## Name

lwres_gabnrequest_render, lwres_gabnresponse_render, lwres_gabnrequest_parse, lwres_gabnresponse_parse, lwres_gabnresponse_free, lwres_gabnrequest_free — lightweight resolver getaddrbyname message handling

## Synopsis

    #include <lwres/lwres.h>

`lwres_result_t lwres_gabnrequest_render(` | lwres_context_t * | ctx,
| lwres_gabnrequest_t * | req,
| lwres_lwpacket_t * | pkt,
| lwres_buffer_t * | b`)`;

`lwres_result_t lwres_gabnresponse_render(` | lwres_context_t * | ctx,
| lwres_gabnresponse_t * | req,
| lwres_lwpacket_t * | pkt,
| lwres_buffer_t * | b`)`;

`lwres_result_t lwres_gabnrequest_parse(` | lwres_context_t * | ctx,
| lwres_buffer_t * | b,
| lwres_lwpacket_t * | pkt,
| lwres_gabnrequest_t ** | structp`)`;

`lwres_result_t lwres_gabnresponse_parse(` | lwres_context_t * | ctx,
| lwres_buffer_t * | b,
| lwres_lwpacket_t * | pkt,
| lwres_gabnresponse_t ** | structp`)`;

`void lwres_gabnresponse_free(` | lwres_context_t * | ctx,
| lwres_gabnresponse_t ** | structp`)`;

`void lwres_gabnrequest_free(` | lwres_context_t * | ctx,
| lwres_gabnrequest_t ** | structp`)`;

## DESCRIPTION

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

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

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

    #define LWRES_OPCODE_GETADDRSBYNAME     0x00010001U

    typedef struct lwres_addr lwres_addr_t;
    typedef LWRES_LIST(lwres_addr_t) lwres_addrlist_t;

    typedef struct {
            lwres_uint32_t  flags;
            lwres_uint32_t  addrtypes;
            lwres_uint16_t  namelen;
            char           *name;
    } lwres_gabnrequest_t;

    typedef struct {
            lwres_uint32_t          flags;
            lwres_uint16_t          naliases;
            lwres_uint16_t          naddrs;
            char                   *realname;
            char                  **aliases;
            lwres_uint16_t          realnamelen;
            lwres_uint16_t         *aliaslen;
            lwres_addrlist_t        addrs;
            void                   *base;
            size_t                  baselen;
    } lwres_gabnresponse_t;

`lwres_gabnrequest_render()` uses resolver context `ctx` to convert getaddrbyname 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_gabnresponse_render()` performs the same task, except it converts a getaddrbyname response structure lwres_gabnresponse_t to the lightweight resolver's canonical format.

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

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

## RETURN VALUES

The getaddrbyname opcode functions `lwres_gabnrequest_render()`, `lwres_gabnresponse_render()` `lwres_gabnrequest_parse()` and `lwres_gabnresponse_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_gabnrequest_t and lwres_gabnresponse_t structures. `lwres_gabnrequest_parse()` and `lwres_gabnresponse_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)