header-filter.yaml

apiVersion: networking.istio.io/v1alpha3
kind: EnvoyFilter
metadata:
  name: cache-control-header-envoy-filter
spec:
  workloadLabels:
    app: app-name
  filters:
    - listenerMatch:
        portNumber: 80
        listenerType: SIDECAR_INBOUND # will match with the inbound listener for app-name:80
        listenerProtocol: HTTP
      filterName: envoy.lua
      filterType: HTTP
      filterConfig:
        inlineCode: |
            function envoy_on_request(request_handle)
                dynamic_metadata = request_handle:streamInfo():dynamicMetadata()

                request_path = request_handle:headers():get(":path")
                if request_path ~= nil then
                    dynamic_metadata:set("envoy.lua", "request_path", request_path)
                else
                    dynamic_metadata:set("envoy.lua", "request_path", '')
                end
            end

            function envoy_on_response(response_handle)
                dynamic_metadata = response_handle:streamInfo():dynamicMetadata()

                local function has_value (arr, val)
                    for index, value in ipairs(arr) do
                        if value == val then
                            return true
                        end
                    end
                    return false
                end

                local function set_cache_control_header(arr, value)
                    if has_value(arr, value)
                    then
                        response_handle:headers():add("Cache-Control", "max-age=604800, public")
                    end
                end

                local extensions = {'css', 'scss', 'js', 'cur', 'jpg', 'jpeg', 'gif', 'htc', 'ico', 'png', 'otf', 'ttf', 'eot', 'woff', 'woff2', 'svg'}

                local request_path = dynamic_metadata:get("envoy.lua")["request_path"]
                for last_part in string.gmatch(request_path, "[^.]+$") do
                    if last_part:match("(.-)?") then
                        for normalized in last_part:gmatch("(.-)?") do
                            set_cache_control_header(extensions, normalized)
                        end
                    else
                        set_cache_control_header(extensions, last_part)
                    end
                end
            end