[PLT-7362] Add post' root ID to APIv4 addChannelMember to render added user (as system post) at RHS (#7730)

* add post' root ID to apiv4 addChannelMember to render added user (as system post) at RHS

* add check to post_root_id parameter

* add AddChannelMemberWithRootId function for backward compatibility

5 files changed, 59 insertions, 14 deletions

diff --git a/api/channel.go b/api/channel.go
index f41a588ee..2782f9636 100644
--- a/api/channel.go
+++ b/api/channel.go
@@ -649,7 +649,7 @@ func addMember(c *Context, w http.ResponseWriter, r *http.Request) {
 	}
 
 	c.App.Go(func() {
-		c.App.PostAddToChannelMessage(oUser, nUser, channel)
+		c.App.PostAddToChannelMessage(oUser, nUser, channel, "")
 	})
 
 	c.App.UpdateChannelLastViewedAt([]string{id}, oUser.Id)
diff --git a/api4/channel.go b/api4/channel.go
index 5a3920a0a..f96942a4f 100644
--- a/api4/channel.go
+++ b/api4/channel.go
@@ -783,21 +783,36 @@ func addChannelMember(c *Context, w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	member := model.ChannelMemberFromJson(r.Body)
-	if member == nil {
-		c.SetInvalidParam("channel_member")
+	props := model.StringInterfaceFromJson(r.Body)
+	userId, ok := props["user_id"].(string)
+	if !ok || len(userId) != 26 {
+		c.SetInvalidParam("user_id")
 		return
 	}
 
-	if len(member.UserId) != 26 {
-		c.SetInvalidParam("user_id")
+	member := &model.ChannelMember{
+		ChannelId: c.Params.ChannelId,
+		UserId:    userId,
+	}
+
+	postRootId, ok := props["post_root_id"].(string)
+	if ok && len(postRootId) != 0 && len(postRootId) != 26 {
+		c.SetInvalidParam("post_root_id")
 		return
 	}
 
-	member.ChannelId = c.Params.ChannelId
+	var err *model.AppError
+	if ok && len(postRootId) == 26 {
+		if rootPost, err := c.App.GetSinglePost(postRootId); err != nil {
+			c.Err = err
+			return
+		} else if rootPost.ChannelId != member.ChannelId {
+			c.SetInvalidParam("post_root_id")
+			return
+		}
+	}
 
 	var channel *model.Channel
-	var err *model.AppError
 	if channel, err = c.App.GetChannel(member.ChannelId); err != nil {
 		c.Err = err
 		return
@@ -828,7 +843,7 @@ func addChannelMember(c *Context, w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	if cm, err := c.App.AddChannelMember(member.UserId, channel, c.Session.UserId); err != nil {
+	if cm, err := c.App.AddChannelMember(member.UserId, channel, c.Session.UserId, postRootId); err != nil {
 		c.Err = err
 		return
 	} else {
diff --git a/api4/channel_test.go b/api4/channel_test.go
index af47aca95..d341837c8 100644
--- a/api4/channel_test.go
+++ b/api4/channel_test.go
@@ -1740,6 +1740,24 @@ func TestAddChannelMember(t *testing.T) {
 		t.Fatal("should have returned exact user added to private channel")
 	}
 
