cmd/dist: implement fetch prototype

With the rename of fetch to fetch-object, we now introduce the `fetch`
command. It will fetch all of the resources required for an image into
the content store. We'll still need to follow this up with metadata
registration but this is a good start.

Signed-off-by: Stephen J Day <stephen.day@docker.com>

progress/bar.go

@@ -0,0 +1,65 @@
+package progress
+
+import (
+	"bytes"
+	"fmt"
+)
+
+// TODO(stevvooe): We may want to support more interesting parameterization of
+// the bar. For now, it is very simple.
+
+// Bar provides a very simple progress bar implementation.
+//
+// Use with fmt.Printf and "r" to format the progress bar. A "-" flag makes it
+// progress from right to left.
+type Bar float64
+
+var _ fmt.Formatter = Bar(1.0)
+
+func (h Bar) Format(state fmt.State, r rune) {
+	switch r {
+	case 'r':
+	default:
+		panic(fmt.Sprintf("%v: unexpected format character", float64(h)))
+	}
+
+	if h > 1.0 {
+		h = 1.0
+	}
+
+	if h < 0.0 {
+		h = 0.0
+	}
+
+	if state.Flag('-') {
+		h = 1.0 - h
+	}
+
+	width, ok := state.Width()
+	if !ok {
+		// default width of 40
+		width = 40
+	}
+
+	var pad int
+
+	extra := len([]byte(green)) + len([]byte(reset))
+
+	p := make([]byte, width+extra)
+	p[0], p[len(p)-1] = '|', '|'
+	pad += 2
+
+	positive := int(Bar(width-pad) * h)
+	negative := width - pad - positive
+
+	n := 1
+	n += copy(p[n:], []byte(green))
+	n += copy(p[n:], bytes.Repeat([]byte("+"), positive))
+	n += copy(p[n:], []byte(reset))
+
+	if negative > 0 {
+		n += copy(p[n:len(p)-1], bytes.Repeat([]byte("-"), negative))
+	}
+
+	state.Write(p)
+}

progress/doc.go

@@ -0,0 +1,2 @@
+// Package progress assists in displaying human readable progress information.
+package progress

progress/escape.go

@@ -0,0 +1,8 @@
+package progress
+
+const (
+	escape = "\x1b"
+	reset  = escape + "[0m"
+	red    = escape + "[31m"
+	green  = escape + "[32m"
+)

progress/humaans.go

@@ -0,0 +1,25 @@
+package progress
+
+import (
+	"fmt"
+	"time"
+
+	units "github.com/docker/go-units"
+)
+
+// Bytes converts a regular int64 to human readable type.
+type Bytes int64
+
+func (b Bytes) String() string {
+	return units.CustomSize("%02.1f %s", float64(b), 1024.0, []string{"B", "KiB", "MiB", "GiB", "TiB", "PiB", "EiB", "ZiB", "YiB"})
+}
+
+type BytesPerSecond int64
+
+func NewBytesPerSecond(n int64, duration time.Duration) BytesPerSecond {
+	return BytesPerSecond(float64(n) / duration.Seconds())
+}
+
+func (bps BytesPerSecond) String() string {
+	return fmt.Sprintf("%v/s", Bytes(bps))
+}

progress/writer.go

@@ -0,0 +1,60 @@
+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
+}