sslip.io returns AAAA (IPv6) records

- api.system.2a01-4f8-c17-b8f--2.sslip.io ➡ 2a01:4f8:c17:b8f::2
- `dashed` domains  only (e.g. only "fe80-2a01-4f8-c17--de0e" not
  "fe80.2a01.4f8.c17..de0e"; DNS doesn't allow two dots next to each
  other.
- mirrored from https://github.com/cunnie/bin/blob/master/pdns_pipe.sh
  which has colocated tests.

conf/sslip.io+nono.io.yml

@@ -43,6 +43,7 @@ pdns_pipe: |
   # `A` queries for the top-level domain will return this list of addresses.
   # CHANGEME: change this to your domain's webserver's address
   XIP_ROOT_ADDRESSES=( "52.0.56.137" )
+  XIP_ROOT_ADDRESSES_AAAA=( "2a01:4f8:c17:b8f::2" )
 
   # The public IP addresses on which this xip-pdns server will run.
   # `NS` queries for the top-level domain will return this list of addresses.
@@ -115,11 +116,12 @@ pdns_pipe: |
   #
   # xip.io domain helpers
   #
-  # note we insert "x{0}" to separate the double parentheses "((" to
-  # avoid BOSH interpolation getting confused and thinking it needs to insert
-  # a variable.
-  IP_PATTERN="(^|\.)(x{0}(x{0}(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?))($|\.)"
-  DASHED_IP_PATTERN="(^|-|\.)(x{0}(x{0}(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)-){3}(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?))($|-|\.)"
+  IP_PATTERN="(^|\.)(((25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?))($|\.)"
+  DASHED_IP_PATTERN="(^|-|\.)(((25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)-){3}(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?))($|-|\.)"
+  # https://stackoverflow.com/questions/53497/regular-expression-that-matches-valid-ipv6-addresses
+  # We don't use "dotted" IPv6 because DNS doesn't allow two dots next to each other
+  #   e.g. "::1" -> "1..sslip.io" isn't allowed (dig error: `is not a legal name (empty label)`)
+  DASHED_IPV6_PATTERN="(^|\.)(([0-9a-fA-F]{1,4}-){7,7}[0-9a-fA-F]{1,4}|([0-9a-fA-F]{1,4}-){1,7}-|([0-9a-fA-F]{1,4}-){1,6}-[0-9a-fA-F]{1,4}|([0-9a-fA-F]{1,4}-){1,5}(-[0-9a-fA-F]{1,4}){1,2}|([0-9a-fA-F]{1,4}-){1,4}(-[0-9a-fA-F]{1,4}){1,3}|([0-9a-fA-F]{1,4}-){1,3}(-[0-9a-fA-F]{1,4}){1,4}|([0-9a-fA-F]{1,4}-){1,2}(-[0-9a-fA-F]{1,4}){1,5}|[0-9a-fA-F]{1,4}-((-[0-9a-fA-F]{1,4}){1,6})|-((-[0-9a-fA-F]{1,4}){1,7}|-))(\.|$)"
 
   qtype_is() {
     [ "$QTYPE" = "$1" ] || [ "$QTYPE" = "ANY" ]
@@ -137,6 +139,10 @@ pdns_pipe: |
     [[ "$QNAME" =~ $DASHED_IP_PATTERN ]]
   }
 
+  subdomain_is_dashed_ipv6() {
+    [[ "$QNAME" =~ $DASHED_IPV6_PATTERN ]]
+  }
+
   resolve_ns_subdomain() {
     local index="${SUBDOMAIN:3}"
     echo "${XIP_NS_ADDRESSES[$index-1]}"
@@ -152,6 +158,11 @@ pdns_pipe: |
     echo "${BASH_REMATCH[2]//-/.}"
   }
 
+  resolve_dashed_ipv6_subdomain() {
+    [[ "$QNAME" =~ $DASHED_IPV6_PATTERN ]] || true
+    echo "${BASH_REMATCH[2]//-/:}"
+  }
+
   answer_soa_query() {
     send_answer "SOA" "$XIP_SOA"
   }
@@ -171,6 +182,13 @@ pdns_pipe: |
     done
   }
 
+  answer_root_aaaa_query() {
+    local address
+    for address in "${XIP_ROOT_ADDRESSES_AAAA[@]}"; do
+      send_answer "AAAA" "$address"
+    done
+  }
+
   answer_mx_query() {
     set -- "${XIP_MX_RECORDS[@]}"
     while [ $# -gt 1 ]; do
@@ -187,6 +205,14 @@ pdns_pipe: |
     fi
   }
 
+  answer_subdomain_aaaa_query_for() {
+    local type="$1"
+    local address="$(resolve_${type}_subdomain)"
+    if [ -n "$address" ]; then
+      send_answer "AAAA" "$address"
+    fi
+  }
+
 
   #
   # PowerDNS pipe backend implementation
@@ -219,5 +245,15 @@ pdns_pipe: |
       fi
     fi
 
+    if qtype_is "AAAA"; then
+      if [ $QNAME == $XIP_DOMAIN ]; then
+        answer_root_aaaa_query
+      else
+        if subdomain_is_dashed_ipv6; then
+          answer_subdomain_aaaa_query_for dashed_ipv6
+        fi
+      fi
+    fi
+
     send_cmd "END"
   done