google expects a valid user agent to deliver the ics file

Added test if downloaded file is a ics file

icscheck/icscheck.conf.dist

@@ -5,6 +5,7 @@
 
 local icsconf_url="https://somethi.ng"
 local icsconf_output="${HOME}/my.ics"
+local icsconf_useragent="Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:109.0) Gecko/20100101 Firefox/110.0"
 
 # icsError
 # Called if the download from ${icsconf_url} failed

icscheck/icscheck.sh

@@ -77,13 +77,18 @@ icscheck() {
 
   mkdir -p "${ics_temp_dir}" "${ics_store_dir}"
 
-  wget -O "$ics_down_file" "$ics_url" >/dev/null 2>&1
+  curl -L "${ics_url}" -H "User-Agent: ${icsconf_useragent:?}" -o "${ics_down_file}" >/dev/null 2>&1
 
   # -s : exists and size greater zero
   if [ ! -s "$ics_down_file" ] || [ ! -r "$ics_down_file" ]; then
     icsError 
     exit 1
   fi
+  # check if ics file has VEVENTs
+  if ! grep -qE "(BEGIN:|END:)VEVENT" "${ics_down_file}"; then
+    icsError
+    exit 1
+  fi
 
   # Delete storage if manual renew is requested
   (( renew )) && rm -f "${ics_store_file}"