MM-8678: add CUD support for channel members via plugins (#8565)

* add CUD support for channel members via plugins

This effectively exposes AddChannelMember, UpdateChannelMemberRoles,
UpdateChannelMemberNotifyProps and LeaveChannel via the plugin API.

It also modifies the semantics of AddChannelMember to explicitly allow
for an empty user requestor, left as such for now via the plugin API.

* change the signature of AddChannelMember to accept a channel id instead of a channel

app/channel_test.go

@@ -340,3 +340,44 @@ func TestRemoveUserFromChannelUpdatesChannelMemberHistoryRecord(t *testing.T) {
 	assert.Equal(t, publicChannel.Id, histories[0].ChannelId)
 	assert.NotNil(t, histories[0].LeaveTime)
 }
+
+func TestAddChannelMemberNoUserRequestor(t *testing.T) {
+	th := Setup().InitBasic()
+	defer th.TearDown()
+
+	// create a user and add it to a channel
+	user := th.CreateUser()
+	if _, err := th.App.AddTeamMember(th.BasicTeam.Id, user.Id); err != nil {
+		t.Fatal("Failed to add user to team. Error: " + err.Message)
+	}
+
+	groupUserIds := make([]string, 0)
+	groupUserIds = append(groupUserIds, th.BasicUser.Id)
+	groupUserIds = append(groupUserIds, user.Id)
+
+	channel := th.createChannel(th.BasicTeam, model.CHANNEL_OPEN)
+	userRequestorId := ""
+	postRootId := ""
+	if _, err := th.App.AddChannelMember(user.Id, channel, userRequestorId, postRootId); err != nil {
+		t.Fatal("Failed to add user to channel. Error: " + err.Message)
+	}
+
+	// there should be a ChannelMemberHistory record for the user
+	histories := store.Must(th.App.Srv.Store.ChannelMemberHistory().GetUsersInChannelDuring(model.GetMillis()-100, model.GetMillis()+100, channel.Id)).([]*model.ChannelMemberHistoryResult)
+	assert.Len(t, histories, 2)
+	channelMemberHistoryUserIds := make([]string, 0)
+	for _, history := range histories {
+		assert.Equal(t, channel.Id, history.ChannelId)
+		channelMemberHistoryUserIds = append(channelMemberHistoryUserIds, history.UserId)
+	}
+	assert.Equal(t, groupUserIds, channelMemberHistoryUserIds)
+
+	postList := store.Must(th.App.Srv.Store.Post().GetPosts(channel.Id, 0, 1, false)).(*model.PostList)
+	if assert.Len(t, postList.Order, 1) {
+		post := postList.Posts[postList.Order[0]]
+
+		assert.Equal(t, model.POST_JOIN_CHANNEL, post.Type)
+		assert.Equal(t, user.Id, post.UserId)
+		assert.Equal(t, user.Username, post.Props["username"])
+	}
+}