kubernetes/staging/src/k8s.io/apiserver/pkg/util/flushwriter/writer.go

// Wrap wraps an io.Writer into a writer that flushes after every write if
// the writer implements the Flusher interface.
func Wrap(w io.Writer) io.Writer { … }

type flushWriter …

// Write is a FlushWriter implementation of the io.Writer that sends any buffered
// data to the client.
func (fw *flushWriter) Write(p []byte) (n int, err error) { … }