fix pagination bug querying Linode API v4

fixes issue #4956

previous code only worked for the first 10 domains on the account (as Linode
API returned a paginated response, with only 10 records).

This change makes an exact search query for each subdomain, completely removing any
need for walking through paginated responses. What makes it work for large
accounts with any number of domains.

dnsapi/dns_linode_v4.sh

@@ -126,34 +126,41 @@ _Linode_API() {
 # _domain=domain.com
 # _domain_id=12345
 _get_root() {
-  domain=$1
+  local full_host_str="$1"
+
   i=2
   p=1
+  while true; do
+    # loop through the received string (e.g.  _acme-challenge.sub3.sub2.sub1.domain.tld),
+    # starting from the lowest subdomain, and check if it's a hosted domain
+    h=$(printf "%s" "$full_host_str" | cut -d . -f $i-100)
+    _debug h "$h"
+    if [ -z "$h" ]; then
+      #not valid
+      return 1
+    fi
 
-  if _rest GET; then
-    response="$(echo "$response" | tr -d "\n" | tr '{' "|" | sed 's/|/&{/g' | tr "|" "\n")"
-    while true; do
-      h=$(printf "%s" "$domain" | cut -d . -f $i-100)
-      _debug h "$h"
-      if [ -z "$h" ]; then
-        #not valid
-        return 1
-      fi
-
+   _debug "Querying Linode APIv4 for subdomain: $h"
+    if _H4="X-Filter: {\"domain\":\"$h\"}" _rest GET; then
+      _debug "Got response from API: $response"
+      response="$(echo "$response" | tr -d "\n" | tr '{' "|" | sed 's/|/&{/g' | tr "|" "\n")"
       hostedzone="$(echo "$response" | _egrep_o "\{.*\"domain\": *\"$h\".*}")"
       if [ "$hostedzone" ]; then
         _domain_id=$(printf "%s\n" "$hostedzone" | _egrep_o "\"id\": *[0-9]+" | _head_n 1 | cut -d : -f 2 | tr -d \ )
+        _debug "Found domain hosted on Linode DNS. Zone: $h, id: $_domain_id"
         if [ "$_domain_id" ]; then
-          _sub_domain=$(printf "%s" "$domain" | cut -d . -f 1-$p)
+          _sub_domain=$(printf "%s" "$full_host_str" | cut -d . -f 1-$p)
           _domain=$h
           return 0
         fi
         return 1
       fi
+
       p=$i
       i=$(_math "$i" + 1)
-    done
-  fi
+    fi
+  done
+
   return 1
 }
 
@@ -169,6 +176,7 @@ _rest() {
   export _H1="Accept: application/json"
   export _H2="Content-Type: application/json"
   export _H3="Authorization: Bearer $LINODE_V4_API_KEY"
+  export _H4 # used to query for the root domain on _get_root()
 
   if [ "$mtd" != "GET" ]; then
     # both POST and DELETE.