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, 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, uint32_t addrtypes, lwres_gabnresponse_t **structp);

lwres_result_t lwres_getnamebyaddr(lwres_context_t *ctx, uint32_t addrtype, 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_addr_parse() extracts an address from the buffer b. 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 {


        uint32_t          flags;


        uint16_t          naliases;


        uint16_t          naddrs;


        char                   *realname;


        char                  **aliases;


        uint16_t          realnamelen;


        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 forward 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_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.

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).

AUTHOR¶

Internet Systems Consortium, Inc.

COPYRIGHT¶

Copyright © 2000, 2001, 2004, 2005, 2007, 2014-2016, 2018-2021 Internet Systems Consortium, Inc. ("ISC")