Yea I saw your other reply later and agree on most of it. But I'd say there's a balance between simplicity of the API and more specific cases. For example they can make an optional api to io.Reader to provide size info, and maybe another optional api to io.Reader to make it able to be read more than once, etc.. But at the same time, if you have all those info, that _usually_ means you already have either a []byte or string, and you would most likely use one of the 3 types to convert that into an io.Reader, so that special handling is enough without adding more public apis, and the go team is notoriously conservative when adding new public apis.