Move WriteFlusher out of utils into ioutils

Signed-off-by: Andrew "Tianon" Page <admwiggin@gmail.com>

ioutils/writeflusher.go

@@ -0,0 +1,47 @@
+package ioutils
+
+import (
+	"io"
+	"net/http"
+	"sync"
+)
+
+type WriteFlusher struct {
+	sync.Mutex
+	w       io.Writer
+	flusher http.Flusher
+	flushed bool
+}
+
+func (wf *WriteFlusher) Write(b []byte) (n int, err error) {
+	wf.Lock()
+	defer wf.Unlock()
+	n, err = wf.w.Write(b)
+	wf.flushed = true
+	wf.flusher.Flush()
+	return n, err
+}
+
+// Flush the stream immediately.
+func (wf *WriteFlusher) Flush() {
+	wf.Lock()
+	defer wf.Unlock()
+	wf.flushed = true
+	wf.flusher.Flush()
+}
+
+func (wf *WriteFlusher) Flushed() bool {
+	wf.Lock()
+	defer wf.Unlock()
+	return wf.flushed
+}
+
+func NewWriteFlusher(w io.Writer) *WriteFlusher {
+	var flusher http.Flusher
+	if f, ok := w.(http.Flusher); ok {
+		flusher = f
+	} else {
+		flusher = &NopFlusher{}
+	}
+	return &WriteFlusher{w: w, flusher: flusher}
+}