adds go flags type for byte size

flagext/byte_size.go

@@ -0,0 +1,23 @@
+package flagext
+
+import (
+	"github.com/docker/go-units"
+)
+
+// ByteSize used to pass byte sizes to a go-flags CLI
+type ByteSize int
+
+// MarshalFlag implements go-flags Marshaller interface
+func (b ByteSize) MarshalFlag() (string, error) {
+	return units.HumanSize(float64(b)), nil
+}
+
+// UnmarshalFlag implements go-flags Unmarshaller interface
+func (b *ByteSize) UnmarshalFlag(value string) error {
+	sz, err := units.FromHumanSize(value)
+	if err != nil {
+		return err
+	}
+	*b = ByteSize(int(sz))
+	return nil
+}

flagext/byte_size_test.go

@@ -0,0 +1,22 @@
+package flagext
+
+import "testing"
+import "github.com/stretchr/testify/assert"
+
+func TestMarshalBytesize(t *testing.T) {
+	v, err := ByteSize(1024).MarshalFlag()
+	if assert.NoError(t, err) {
+		assert.Equal(t, "1.024 kB", v)
+	}
+}
+
+func TestUnmarshalBytesize(t *testing.T) {
+	var b ByteSize
+	err := b.UnmarshalFlag("notASize")
+	assert.Error(t, err)
+
+	err = b.UnmarshalFlag("1MB")
+	if assert.NoError(t, err) {
+		assert.Equal(t, ByteSize(1000000), b)
+	}
+}