containerd/progress/writer.go

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package progress
import (
"bytes"
"fmt"
"io"
)
// Writer buffers writes until flush, at which time the last screen is cleared
// and the current buffer contents are written. This is useful for
// implementing progress displays, such as those implemented in docker and
// git.
type Writer struct {
buf bytes.Buffer
w io.Writer
lines int
}
func NewWriter(w io.Writer) *Writer {
return &Writer{
w: w,
}
}
func (w *Writer) Write(p []byte) (n int, err error) {
return w.buf.Write(p)
}
// Flush should be called when refreshing the current display.
func (w *Writer) Flush() error {
if w.buf.Len() == 0 {
return nil
}
if err := w.clear(); err != nil {
return err
}
w.lines = bytes.Count(w.buf.Bytes(), []byte("\n"))
if _, err := w.w.Write(w.buf.Bytes()); err != nil {
return err
}
w.buf.Reset()
return nil
}
// TODO(stevvooe): The following are system specific. Break these out if we
// decide to build this package further.
func (w *Writer) clear() error {
for i := 0; i < w.lines; i++ {
if _, err := fmt.Fprintf(w.w, "\x1b[0A\x1b[2K\r"); err != nil {
return err
}
}
return nil
}