Mapper-attachments

Elastic Stack Elasticsearch
4

Very wired here.

here is my env:

http://localhost:9200/_nodes/plugins?pretty

{
  "cluster_name" : "elasticsearch",
  "nodes" : {
    "hYCvRc1yQSK3BoClf5C5zQ" : {
      "name" : "Destroyer of Demons",
      "transport_address" : "127.0.0.1:9300",
      "host" : "127.0.0.1",
      "ip" : "127.0.0.1",
      "version" : "**2.3.1"**,
      "build" : "bd98092",
      "http_address" : "127.0.0.1:9200",
      "plugins" : [ {
        "name" : "**mapper-attachments**",
        "version" : **"2.3.1",**
        ...
      } ],

mapping is:

"tech": {
    "mappings": {
      "manual": {
        "properties": {
          "file": {
            "type": "attachment",
            "fields": {
              "content": {
                "type": "string"
              },
              "author": {
                "type": "string"
              },
              "**title**": {
                "type": "string",
                "store": true
              },
              "**name**": {
                "type": "string"
              },
              "date": {
                "type": "string",
                "store": true
              },
              "**keywords**": {
                "type": "string",
                "store": true
              },
              "**content_type**": {
                "type": "string",
                "store": true
              },
              "content_length": {
                "type": "string",
                "store": true
              },
              "**language**": {
                "type": "string",
                "store": true
              }
            }
          }
        }
      }

I am able to see the content of the indexed document:

   "_source": {
      "file": {
        "_content": "JVBERi0xLjcNJeLjz9MNCg==M......=ZW5kc3RyZWFtDWVuZG9iag1zdGFydHhyZWYNCg==MTE2DQo=JSVFT0YNCg=="
        "_name": "12-240.pdf",
        "_title": "12-240.pdf",
        "_keywords": "Div42 Src580 LGE Mechtech",
        "_language": "en",
        "_content_type": "pdf"
}

but when I search

curl -XGET "http://localhost:9200/tech/manual/_search" -d'
{
  "fields": ["file.content_type", "file.title", "file.keywords", "file.language", "file.name"], 
  "query": {
   "match_all": {}
  }
}'

the response has no file.keywords, file.language, and file.name as follow, I also can't search on these fields.

 "hits": {
    "total": 1,
    "max_score": 0.30685282,
    "hits": [
      {
        "_index": "tech",
        "_type": "manual",
        "_id": "AVPx8cRH4bGZ_KKaUS0y",
        "_score": 0.30685282,
        "fields": {
          "file.content_type": [
            "pdf"
          ],
          "file.title": [
            "12-240"
          ]
        }
      }
    ]
  }

what's possible not right?
Thanks!