qlibs:

Section: Misc. Reference Manual Pages (dnsstub)
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NAME

dns - stub resolver

SYNTAX

#include "dnsresolv.h"

int dns_resolvconfip(char servers[512],uint32 scope[32]);

int dns_transmit_start(struct dns_transmit *q,const char servers[512],
    int flagrecursive,const char *q,const char qtype[2],
    const char localip[16]);
int dns_transmit_start6(struct dns_transmit *q,const char servers[512],
    int flagrecursive,const char *q,const char qtype[2],
    const char localip[16],const uint32 scopes[32]);

int dns_sortip4(char *servers,unsigned int n);
int dns_sortip6(char *servers,unsigned int n);

DESCRIPTION

dns_resolvconfip reads the name servers defined in /etc/resolv.conf and uses ip6_ifscan to fetch their IPv4/IPv6 addresses together with the scope for the LLU address. Up to 32 name servers can be specified.

Apart from the system-wide /etc/resolv.conf the IP addresses of name servers can preferrably be provided by means of the environment variable $DNSCACHEIP for each user application. The variable $DNSCACHEIP may include up to 32 name server IP addresses separated by white spaces:

DNSCACHEIP="10.0.1.53 fe80::1%lo0 ::1"

dns_transmit_start and dns_transmit_start6 use the list of name server IP's for a recursive or none-recursive query q of type qtype starting from IP address localip for which the struct dns_transmit provides the required book keeping information. dns_transmit_start6 additionally is able to evaluate the given scope_id as information for the local interface in order to bind to the remote IPv6 LLU addresses. Usually scope_id defaults to 0.

dns_sortip4 and dns_sortip6 randomize the list of name server IPs upon call and as result the first address is used to facilitate the name lookup. FQDN.

RETURN CODES

Different from the original djb implemtation, the following return code scheme is used:

rc > 0: A 'positive' answer is given, thus results returned.
rc = 0: A 'neutral' answer was provided, thus typically the operation succeeded, but without replies.
rc < 0: An operational error was encountered.
Potentially, this needs to be treated specifically:
DNS_INT (rc = -4): Internal DNS operational error; ie. resources were not available.
DNS_COM (rc = -3): DNS communication error.
DNS_ERR (rc = -2): Parsing errors and others.
DNS_MEM (rc = -1): Memory error occured.
A 'safe' usage of return codes thus checks not only the presence: of a return code, but rather additionally its sign. Negative return codes point to errors.