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")