.TH dns_name4 3
.SH NAME
dns_name4 \- find FQDNs for IP addresses
.SH SYNTAX
.B #include <dns.h>

void \fBdns_name4\fP(&\fIout\fR,\fIip\fR);
.br
void \fBdns_name_packet\fP(&\fIout\fR,char *\fIbuf\fR,unsigned int \fIlen\fR);
.br
void \fBdns_name4_domain\fP(\fIq\fR,\fIip\fR);

stralloc \fIout\fR = {0};
.br
char \fIip\fR[4];
.br
char \fIq\fR[DNS_NAME4_DOMAIN];

.SH DESCRIPTION
.B dns_name4
looks up the domain name for the 4-byte IP address in \fIip\fR.  It puts the
(first) domain name into \fIout\fR and returns 0. If the relevant in-addr.arpa
domain does not exist in DNS, or has no PTR records, \fIout\fR will be empty.

If \fBdns_name4\fR has trouble with the DNS lookup or runs out of
memory, it returns -1, setting \fIerrno\fR appropriately. It may or may
not change \fIout\fR.

.B dns_name_packet
is a low-level component of \fBdns_name4\fR, designed to support
asynchronous DNS lookups. It reads a DNS packet of length \fIlen\fR from \fIbuf\fR,
extracts the first PTR record from the answer section of the packet, puts the
result into \fIout\fR, and returns 0 or -1 the same way as \fIdns_name4\fR.

.B dns_name4_domain
is another low-level component of \fBdns_name4\fR. It converts an IP address
such as 1.2.3.4 into a domain name such as 4.3.2.1.in-addr.arpa and
places the packet-encoded domain name into \fIq\fR.

.SH "SEE ALSO"
dns_ip4_qualify(3), dns_name6(3)