netwatch-dns: check with eworm.de and eworm.net

This should prevent against DENIC outages...

https://blog.denic.de/en/denic-reports-resolved-dnssec-disruption-affecting-de-domains/

global-functions.rsc

@@ -812,16 +812,16 @@
 # check if DNS is resolving
 :set IsDNSResolving do={
   :do {
-    :resolve "low-ttl.eworm.de";
-    :return true;
-  } on-error={ }
+    :local I 1;
+    :retry {
+      :set I ($I ^ 1);
+      :resolve ("low-ttl.eworm." . ({ "de"; "net" }->$I));
+    } delay=50ms max=6;
+  } on-error={
+    :return false;
+  }
 
-  :do {
-    :resolve "low-ttl.eworm.net";
-    :return true;
-  } on-error={ }
-
-  :return false;
+  :return true;
 }
 
 # check if system is is fully connected (default route reachable, DNS resolving, time sync)

netwatch-dns.rsc

@@ -115,13 +115,15 @@
 
     :local Data false;
     :onerror Err {
+      :local I 1;
       :retry {
+        :set I ($I ^ 1);
         :set Data ([ /tool/fetch check-certificate=yes-without-crl output=user \
           http-header-field=({ "accept: application/dns-message" }) \
           url=(($DohServer->"doh-url") . "?dns=" . [ :convert to=base64 ([ :rndstr length=2 ] . \
-          "\01\00" . "\00\01" . "\00\00" . "\00\00" . "\00\00" . "\09doh-check\05eworm\02de\00" . \
-          "\00\10" . "\00\01") ]) as-value ]->"data");
-      } delay=1s max=3;
+          "\01\00" . "\00\01" . "\00\00" . "\00\00" . "\00\00" . "\09doh-check\05eworm" . \
+          ({ "\02de"; "\03net" }->$I) . "\00" . "\00\10" . "\00\01") ]) as-value ]->"data");
+      } delay=500ms max=6;
     } do={
       $LogPrint warning $ScriptName ("Request to DoH server " . ($DohServer->"doh-url") . \
           " failed: " . $Err);