dhcp-to-dns: support host name from dhcp lease comment

The lease comment is supposed to be a human readable string... But we
could allow parsable information.

dhcp-to-dns.rsc

@@ -19,8 +19,10 @@
 :global ServerNameInZone;
 
 :global CharacterReplace;
+:global EitherOr;
 :global IfThenElse;
 :global LogPrintExit2;
+:global ParseKeyValueStore;
 :global ScriptLock;
 
 $ScriptLock $0 false 10;
@@ -62,7 +64,7 @@ $ScriptLock $0 false 10;
   :if ([ :len ($LeaseVal->"address") ] > 0) do={
     :local Comment ($CommentPrefix . $LeaseVal->"mac-address");
     :local MacDash [ $CharacterReplace ($LeaseVal->"mac-address") ":" "-" ];
-    :local HostName [ $CharacterReplace ($LeaseVal->"host-name") " " "" ];
+    :local HostName [ $CharacterReplace [ $EitherOr ([ $ParseKeyValueStore ($LeaseVal->"comment") ]->"hostname") ($LeaseVal->"host-name") ] " " "" ];
     :local Domain ([ $IfThenElse ($ServerNameInZone = true) ($LeaseVal->"server" . ".") ] . $Zone);
 
     :local DnsRecord [ /ip/dns/static/find where name=($MacDash . "." . $Domain) ];

doc/dhcp-to-dns.md

@@ -41,6 +41,19 @@ The configuration goes to `global-config-overlay`, these are the parameters:
 * `PrefixInZone`: whether or not to add prefix `dhcp`
 * `ServerNameInZone`: whether or not to add DHCP server name
 
+### Host name from DHCP lease comment
+
+Overwriting the host name from dhcp lease comment is supported, just add
+something like `hostname=new-hostname` in comment, and separate it by comma
+from other information if required:
+
+    /ip/dhcp-server/lease/add address=10.0.0.50 comment="my device, hostname=new-hostname" mac-address=00:11:22:33:44:55 server=dhcp;
+
+Note this information can be configured in wireless access list with
+[dhcp-lease-comment](dhcp-lease-comment.md), though it comes with a delay
+then due to script execution order. Decrease the scheduler interval to
+reduce the effect.
+
 See also
 --------