Use compression (if available) when downloading the ad lists.

Signed-off-by: DL6ER <dl6er@dl6er.de>

gravity.sh

@@ -311,7 +311,7 @@ gravity_SetDownloadOptions() {
 
 # Download specified URL and perform checks on HTTP status and file content
 gravity_DownloadBlocklistFromUrl() {
-  local url="${1}" cmd_ext="${2}" agent="${3}" heisenbergCompensator="" patternBuffer str httpCode success=""
+  local url="${1}" cmd_ext="${2}" agent="${3}" heisenbergCompensator="" patternBuffer str httpCode success="" compression
 
   # Create temp file to store content on disk instead of RAM
   patternBuffer=$(mktemp -p "/tmp" --suffix=".phgpb")
@@ -359,8 +359,18 @@ gravity_DownloadBlocklistFromUrl() {
     echo -ne "  ${INFO} ${str} Pending..."
     cmd_ext="--resolve $domain:$port:$ip $cmd_ext"
   fi
+
+  # Use compression to reduce the amount of data that is transfered
+  # between the Pi-hole and the ad list provider. Use this feature
+  # only if it is supported by the locally available version of curl
+  if curl -V | grep -q "Features:.* libz"; then
+    compression="--compressed"
+  else
+    compression=""
+  fi
+
   # shellcheck disable=SC2086
-  httpCode=$(curl -s -L ${cmd_ext} ${heisenbergCompensator} -w "%{http_code}" -A "${agent}" "${url}" -o "${patternBuffer}" 2> /dev/null)
+  httpCode=$(curl -s -L ${compression} ${cmd_ext} ${heisenbergCompensator} -w "%{http_code}" -A "${agent}" "${url}" -o "${patternBuffer}" 2> /dev/null)
 
   case $url in
     # Did we "download" a local file?