Package encoding provides a number of encodings that are missing from the standard Go [encoding]("https://godoc.org/golang.org/x/text/encoding") package.
We hope that we can contribute these to the standard Go library someday. It turns out that some of these are useful for dealing with I/O streams coming from non-UTF friendly sources.
The UTF8 Encoder is also useful for situations where valid UTF-8 might be carried in streams that contain non-valid UTF; in particular I use it for helping me cope with terminals that embed escape sequences in otherwise valid UTF-8.