-op opcode. One render function converts a no-op request
       structure — lwres_nooprequest_t — to the lightweight resolver's canonical format. It is complemented by a
       parse function that converts a packet in this canonical format to a no-op request structure. Another
       render function converts the no-op response structure — lwres_noopresponse_t to the canonical format.
       This is complemented by a parse function which converts a packet in canonical format to a no-op response
       structure.

       These structures are defined in lwres/lwres.h. They are shown below.

           #define LWRES_OPCODE_NOOP       0x00000000U

           typedef struct {
                   lwres_uint16_t  datalength;
                   unsigned char   *data;
           } lwres_nooprequest_t;

           typedef struct {
                   lwres_uint16_t  datalength;
                   unsigned char   *data;
           } lwres_noopresponse_t;

       Although the structures have different types, they are identical. This is because the no-op opcode simply
       echos whatever data was sent: the response is therefore identical to the request.

       lwres_nooprequest_render() uses resolver context ctx to convert no-op request structure req to canonical
       format. The packet header structure pkt is initialised and transferred to buffer b. The contents of *req
       are then appended to the buffer in canonical format.  lwres_noopresponse_render() performs the same task,
       except it converts a no-op response structure lwres_noopresponse_t to the lightweight resolver's
       canonical format.

       lwres_nooprequest_parse() uses context ctx to convert the contents of packet pkt to a lwres_nooprequest_t
       structure. Buffer b provides space to be used for storing this structure. When the function succeeds, the
       resulting lwres_nooprequest_t is made available through *structp.  lwres_noopresponse_parse() offers the
       same semantics as lwres_nooprequest_parse() except it yields a lwres_noopresponse_t structure.

       lwres_noopresponse_free() and lwres_nooprequest_free() release the memory in resolver context ctx that
       was allocated to the lwres_noopresponse_t or lwres_nooprequest_t structures referenced via structp.

RETURN VALUES

       The no-op opcode functions lwres_nooprequest_render(),
       lwres_noopresponse_render()lwres_nooprequest_parse() and lwres_noopresponse_parse() all return
       LWRES_R_SUCCESS on success. They return LWRES_R_NOMEMORY if memory allocation fails.
       LWRES_R_UNEXPECTEDEND is returned if the available space in the buffer b is too small to accommodate the
       packet header or the lwres_nooprequest_t and lwres_noopresponse_t structures.  lwres_nooprequest_parse()
       and lwres_noopresponse_parse() will return LWRES_R_UNEXPECTEDEND if the buffer is not empty after
       decoding the received packet. These functions will return LWRES_R_FAILURE if pktflags in the packet
       header structure lwres_lwpacket_t indicate that the packet is not a response to an earlier query.

SEE ALSO

       lwres_packet(3)

AUTHOR

       Internet Systems Consortium, Inc.

COPYRIGHT

       Copyright © 2000, 2001, 2004, 2005, 2007, 2014-2016 Internet Systems Consortium, Inc. ("ISC")