Adds elasticsearch to the user and channel autocompletion functions (#10354)

* Adds elasticsearch to the user and channel autocompletion functions

* Implement channel store GetChannelsByIds test

* Style changes and govet fixes

* Add gofmt fixes

* Extract default channel search limit to a const

* Add StringSliceDiff function to the utils package

* Honor USER_SEARCH_MAX_LIMIT on the user autocomplete api handler

* Change the elasticsearch development image

store/sqlstore/channel_store.go

@@ -785,10 +785,10 @@ func (s SqlChannelStore) SetDeleteAt(channelId string, deleteAt, updateAt int64)
 		// Additionally propagate the write to the PublicChannels table.
 		if _, err := transaction.Exec(`
 			UPDATE
-			    PublicChannels 
-			SET 
+			    PublicChannels
+			SET
 			    DeleteAt = :DeleteAt
-			WHERE 
+			WHERE
 			    Id = :ChannelId
 		`, map[string]interface{}{
 			"DeleteAt":  deleteAt,
@@ -835,7 +835,7 @@ func (s SqlChannelStore) PermanentDeleteByTeam(teamId string) store.StoreChannel
 		// Additionally propagate the deletions to the PublicChannels table.
 		if _, err := transaction.Exec(`
 			DELETE FROM
-			    PublicChannels 
+			    PublicChannels
 			WHERE
 			    TeamId = :TeamId
 		`, map[string]interface{}{
@@ -881,7 +881,7 @@ func (s SqlChannelStore) PermanentDelete(channelId string) store.StoreChannel {
 		// Additionally propagate the deletion to the PublicChannels table.
 		if _, err := transaction.Exec(`
 			DELETE FROM
-			    PublicChannels 
+			    PublicChannels
 			WHERE
 			    Id = :ChannelId
 		`, map[string]interface{}{
@@ -1689,7 +1689,7 @@ func (s SqlChannelStore) RemoveAllDeactivatedMembers(channelId string) store.Sto
 			DELETE
 			FROM
 				ChannelMembers
-			WHERE 
+			WHERE
 				UserId IN (
 					SELECT
 						Id
@@ -1838,6 +1838,24 @@ func (s SqlChannelStore) GetAll(teamId string) store.StoreChannel {
 	})
 }
 
+func (s SqlChannelStore) GetChannelsByIds(channelIds []string) store.StoreChannel {
+	return store.Do(func(result *store.StoreResult) {
+		keys, params := MapStringsToQueryParams(channelIds, "Channel")
+
+		query := `SELECT * FROM Channels WHERE Id IN ` + keys + ` ORDER BY Name`
+
+		var channels []*model.Channel
+		_, err := s.GetReplica().Select(&channels, query, params)
+
+		if err != nil {
+			mlog.Error(fmt.Sprint(err))
+			result.Err = model.NewAppError("SqlChannelStore.GetChannelsByIds", "store.sql_channel.get_channels_by_ids.app_error", nil, "", http.StatusInternalServerError)
+		} else {
+			result.Data = channels
+		}
+	})
+}
+
 func (s SqlChannelStore) GetForPost(postId string) store.StoreChannel {
 	return store.Do(func(result *store.StoreResult) {
 		channel := &model.Channel{}
@@ -1942,8 +1960,7 @@ func (s SqlChannelStore) AutocompleteInTeam(teamId string, term string, includeD
 			    c.TeamId = :TeamId
 			    ` + deleteFilter + `
 			    %v
-			LIMIT 50
-		`
+			LIMIT ` + strconv.Itoa(model.CHANNEL_SEARCH_DEFAULT_LIMIT)
 
 		var channels model.ChannelList