Can not get x-b3-* tracing headers in EnvoyFilter

Hi, I’m using 1.1.4 and have an EnvoyFilter:

    apiVersion: networking.istio.io/v1alpha3
    kind: EnvoyFilter
    metadata:
      name: auth-debug
    spec:
      workloadLabels:
        app: istio-ingressgateway
      filters:
      - listenerMatch:
          portNumber: 443
          listenerType: GATEWAY
        filterName: envoy.lua
        filterType: HTTP
        insertPosition:
          index: FIRST
        filterConfig:
          inlineCode: |
            function envoy_on_request(request_handle)
                for key, value in pairs(request_handle:headers()) do
                   request_handle:logWarn("key:" .. key .. " <--> value:" .. value)
                end
            end

            function envoy_on_response(response_handle)
            end

And I define access log format "---> [%START_TIME%] %REQ(:METHOD)% %REQ(X-ENVOY-ORIGINAL-PATH?:PATH)% %PROTOCOL% %REQ(X-REQUEST-ID)% %REQ(X-B3-TRACEID)% %REQ(X-B3-SPANID)% %REQ(X-B3-PARENTSPANID)% %REQ(XRING)%\n"

Then I have curl https://foo.bar.com/book/booklist and get ingress gateway access log:

[2019-06-02 09:36:18.988][228][warning][lua] [external/envoy/source/extensions/filters/http/lua/lua_filter.cc:538] script log: key::method <--> value:GET
[2019-06-02 09:36:18.988][228][warning][lua] [external/envoy/source/extensions/filters/http/lua/lua_filter.cc:538] script log: key::path <--> value:/book/booklist
[2019-06-02 09:36:18.988][228][warning][lua] [external/envoy/source/extensions/filters/http/lua/lua_filter.cc:538] script log: key::scheme <--> value:https
[2019-06-02 09:36:18.988][228][warning][lua] [external/envoy/source/extensions/filters/http/lua/lua_filter.cc:538] script log: key::authority <--> value:foo.bar.com
[2019-06-02 09:36:18.988][228][warning][lua] [external/envoy/source/extensions/filters/http/lua/lua_filter.cc:538] script log: key:user-agent <--> value:curl/7.54.0
[2019-06-02 09:36:18.988][228][warning][lua] [external/envoy/source/extensions/filters/http/lua/lua_filter.cc:538] script log: key:accept <--> value:*/*
[2019-06-02 09:36:18.988][228][warning][lua] [external/envoy/source/extensions/filters/http/lua/lua_filter.cc:538] script log: key:x-forwarded-for <--> value:192.168.0.136
[2019-06-02 09:36:18.988][228][warning][lua] [external/envoy/source/extensions/filters/http/lua/lua_filter.cc:538] script log: key:x-forwarded-proto <--> value:https
[2019-06-02 09:36:18.988][228][warning][lua] [external/envoy/source/extensions/filters/http/lua/lua_filter.cc:538] script log: key:x-envoy-internal <--> value:true
[2019-06-02 09:36:18.988][228][warning][lua] [external/envoy/source/extensions/filters/http/lua/lua_filter.cc:538] script log: key:x-request-id <--> value:9dcbfa89-993b-93d3-92f7-954c7b4da6a8
[2019-06-02 09:36:18.988][228][warning][lua] [external/envoy/source/extensions/filters/http/lua/lua_filter.cc:538] script log: key:x-envoy-decorator-operation <--> value:seed-gateway.x.svc.cluster.local:80/book/*
[2019-06-02 09:36:18.988][228][warning][lua] [external/envoy/source/extensions/filters/http/lua/lua_filter.cc:538] script log: before key::method <--> before value:GET
[2019-06-02 09:36:18.988][228][warning][lua] [external/envoy/source/extensions/filters/http/lua/lua_filter.cc:538] script log: before key::path <--> before value:/book/booklist
[2019-06-02 09:36:18.988][228][warning][lua] [external/envoy/source/extensions/filters/http/lua/lua_filter.cc:538] script log: before key::scheme <--> before value:https
[2019-06-02 09:36:18.988][228][warning][lua] [external/envoy/source/extensions/filters/http/lua/lua_filter.cc:538] script log: before key::authority <--> before value:api-x.yjyz.com
[2019-06-02 09:36:18.988][228][warning][lua] [external/envoy/source/extensions/filters/http/lua/lua_filter.cc:538] script log: before key:user-agent <--> before value:curl/7.54.0
[2019-06-02 09:36:18.988][228][warning][lua] [external/envoy/source/extensions/filters/http/lua/lua_filter.cc:538] script log: before key:accept <--> before value:*/*
[2019-06-02 09:36:18.988][228][warning][lua] [external/envoy/source/extensions/filters/http/lua/lua_filter.cc:538] script log: before key:x-forwarded-for <--> before value:192.168.0.136
[2019-06-02 09:36:18.988][228][warning][lua] [external/envoy/source/extensions/filters/http/lua/lua_filter.cc:538] script log: before key:x-forwarded-proto <--> before value:https
[2019-06-02 09:36:18.988][228][warning][lua] [external/envoy/source/extensions/filters/http/lua/lua_filter.cc:538] script log: before key:x-envoy-internal <--> before value:true
[2019-06-02 09:36:18.988][228][warning][lua] [external/envoy/source/extensions/filters/http/lua/lua_filter.cc:538] script log: before key:x-request-id <--> before value:9dcbfa89-993b-93d3-92f7-954c7b4da6a8
[2019-06-02 09:36:18.988][228][warning][lua] [external/envoy/source/extensions/filters/http/lua/lua_filter.cc:538] script log: before key:x-envoy-decorator-operation <--> before value:seed-gateway.x.svc.cluster.local:80/book/*
[2019-06-02 09:36:18.988][228][warning][lua] [external/envoy/source/extensions/filters/http/lua/lua_filter.cc:538] script log: before key:x-istio-attributes <--> before value:CiQKHWRlc3RpbmF0aW9uLnNlcnZpY2UubmFtZXNwYWNlEgMSAXgKKgoYZGVzdGluYXRpb24uc2VydmljZS5uYW1lEg4SDHNlZWQtZ2F0ZXdheQpPCgpzb3VyY2UudWlkEkESP2t1YmVybmV0ZXM6Ly9pc3Rpby1pbmdyZXNzZ2F0ZXdheS02NWRiOTY0NmQ0LXNqaGM5LmlzdGlvLXN5c3RlbQo8ChdkZXN0aW5hdGlvbi5zZXJ2aWNlLnVpZBIhEh9pc3RpbzovL3gvc2VydmljZXMvc2VlZC1nYXRld2F5Cj4KGGRlc3RpbmF0aW9uLnNlcnZpY2UuaG9zdBIiEiBzZWVkLWdhdGV3YXkueC5zdmMuY2x1c3Rlci5sb2NhbA==
---> [2019-06-02T09:36:18.987Z] GET /book/booklist HTTP/2 9dcbfa89-993b-93d3-92f7-954c7b4da6a8 dab6bcd36d862c1871547a5ff8134aef 71547a5ff8134aef - -

Why I can not get traceid and spanid with value dab6bcd36d862c1871547a5ff8134aef and 71547a5ff8134aef from the for loop in Lua script?