I have server with several net.Conn. How can I get list of net.Conn which have unreaded messages (without using active waiting) ?
I don't think you can.
If you try to read from the net.Conn with its Read method, it will block until there is data. So just start a goroutine for each net.Conn, and read from it in the goroutine.
The example in the net package's documentation does exactly that: https://golang.org/pkg/net/#example_Listener