I am interacting with an http client API which accepts a *tls.Conn. I cannot change the API. I want some code to be executed when the connection is closed, but I don't see a way to do this. If I create a struct which embeds a *tls.Conn and I "override" Close(), the API won't accept the struct because go only follows the sub-type is-a relationship with interfaces - tls.Conn is not an interface.
Is there any way to get around this - is there some standard hook I can use to be notified when the client connection is closed?
If you're using tls.Client to construct the *tls.Conn then you can wrap the first argument to achieve your goal.
type CloseListener struct {
net.Conn // embed the original conn
}
func (c *CloseListener) Close() error {
err := c.Conn.Close()
// ... do your stuff ...
return err
}
conn := tls.Client(&CloseListener{c}, &tls.Config{ /* ... */ })
If you look at how tls.Conn's Close is implemented you'll see that it should call your Close implementation unless there was some error.