concourse-curl-resource/assets/common.sh

set -e

# retrieve current file version
# e.g. curl -R -I $1
check_version() {
  # retrieves HTTP header of file URL response
  local httpHeader=$(curl -LR -I $1 2>&1 | grep 'Last-Modified:')
  # Checks if field "Last-Modified" exists in HTTP header and transform it into timestamp string
  # if that field is not present, return current timestamp
  local dateVersionFormat="%Y%m%d%H%S"
  local dateString=$(date +"$dateVersionFormat")

  if [ ! -z "$httpHeader" ]
  then
        # echo "Last-Modified information returned for targeted file. Extract date, removing day of the week string
        local tmpDateString=$(echo "$httpHeader" | sed -e "s/Last-Modified: //" | cut -d',' -f 2)
        # rfc1123Format="%d\ %b\ %Y\ %H:%M:%S\ GMT" - in order to work in boot2docker, it has to be outside of quotes in the command below
        local dateString=$(date +"$dateVersionFormat" -D %d\ %b\ %Y\ %H:%M:%S\ GMT -d "$tmpDateString")
  fi

  echo "{\"version\":\"$dateString\"}" | jq --slurp .
}