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

#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); .SH "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 lighweight 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.

     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