List All the field names in an index matching

How do i only list all the field names using the GET API without any extra information.? I don't want it's specific value.

For eg:

curl -XGET 'localhost:9200/metricsindex/_search?scroll=10m&pretty' -d '{ "query": { "filtered": { "query": { "match_all": {} }, "filter": { "range": { "@timestamp": { "gte": "2016-07-05T14:00:00", "lte": "2016-07-07T15:00:00" } } } } } } '

I need to know all the field names(metrics) associated with the index metricsindex within the given time range.

Then drill down to get the value of a particular metric.

You cannot do this, the closest you can get is to use the _mapping API and something like jq.