int dns_ip4_packet(stralloc *out,const char *buf,unsigned int len);
int dns_ip4(stralloc *out,stralloc *fqdn);
int dns_ip6_packet(stralloc *out,const char *buf,unsigned int len);
int dns_ip6(stralloc *out,stralloc *fqdn);
int dns_mx(stralloc *out,stralloc *fqdn);
int dns_mx_packet(stralloc *out,const char *buf,unsigned int len);
void dns_name4_domain(char q[DNS_NAME4_DOMAIN],const char *ip[4]);
int dns_name4(stralloc *out,const char *ip[4]);
void dns_name6_domain(char q[DNS_NAME6_DOMAIN],const char *ip[16]);
int dns_name6(stralloc *out,const char *ip[16]);
int dns_name(stralloc *out,const char *ip[16]);
int dns_name_packet(stralloc *out,const char *buf,unsigned int len);
int dns_txt(stralloc *out,stralloc *fqdn);
int dns_txt_packet(stralloc *out,const char *buf,unsigned int len);
int dns_cname(stralloc *out,stralloc *fqdn);
int dns_cname_packet(stralloc *out,const char *buf,unsigned int len);
int dns_ip4_qualify(stralloc *out,stralloc *fqdn,const stralloc *udn);
int dns_ip6_qualify(stralloc *out,stralloc *fqdn,const stralloc *udn);
int dns_ip_qualify(stralloc *out,stralloc *fqdn,const stralloc *udn);
dns_ip[4|6] looks up 4/16-byte IPv6 addresses for the fully qualified domain name of fqdn. It puts the concatenation of the IPv[4|6] addresses into out and returns the number of received answers for fqdn or 0 if none are replied. If the domain does not exist in DNS, or has no IP addresses, out will be empty. More generally, if fqdn is considered by dns_ip4 to be a dotted-decimal IPv4 address, it is provissioned as out without checking the DNS while returning 1. Brackets may enclose the dotted-decimal IP address; they are ignored.
dns_name[4|6]_packet is a low-level component of dns_name[4|6] designed to support asynchronous DNS lookups. It reads a DNS packet of length len from buf,
dns_name[4|6]_domain is a low-level component of dns_name[4|6]. It converts an IP address such as 1.2.3.4 or 4321:0:1:2:3:4:567:89ab into a domain name such as 4.3.2.1.in-addr.arpa or b.a.9.8.7.6.5.0.4.0.0.0.3.0.0.0.2.0.0.0.1.0.0.0.0.0.0.0.1.2.3.4.ip6.arpa and places the packet-encoded domain name into q. q is zero terminated. q must have space for DNS_NAME[4|6]_DOMAIN bytes.
dns_mx_packet is a low-level component of dns_mx, designed to support asynchronous DNS lookups. It reads a DNS packet of length len from buf, extracts the MX records from the answer section of the packet, puts the result into out, and returns the number of replies received or -1 the same way as dns_mx.
dns_mx looks up MX records for the fully-qualified domain name in fqdn. It puts the MX records into out and returns the number of received records or 0. Each MX record is a two-byte MX distance (big endian) followed by a \0-terminated dot-encoded domain name. If the domain does not exist in DNS, or has no MX records, out will be empty.
dns_txt_packet is a low-level component of dns_txt, designed to support asynchronous DNS lookups. It reads a DNS packet of length len from buf, extracts the TXT records from the answer section of the packet, puts the result into out, and returns the number of replies or -1 the same way as dns_txt.
dns_txt looks up TXT records for the fully-qualified domain name in fqdn. It puts the concatenation of the TXT records into out and returns the number of replies received. If the domain does not exist in DNS, or has no TXT records, out will be empty.
dns_cname_packet is a low-level component of dns_cname, designed to support asynchronous DNS lookups. It reads a DNS packet of length len from buf, extracts the TXT records from the answer section of the packet, puts the result into out, and returns the number of replies received or -1 the same way as dns_cname.
dns_cname looks up the canonical name for a given fqdn.
dns_ip[4|6]_qualify feeds the name udn through qualification and looks up their 4-byte/16-byte IP addresses. It puts the fully qualified domain name into fqdn and the concatenation of the IP addresses into out, while returning the number of encountered IP addresses. dns_ip[4|6]_qualify evaluates the environment variables $DNSREWRITEFILE pointing to /etc/dnsrewrite and $LOCALDOMAIN and finally reading /etc/resolv.conf to build the Full Qualified Domain Name (FQDN) using the domain suffix for hostname. dns_ip_qualify returns out as IP[4|6] and FQDN. If the domain does not exist in DNS, or has no IP addresses, out will be empty and the return code is 0.
In case dns_ip[4|6]_qualify is fed with an IP[4|6] addresses instead of domain names, it recognizes those not to be subject of qualification. The particular names localhost, ip4-loopback and ip6-loopback are treated locally and mapped to the respective IP[4|6] addresses (and vice versa) without facilitating a DNS lookup.
Value | Macro | Explaination
------+----------+-------------------------------------
n>0 | | n = number of answers reeceived
0 | DNS_NXD | either NXDOMAIN or NODATA
-1 | DNS_MEM | out of memory (fatal)
-2 | DNS_ERR | parsing errors
-3 | DNS_COM | socket communicaton errror; SERVFAIL
-4 | DNS_INT | internal error
-5 | DNS_SOFT | DNS_ERR or DNS_COM
-6 | DNS_HARD | DNS loop problem (CNAME)
errno is set appropriately. In case of a failure, the respective output variables like out and fqdn may or may not change. Since a received reply may be empty, always check the length of the received output additionally.