also support ip6.arpa in addition to ip6.int

CHANGES

@@ -2,6 +2,8 @@
   add errmsg API
   work around broken Linux sendfile API (offset 64-bit but count 32-bit)
   add io_appendfile, io_readwritefile
+  support ip6.arpa in addition to ip6.int in dns_name (adds one
+    parameter to dns_name6_domain and two constants in dns.h)
 
 0.19.2:
   for some reason, a botched dependency slipped in the the Makefile

dns.h

@@ -87,7 +87,9 @@ int dns_ip4_qualify(stralloc *,stralloc *,const stralloc *);
 int dns_ip6_qualify_rules(stralloc *,stralloc *,const stralloc *,const stralloc *);
 int dns_ip6_qualify(stralloc *,stralloc *,const stralloc *);
 
-int dns_name6_domain(char *,char *);
-#define DNS_NAME6_DOMAIN (4*16+10)
+#define DNS_IP6_INT 0
+#define DNS_IP6_ARPA 1
+int dns_name6_domain(char *,const char *,int);
+#define DNS_NAME6_DOMAIN (4*16+11)
 
 #endif

dns/dns_name.c

@@ -48,16 +48,23 @@ int dns_name4(stralloc *out,const char ip[4])
   return 0;
 }
 
-int dns_name6(stralloc *out,char ip[16])
+static int dns_name6_inner(stralloc *out,const char ip[16],int t)
 {
   char name[DNS_NAME6_DOMAIN];
 
-  if (ip6_isv4mapped(ip))
-    return dns_name4(out,ip+12);
-  dns_name6_domain(name,ip);
+  dns_name6_domain(name,ip,t);
   if (dns_resolve(name,DNS_T_PTR) == -1) return -1;
   if (dns_name_packet(out,dns_resolve_tx.packet,dns_resolve_tx.packetlen) == -1) return -1;
   dns_transmit_free(&dns_resolve_tx);
   dns_domain_free(&q);
   return 0;
 }
+
+int dns_name6(stralloc *out,const char ip[16])
+{
+  if (ip6_isv4mapped(ip))
+    return dns_name4(out,ip+12);
+  if (dns_name6_inner(out,ip,DNS_IP6_ARPA)) return -1;
+  if (!out->len) return dns_name6_inner(out,ip,DNS_IP6_INT);
+  return 0;
+}

dns/dns_name6.3

@@ -11,7 +11,10 @@ puts the (first) domain name into \fIout\fR and returns 0. If the relevant
 ip6.int domain does not exist in DNS, or has no PTR records, \fIout\fR
 will be empty.
 
-If dns_name4 has trouble with the DNS lookup or runs out of memory, it returns
+dns_name6 will try both the new "ip6.arpa" reverse lookup domain and the
+old (deprecated) "ip6.int" one.
+
+If dns_name6 has trouble with the DNS lookup or runs out of memory, it returns
 -1, setting errno appropriately. It may or may not change \fIout\fR.
 .SH "SEE ALSO"
 dns_name_packet(3), dns_name6_domain(3), dns_name4(3), dns_ip6(3)

dns/dns_name6_domain.3

@@ -5,11 +5,15 @@ dns_name6_domain \- construct host name for reverse lookup
 .B #include <dns.h>
 
 int \fBdns_name6_domain\fP(char \fIq\fR[DNS_NAME6_DOMAIN],
-                     const char* \fIip\fR[16]);
+                     const char* \fIip\fR[16],int \fItype\fR);
 .SH DESCRIPTION
 dns_name6_domain is a low-level component of dns_name6.  It converts an
 IP address such as 4321:0:1:2:3:4:567:89ab into a domain name such as
 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.INT
 and places the packet-encoded domain name into \fIq\fR.
+
+\fItype\fR can be DNS_IP6_INT or DNS_IP6_ARPA.  The "ip6.int" domain for
+IPv6 reverse lookups is now deprecated and "ip6.arpa" is the standard
+way.
 .SH "SEE ALSO"
 dns_name6(3), dns_name4_domain(3)

dns/dns_nd6.c

@@ -7,13 +7,14 @@
  *   4321:0:1:2:3:4:567:89ab
  * ->
  *   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.INT.
+ *   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.
  */
 
-static inline char tohex(char c) {
+static char tohex(char c) {
   return c>=10?c-10+'a':c+'0';
 }
 
-int dns_name6_domain(char name[DNS_NAME6_DOMAIN],char ip[16])
+int dns_name6_domain(char name[DNS_NAME6_DOMAIN],const char ip[16],int t)
 {
   unsigned int j;
 
@@ -23,7 +24,11 @@ int dns_name6_domain(char name[DNS_NAME6_DOMAIN],char ip[16])
     name[j*4+2]=1;
     name[j*4+3]=tohex((unsigned char)ip[15-j] >> 4);
   }
-  byte_copy(name + 4*16,9,"\3ip6\3int\0");
-  return 4*16+9;
+  if (t==DNS_IP6_INT)
+    byte_copy(name + 4*16,9,"\3ip6\3int\0");
+  else if (t==DNS_IP6_ARPA)
+    byte_copy(name + 4*16,10,"\3ip6\4arpa\0");
+  else return 0;
+  return 4*16+9+t;
 }