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

model/client4.go

@@ -2509,6 +2509,17 @@ func (c *Client4) GetPostsBefore(channelId, postId string, page, perPage int, et
 	return PostListFromJson(r.Body), BuildResponse(r)
 }
 
+// GetPostsAroundLastUnread gets a list of posts around last unread post by a user in a channel.
+func (c *Client4) GetPostsAroundLastUnread(userId, channelId string, limitBefore, limitAfter int) (*PostList, *Response) {
+	query := fmt.Sprintf("?limit_before=%v&limit_after=%v", limitBefore, limitAfter)
+	if r, err := c.DoApiGet(c.GetUserRoute(userId)+c.GetChannelRoute(channelId)+"/posts/unread"+query, ""); err != nil {
+		return nil, BuildErrorResponse(r, err)
+	} else {
+		defer closeBody(r)
+		return PostListFromJson(r.Body), BuildResponse(r)
+	}
+}
+
 // SearchPosts returns any posts with matching terms string.
 func (c *Client4) SearchPosts(teamId string, terms string, isOrSearch bool) (*PostList, *Response) {
 	params := SearchParameter{

model/post_list.go

@@ -10,14 +10,18 @@ import (
 )
 
 type PostList struct {
-	Order []string         `json:"order"`
-	Posts map[string]*Post `json:"posts"`
+	Order      []string         `json:"order"`
+	Posts      map[string]*Post `json:"posts"`
+	NextPostId string           `json:"next_post_id"`
+	PrevPostId string           `json:"prev_post_id"`
 }
 
 func NewPostList() *PostList {
 	return &PostList{
-		Order: make([]string, 0),
-		Posts: make(map[string]*Post),
+		Order:      make([]string, 0),
+		Posts:      make(map[string]*Post),
+		NextPostId: "",
+		PrevPostId: "",
 	}
 }