# lwres_gnba

## Name

lwres_gnbarequest_render, lwres_gnbaresponse_render, lwres_gnbarequest_parse, lwres_gnbaresponse_parse, lwres_gnbaresponse_free, lwres_gnbarequest_free -- lightweight resolver getnamebyaddress message handling

## Synopsis

    #include <lwres/lwres.h>

``lwres_result_t lwres_gnbarequest_render`(lwres_context_t *ctx, lwres_gnbarequest_t *req, lwres_lwpacket_t *pkt, lwres_buffer_t *b);`

``lwres_result_t lwres_gnbaresponse_render`(lwres_context_t *ctx, lwres_gnbaresponse_t *req, lwres_lwpacket_t *pkt, lwres_buffer_t *b);`

``lwres_result_t lwres_gnbarequest_parse`(lwres_context_t *ctx, lwres_buffer_t *b, lwres_lwpacket_t *pkt, lwres_gnbarequest_t **structp);`

``lwres_result_t lwres_gnbaresponse_parse`(lwres_context_t *ctx, lwres_buffer_t *b, lwres_lwpacket_t *pkt, lwres_gnbaresponse_t **structp);`

``void lwres_gnbaresponse_free`(lwres_context_t *ctx, lwres_gnbaresponse_t **structp);`

``void lwres_gnbarequest_free`(lwres_context_t *ctx, lwres_gnbarequest_t **structp);`

## DESCRIPTION

These are low-level routines for creating and parsing lightweight resolver address-to-name lookup request and response messages.

There are four main functions for the getnamebyaddr opcode. One render function converts a getnamebyaddr request structure — lwres_gnbarequest_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 getnamebyaddr request structure. Another render function converts the getnamebyaddr response structure — lwres_gnbaresponse_t to the canonical format. This is complemented by a parse function which converts a packet in canonical format to a getnamebyaddr response structure.

These structures are defined in `lwres/lwres.h`. They are shown below.

    #define LWRES_OPCODE_GETNAMEBYADDR      0x00010002U

    typedef struct {
            lwres_uint32_t  flags;
            lwres_addr_t    addr;
    } lwres_gnbarequest_t;

    typedef struct {
            lwres_uint32_t  flags;
            lwres_uint16_t  naliases;
            char           *realname;
            char          **aliases;
            lwres_uint16_t  realnamelen;
            lwres_uint16_t *aliaslen;
            void           *base;
            size_t          baselen;
    } lwres_gnbaresponse_t;

`lwres_gnbarequest_render()` uses resolver context `ctx` to convert getnamebyaddr 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_gnbaresponse_render()` performs the same task, except it converts a getnamebyaddr response structure lwres_gnbaresponse_t to the lightweight resolver's canonical format.

`lwres_gnbarequest_parse()` uses context `ctx` to convert the contents of packet `pkt` to a lwres_gnbarequest_t structure. Buffer `b` provides space to be used for storing this structure. When the function succeeds, the resulting lwres_gnbarequest_t is made available through `*structp`. `lwres_gnbaresponse_parse()` offers the same semantics as `lwres_gnbarequest_parse()` except it yields a lwres_gnbaresponse_t structure.

`lwres_gnbaresponse_free()` and `lwres_gnbarequest_free()` release the memory in resolver context `ctx` that was allocated to the lwres_gnbaresponse_t or lwres_gnbarequest_t structures referenced via `structp`. Any memory associated with ancillary buffers and strings for those structures is also discarded.

## RETURN VALUES

The getnamebyaddr opcode functions `lwres_gnbarequest_render()`, `lwres_gnbaresponse_render()` `lwres_gnbarequest_parse()` and `lwres_gnbaresponse_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_gnbarequest_t and lwres_gnbaresponse_t structures. `lwres_gnbarequest_parse()` and `lwres_gnbaresponse_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).