June 18, 2007
lwres_noop 3 BIND9
2004 2005 2007 2014 Internet Systems Consortium, Inc. ("ISC")
2000 2001 Internet Software Consortium.
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

## 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