elasticsearch: set _type=doc (#3757)

The `_type` field is deprecated per
elastic/elasticsearch#15613

CHANGELOG.asciidoc

@@ -17,6 +17,7 @@ https://github.com/elastic/beats/compare/v5.1.1...master[Check the HEAD diff]
 - Change beat generator. Use `$GOPATH/src/github.com/elastic/beats/script/generate.py` to generate a beat. {pull}3452[3452]
 - Configuration files must be owned by the user running the beat or by root, and
   they must not be writable by others. {pull}3544[3544] {pull}3689[3689]
+- Usage of field `_type` is now ignored and hardcoded to `doc`. {pull}3757[3757]
 
 *Filebeat*
 - Always use absolute path for event and registry. This can lead to issues when relative paths were used before. {pull}3328[3328]

libbeat/outputs/elasticsearch/client.go

@@ -96,6 +96,10 @@ var (
 	errExcpectedObjectEnd    = errors.New("expected end of object")
 )
 
+const (
+	eventType = "doc"
+)
+
 // NewClient instantiates a new client.
 func NewClient(
 	s ClientSettings,
@@ -328,7 +332,7 @@ func createEventBulkMeta(
 		return bulkMeta{
 			Index: bulkMetaIndex{
 				Index:   getIndex(event, index),
-				DocType: event["type"].(string),
+				DocType: eventType,
 			},
 		}
 	}
@@ -346,7 +350,7 @@ func createEventBulkMeta(
 		Index: bulkMetaIndex{
 			Index:    getIndex(event, index),
 			Pipeline: pipeline,
-			DocType:  event["type"].(string),
+			DocType:  eventType,
 		},
 	}
 }
@@ -548,7 +552,6 @@ func (client *Client) PublishEvent(data outputs.Data) error {
 
 	event := data.Event
 	index := getIndex(event, client.index)
-	typ := event["type"].(string)
 
 	debugf("Publish event: %s", event)
 
@@ -562,9 +565,9 @@ func (client *Client) PublishEvent(data outputs.Data) error {
 
 	var status int
 	if pipeline == "" {
-		status, _, err = client.Index(index, typ, "", client.params, event)
+		status, _, err = client.Index(index, eventType, "", client.params, event)
 	} else {
-		status, _, err = client.Ingest(index, typ, pipeline, "", client.params, event)
+		status, _, err = client.Ingest(index, eventType, pipeline, "", client.params, event)
 	}
 
 	// check indexing error