LWRES_RESUTIL(3)

NAME
lwres_string_parse, lwres_addr_parse, lwres_getaddrsbyname, lwres_getnamebyaddr - lightweight resolver utility functions

SYNOPSIS
#include <lwres/lwres.h>
lwres_result_t
lwres_string_parse(lwres_buffer_t *b, char **c, lwres_uint16_t *len);
lwres_result_t
lwres_addr_parse(lwres_buffer_t *b, lwres_addr_t *addr);
lwres_result_t
lwres_getaddrsbyname(lwres_context_t *ctx, const char *name, lwres_uint32_t addrtypes, lwres_gabnresponse_t **structp);
lwres_result_t
lwres_getnamebyaddr(lwres_context_t *ctx, lwres_uint32_t addrtype, lwres_uint16_t addrlen, const unsigned char *addr, lwres_gnbaresponse_t **structp);

DESCRIPTION
lwres_string_parse() retrieves a DNS-encoded string starting the current pointer of lightweight resolver buffer b: i.e. b->current. When the function returns, the address of the first byte of the encoded string is returned via *c and the length of that string is given by *len. The buffer's current pointer is advanced to point at the character following the string length, the encoded string, and the trailing NULL character. lwres_string_parse() has an assertion check that b is not NULL.

lwres_addr_parse() extracts an address from the buffer b. It checks that addr is not null. The buffer's current pointer b->current is presumed to point at an encoded address: the address preceded by a 32-bit protocol family identifier and a 16-bit length field. The encoded address is copied to addr->address and addr->length indicates the size in bytes of the address that was copied. b->current is advanced to point at the next byte of available data in the buffer following the encoded address.

lwres_getaddrsbyname() and lwres_getnamebyaddr() use the lwres_gnbaresponse_t structure defined below:

    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;

The contents of this structure are not manipulated directly but they are controlled through the lwres_gabn(3) functions.

The lightweight resolver uses lwres_getaddrsbyname() to perform foward lookups. Hostname name is looked up using the resolver context ctx for memory allocation. addrtypes is a bitmask indicating which type of addresses are to be looked up. Current values for this bitmask are LWRES_ADDRTYPE_V4 for IPv4 addresses and LWRES_ADDRTYPE_V6 for IPv6 addresses. Results of the lookup are returned in *structp. lwres_getaddrsbyname() checks that its pointer arguments are not NULL and that addrtypes is non-zero.

lwres_getnamebyaddr() performs reverse lookups. Resolver context ctx is used for memory allocation. The address type is indicated by addrtype: LWRES_ADDRTYPE_V4 or LWRES_ADDRTYPE_V6. The address to be looked up is given by addr and its length is addrlen bytes. The result of the function call is made available through *structp. Like lwres_getaddrsbyname(), lwres_getnamebyaddr() uses assertion checking to ensure its pointer arguments are not NULL and addrtype is not zero. lwres_getaddrsbyname() also checks that addrlen is non-zero.

RETURN VALUES
Successful calls to lwres_string_parse() and lwres_addr_parse() return LWRES_R_SUCCESS. Both functions return LWRES_R_FAILURE if the buffer is corrupt or LWRES_R_UNEXPECTEDEND if the buffer has less space than expected for the components of the encoded string or address.

lwres_getaddrsbyname() returns LWRES_R_SUCCESS on success and it returns LWRES_R_NOTFOUND if the hostname name could not be found.

LWRES_R_SUCCESS is returned by a successful call to lwres_getnamebyaddr().

Both lwres_getaddrsbyname() and lwres_getnamebyaddr() return LWRES_R_NOMEMORY when memory allocation requests fail and LWRES_R_UNEXPECTEDEND if the buffers used for sending queries and receiving replies are too small.

SEE ALSO
lwres_buffer(3), lwres_gabn(3).