go/src/crypto/cipher/io.go

type StreamReader …

func (r StreamReader) Read(dst []byte) (n int, err error) { … }

type StreamWriter …

func (w StreamWriter) Write(src []byte) (n int, err error) { … }

// Close closes the underlying Writer and returns its Close return value, if the Writer
// is also an io.Closer. Otherwise it returns nil.
func (w StreamWriter) Close() error { … }