lwres_gabn3

Usage

#include <lwres/lwres.h>

Overview

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 lightweight 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.