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LWRES_NOOP

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUES
SEE ALSO
AUTHOR
COPYRIGHT

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 {
uint16_t datalength;
unsigned char *data;
} lwres_nooprequest_t;

typedef struct {
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, 2018-2020 Internet Systems Consortium, Inc. ("ISC")