MM-27493 Shared channels (MVP) (#17301)

Remote Cluster Service
- provides ability for multiple Mattermost cluster instances to create a trusted connection with each other and exchange messages
- trusted connections are managed via slash commands (for now)
- facilitates features requiring inter-cluster communication, such as Shared Channels
Shared Channels Service
- provides ability to shared channels between one or more Mattermost cluster instances (using trusted connection)
- sharing/unsharing of channels is managed via slash commands (for now)

app/post_test.go

@@ -2053,3 +2053,87 @@ func TestReplyToPostWithLag(t *testing.T) {
 		require.NotNil(t, reply)
 	})
 }
+
+func TestSharedChannelSyncForPostActions(t *testing.T) {
+	t.Run("creating a post in a shared channel performs a content sync when sync service is running on that node", func(t *testing.T) {
+		th := Setup(t).InitBasic()
+		defer th.TearDown()
+
+		remoteClusterService := NewMockSharedChannelService(nil)
+		th.App.srv.sharedChannelService = remoteClusterService
+		testCluster := &testlib.FakeClusterInterface{}
+		th.Server.Cluster = testCluster
+
+		user := th.BasicUser
+
+		channel := th.CreateChannel(th.BasicTeam, WithShared(true))
+
+		_, err := th.App.CreatePost(&model.Post{
+			UserId:    user.Id,
+			ChannelId: channel.Id,
+			Message:   "Hello folks",
+		}, channel, false, true)
+		require.Nil(t, err, "Creating a post should not error")
+
+		assert.Len(t, remoteClusterService.notifications, 1)
+		assert.Equal(t, channel.Id, remoteClusterService.notifications[0])
+	})
+
+	t.Run("updating a post in a shared channel performs a content sync when sync service is running on that node", func(t *testing.T) {
+		th := Setup(t).InitBasic()
+		defer th.TearDown()
+
+		remoteClusterService := NewMockSharedChannelService(nil)
+		th.App.srv.sharedChannelService = remoteClusterService
+		testCluster := &testlib.FakeClusterInterface{}
+		th.Server.Cluster = testCluster
+
+		user := th.BasicUser
+
+		channel := th.CreateChannel(th.BasicTeam, WithShared(true))
+
+		post, err := th.App.CreatePost(&model.Post{
+			UserId:    user.Id,
+			ChannelId: channel.Id,
+			Message:   "Hello folks",
+		}, channel, false, true)
+		require.Nil(t, err, "Creating a post should not error")
+
+		_, err = th.App.UpdatePost(post, true)
+		require.Nil(t, err, "Updating a post should not error")
+
+		assert.Len(t, remoteClusterService.notifications, 2)
+		assert.Equal(t, channel.Id, remoteClusterService.notifications[0])
+		assert.Equal(t, channel.Id, remoteClusterService.notifications[1])
+	})
+
+	t.Run("deleting a post in a shared channel performs a content sync when sync service is running on that node", func(t *testing.T) {
+		th := Setup(t).InitBasic()
+		defer th.TearDown()
+
+		remoteClusterService := NewMockSharedChannelService(nil)
+		th.App.srv.sharedChannelService = remoteClusterService
+		testCluster := &testlib.FakeClusterInterface{}
+		th.Server.Cluster = testCluster
+
+		user := th.BasicUser
+
+		channel := th.CreateChannel(th.BasicTeam, WithShared(true))
+
+		post, err := th.App.CreatePost(&model.Post{
+			UserId:    user.Id,
+			ChannelId: channel.Id,
+			Message:   "Hello folks",
+		}, channel, false, true)
+		require.Nil(t, err, "Creating a post should not error")
+
+		_, err = th.App.DeletePost(post.Id, user.Id)
+		require.Nil(t, err, "Deleting a post should not error")
+
+		// one creation and two deletes
+		assert.Len(t, remoteClusterService.notifications, 3)
+		assert.Equal(t, channel.Id, remoteClusterService.notifications[0])
+		assert.Equal(t, channel.Id, remoteClusterService.notifications[1])
+		assert.Equal(t, channel.Id, remoteClusterService.notifications[2])
+	})
+}