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       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);


       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

       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


       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.




       Copyright (C) 2004, 2005, 2007 Internet Systems Consortium, Inc.
       Copyright (C) 2000, 2001 Internet Software Consortium.