How can diff_drive_controller package subscribe to velocity topics?

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I guess my question is not clear enough, sorry about it. TO be more clear, I am using move_base too. It is publishing the cmd_vel. I want to create a closed-loop control system. My hardware interface is reading encoder values and converts it into speed feedbacks. How should I input this feedbacks into diff_drive_controller package?

The encoder values need to be converted to an odometry value and published to odom. I don't know how diff_drive_controller would make use of that as it's only subscribing to cmd_vel.

It is only subscribing to the cmd_vel as you mentioned. Also, it publishes Odom so it should be somehow taken encoder feedback as input. I don't know how to make the encoder feedbacks input to the diff_drive_controller.

Sorry, I couldn't figure it out. But here's the package that I used: http://wiki.ros.org/differential_drive It's more straightforward and the documentation is way better. Hope it helps!