+	post := &model.Post{ChannelId: publicChannel.Id, Message: "a" + GenerateTestId() + "a"}
+	rpost, err := Client.CreatePost(post)
+	if err == nil {
+		t.Fatal("should have created a post")
+	}
+
+	Client.RemoveUserFromChannel(publicChannel.Id, user.Id)
+	_, resp = Client.AddChannelMemberWithRootId(publicChannel.Id, user.Id, rpost.Id)
+	CheckNoError(t, resp)
+	CheckCreatedStatus(t, resp)
+
+	Client.RemoveUserFromChannel(publicChannel.Id, user.Id)
+	_, resp = Client.AddChannelMemberWithRootId(publicChannel.Id, user.Id, "junk")
+	CheckBadRequestStatus(t, resp)
+
+	_, resp = Client.AddChannelMemberWithRootId(publicChannel.Id, user.Id, GenerateTestId())
+	CheckNotFoundStatus(t, resp)
+
 	Client.RemoveUserFromChannel(publicChannel.Id, user.Id)
 	_, resp = Client.AddChannelMember(publicChannel.Id, user.Id)
 	CheckNoError(t, resp)
diff --git a/app/channel.go b/app/channel.go
index 465f2cc80..4ccc12004 100644
--- a/app/channel.go
+++ b/app/channel.go
@@ -61,7 +61,7 @@ func (a *App) JoinDefaultChannels(teamId string, user *model.User, channelRole s
 				l4g.Error(utils.T("api.channel.post_user_add_remove_message_and_forget.error"), err)
 			}
 		} else {
-			if err := a.PostAddToChannelMessage(requestor, user, townSquare); err != nil {
+			if err := a.PostAddToChannelMessage(requestor, user, townSquare, ""); err != nil {
 				l4g.Error(utils.T("api.channel.post_user_add_remove_message_and_forget.error"), err)
 			}
 		}
@@ -86,7 +86,7 @@ func (a *App) JoinDefaultChannels(teamId string, user *model.User, channelRole s
 				l4g.Error(utils.T("api.channel.post_user_add_remove_message_and_forget.error"), err)
 			}
 		} else {
-			if err := a.PostAddToChannelMessage(requestor, user, offTopic); err != nil {
+			if err := a.PostAddToChannelMessage(requestor, user, offTopic, ""); err != nil {
 				l4g.Error(utils.T("api.channel.post_user_add_remove_message_and_forget.error"), err)
 			}
 		}
@@ -555,7 +555,7 @@ func (a *App) AddUserToChannel(user *model.User, channel *model.Channel) (*model
 	return newMember, nil
 }
 
-func (a *App) AddChannelMember(userId string, channel *model.Channel, userRequestorId string) (*model.ChannelMember, *model.AppError) {
+func (a *App) AddChannelMember(userId string, channel *model.Channel, userRequestorId string, postRootId string) (*model.ChannelMember, *model.AppError) {
 	if result := <-a.Srv.Store.Channel().GetMember(channel.Id, userId); result.Err != nil {
 		if result.Err.Id != store.MISSING_CHANNEL_MEMBER_ERROR {
 			return nil, result.Err
@@ -585,7 +585,7 @@ func (a *App) AddChannelMember(userId string, channel *model.Channel, userReques
 		a.postJoinChannelMessage(user, channel)
 	} else {
 		a.Go(func() {
-			a.PostAddToChannelMessage(userRequestor, user, channel)
+			a.PostAddToChannelMessage(userRequestor, user, channel, postRootId)
 		})
 	}
 
@@ -986,12 +986,13 @@ func (a *App) postLeaveChannelMessage(user *model.User, channel *model.Channel)
 	return nil
 }
 
-func (a *App) PostAddToChannelMessage(user *model.User, addedUser *model.User, channel *model.Channel) *model.AppError {
+func (a *App) PostAddToChannelMessage(user *model.User, addedUser *model.User, channel *model.Channel, postRootId string) *model.AppError {
 	post := &model.Post{
 		ChannelId: channel.Id,
 		Message:   fmt.Sprintf(utils.T("api.channel.add_member.added"), addedUser.Username, user.Username),
 		Type:      model.POST_ADD_TO_CHANNEL,
 		UserId:    user.Id,
+		RootId:    postRootId,
 		Props: model.StringInterface{
 			"username":      user.Username,
 			"addedUsername": addedUser.Username,
diff --git a/model/client4.go b/model/client4.go
index bcd41638b..916e9d6de 100644
--- a/model/client4.go
+++ b/model/client4.go
@@ -1663,6 +1663,17 @@ func (c *Client4) AddChannelMember(channelId, userId string) (*ChannelMember, *R
 	}
 }
 
+// AddChannelMemberWithRootId adds user to channel and return a channel member. Post add to channel message has the postRootId.
+func (c *Client4) AddChannelMemberWithRootId(channelId, userId, postRootId string) (*ChannelMember, *Response) {
+	requestBody := map[string]string{"user_id": userId, "post_root_id": postRootId}
+	if r, err := c.DoApiPost(c.GetChannelMembersRoute(channelId)+"", MapToJson(requestBody)); err != nil {
+		return nil, BuildErrorResponse(r, err)
+	} else {
+		defer closeBody(r)
+		return ChannelMemberFromJson(r.Body), BuildResponse(r)
+	}
+}
+
 // RemoveUserFromChannel will delete the channel member object for a user, effectively removing the user from a channel.
 func (c *Client4) RemoveUserFromChannel(channelId, userId string) (bool, *Response) {
 	if r, err := c.DoApiDelete(c.GetChannelMemberRoute(channelId, userId)); err != nil {