Dave Cheney on bridging from one Golang interface to another:
The value returned by io.MultiWriter is an implementation of io.Writer, it doesn’t have the rest of the methods necessary to fulfil the net.Conn interface; what I really need is the ability to replace the Write method of an existing net.Conn value. We can do this with embedding by creating a structure that embeds both a net.Conn and an independant io.Writer as anonymous fields.