Handle v4-mapped IPv6 addresses sanely for --synth-domain.

CHANGELOG

@@ -24,7 +24,12 @@ version 2.77
 	    Bump zone serial on reloading /etc/hosts and friends
 	    when providing authoritative DNS. Thanks to Harrald
 	    Dunkel for spotting this.
-	
+
+	    Handle v4-mapped IPv6 addresses sanely in --synth-domain.
+	    These have standard representation like ::ffff:1.2.3.4
+	    and are now converted to names like
+	    <prefix>--ffff-1-2-3-4.<domain>
+
 
 version 2.76
             Include 0.0.0.0/8 in DNS rebind checks. This range 

man/dnsmasq.8

@@ -619,6 +619,8 @@ but IPv6 addresses may start with '::'
 but DNS labels may not start with '-' so in this case if no prefix is
 configured a zero is added in front of the label. ::1 becomes 0--1.
 
+V4 mapped IPv6 addresses, which have a representation like ::ffff:1.2.3.4 are handled specially, and become like 0--ffff-1-2-3-4
+
 The address range can be of the form
 <ip address>,<ip address> or <ip address>/<netmask>
 .TP

src/domain.c

@@ -77,18 +77,31 @@ int is_name_synthetic(int flags, char *name, struct all_addr *addr)
       
       *p = 0;	
       
-      /* swap . or : for - */
-      for (p = tail; *p; p++)
-	if (*p == '-')
-	  {
-	    if (prot == AF_INET)
+ #ifdef HAVE_IPV6
+      if (prot == AF_INET6 && strstr(tail, "--ffff-") == tail)
+	{
+	  /* special hack for v4-mapped. */
+	  memcpy(tail, "::ffff:", 7);
+	  for (p = tail + 7; *p; p++)
+	    if (*p == '-')
 	      *p = '.';
-#ifdef HAVE_IPV6
-	    else
-	      *p = ':';
+	}
+      else
 #endif
-	  }
-      
+	{
+	  /* swap . or : for - */
+	  for (p = tail; *p; p++)
+	    if (*p == '-')
+	      {
+		if (prot == AF_INET)
+		  *p = '.';
+#ifdef HAVE_IPV6
+		else
+		  *p = ':';
+#endif
+	      }
+	}
+
       if (hostname_isequal(c->domain, p+1) && inet_pton(prot, tail, addr))
 	{
 	  if (prot == AF_INET)
@@ -169,8 +182,9 @@ int is_rev_synth(int flag, struct all_addr *addr, char *name)
 	   inet_ntop(AF_INET6, &addr->addr.addr6, name+1, ADDRSTRLEN);
 	 }
 
+       /* V4-mapped have periods.... */
        for (p = name; *p; p++)
-	 if (*p == ':')
+	 if (*p == ':' || *p == '.')
 	   *p = '-';
 
        strncat(name, ".", MAXDNAME);