Add query parameters to get posts v4 endpoint (#5858)

* Add since query paremeter to get posts v4 endpoint

* Add query paremeters for before/after to get posts v4 endpoint

model/client4.go

@@ -1159,6 +1159,39 @@ func (c *Client4) GetPostsForChannel(channelId string, page, perPage int, etag s
 	}
 }
 
+// GetPostsSince gets posts created after a specified time as Unix time in milliseconds.
+func (c *Client4) GetPostsSince(channelId string, time int64) (*PostList, *Response) {
+	query := fmt.Sprintf("?since=%v", time)
+	if r, err := c.DoApiGet(c.GetChannelRoute(channelId)+"/posts"+query, ""); err != nil {
+		return nil, &Response{StatusCode: r.StatusCode, Error: err}
+	} else {
+		defer closeBody(r)
+		return PostListFromJson(r.Body), BuildResponse(r)
+	}
+}
+
+// GetPostsAfter gets a page of posts that were posted after the post provided.
+func (c *Client4) GetPostsAfter(channelId, postId string, page, perPage int, etag string) (*PostList, *Response) {
+	query := fmt.Sprintf("?page=%v&per_page=%v&after=%v", page, perPage, postId)
+	if r, err := c.DoApiGet(c.GetChannelRoute(channelId)+"/posts"+query, etag); err != nil {
+		return nil, &Response{StatusCode: r.StatusCode, Error: err}
+	} else {
+		defer closeBody(r)
+		return PostListFromJson(r.Body), BuildResponse(r)
+	}
+}
+
+// GetPostsBefore gets a page of posts that were posted before the post provided.
+func (c *Client4) GetPostsBefore(channelId, postId string, page, perPage int, etag string) (*PostList, *Response) {
+	query := fmt.Sprintf("?page=%v&per_page=%v&before=%v", page, perPage, postId)
+	if r, err := c.DoApiGet(c.GetChannelRoute(channelId)+"/posts"+query, etag); err != nil {
+		return nil, &Response{StatusCode: r.StatusCode, Error: 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) {
 	requestBody := map[string]string{"terms": terms, "is_or_search": strconv.FormatBool(isOrSearch)}