MM-11210 Add "GET /posts/unread" API to support landing on the last unread post (#11486)

* [MM-11210] Add API GET 'api/v4/channels/{channel_id:[A-Za-z0-9]+}/posts/unread' for scrolling overhaul (#9108)

* Add API GET 'api/v4/channels/{channel_id:[A-Za-z0-9]+}/posts/unread'

* add constants

* refactor GetPostSince and added more tests

* move constants to app package

* [MM-11528 &&  MM-11583] Add userId to in the "posts/unread" path and update test with time delay to fix intermittent failure (#9229)

* add userId to in the "posts/unread" path and update test with time delay to fix intermittent failure

* add limit before and after to query

* remove time delay on test and put pretermined value of Post.CreateAt

* Fix conflict

* [MM-11876] Add cursor to posts list such as next_post_id and previous_post_id (#9707)

* add cursor to posts list such as next_post_id and previous_post_id

add publish previous_post_id on WEBSOCKET_EVENT_POSTED and only get next or previous post IDs if necessary

revert change on adding previous_post_id in WEBSOCKET_EVENT_POSTED

add missing strings import

fix merge conflicts

* update per comment

* update per feedback

* corrected the logic in getting the next and previous post ID

* fix logic to determine next and post IDs, and rename function to have suffix of "Time"

* rearrange logics and add mote tests

* fix merge conflict

* fix missing message when using unread API (#10233)

* MM-15569 Fixes failing test on TestGetPostsForChannelAroundLastUnread (#11039)

* Fix missing posts when getting posts since

* revert changes to GetPostsSince

* migrate Post.GetPostAfterTime and Post.GetPostBeforeTime to sync by default

* revert change to cacheItem

* Fix post ID validation, build query on squirrel and only return post ID as necessary

web/params.go

@@ -18,6 +18,8 @@ const (
 	PER_PAGE_MAXIMUM      = 200
 	LOGS_PER_PAGE_DEFAULT = 10000
 	LOGS_PER_PAGE_MAXIMUM = 10000
+	LIMIT_DEFAULT         = 60
+	LIMIT_MAXIMUM         = 200
 )
 
 type Params struct {
@@ -68,6 +70,8 @@ type Params struct {
 	IncludeMemberCount     bool
 	NotAssociatedToGroup   string
 	ExcludeDefaultChannels bool
+	LimitAfter             int
+	LimitBefore            int
 	GroupIDs               string
 	IncludeTotalCount      bool
 }
@@ -226,6 +230,22 @@ func ParamsFromRequest(r *http.Request) *Params {
 		params.LogsPerPage = val
 	}
 
+	if val, err := strconv.Atoi(query.Get("limit_after")); err != nil || val < 0 {
+		params.LimitAfter = LIMIT_DEFAULT
+	} else if val > LIMIT_MAXIMUM {
+		params.LimitAfter = LIMIT_MAXIMUM
+	} else {
+		params.LimitAfter = val
+	}
+
+	if val, err := strconv.Atoi(query.Get("limit_before")); err != nil || val < 0 {
+		params.LimitBefore = LIMIT_DEFAULT
+	} else if val > LIMIT_MAXIMUM {
+		params.LimitBefore = LIMIT_MAXIMUM
+	} else {
+		params.LimitBefore = val
+	}
+
 	if val, ok := props["syncable_id"]; ok {
 		params.SyncableId = val
 	}