ctr: add commands package with shared utility functions

Signed-off-by: Jess Valarezo <valarezo.jessica@gmail.com>

cmd/ctr/commands/commands.go

@@ -0,0 +1,84 @@
+package commands
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+	"strings"
+
+	"github.com/containerd/containerd"
+	"github.com/urfave/cli"
+)
+
+var (
+	// SnapshotterFlags are cli flags specifying snapshotter names
+	SnapshotterFlags = []cli.Flag{
+		cli.StringFlag{
+			Name:  "snapshotter",
+			Usage: "snapshotter name. Empty value stands for the daemon default value.",
+			Value: containerd.DefaultSnapshotter,
+		},
+	}
+
+	// LabelFlag is a cli flag specifying labels
+	LabelFlag = cli.StringSliceFlag{
+		Name:  "label",
+		Usage: "labels to attach to the image",
+	}
+
+	// RegistryFlags are cli flags specifying registry options
+	RegistryFlags = []cli.Flag{
+		cli.BoolFlag{
+			Name:  "skip-verify,k",
+			Usage: "skip SSL certificate validation",
+		},
+		cli.BoolFlag{
+			Name:  "plain-http",
+			Usage: "allow connections using plain HTTP",
+		},
+		cli.StringFlag{
+			Name:  "user,u",
+			Usage: "user[:password] Registry user and password",
+		},
+		cli.StringFlag{
+			Name:  "refresh",
+			Usage: "refresh token for authorization server",
+		},
+	}
+)
+
+// ObjectWithLabelArgs returns the first arg and a LabelArgs object
+func ObjectWithLabelArgs(clicontext *cli.Context) (string, map[string]string) {
+	var (
+		first        = clicontext.Args().First()
+		labelStrings = clicontext.Args().Tail()
+	)
+
+	return first, LabelArgs(labelStrings)
+}
+
+// LabelArgs returns a map of label key,value pairs
+func LabelArgs(labelStrings []string) map[string]string {
+	labels := make(map[string]string, len(labelStrings))
+	for _, label := range labelStrings {
+		parts := strings.SplitN(label, "=", 2)
+		key := parts[0]
+		value := "true"
+		if len(parts) > 1 {
+			value = parts[1]
+		}
+
+		labels[key] = value
+	}
+
+	return labels
+}
+
+// PrintAsJSON prints input in JSON format
+func PrintAsJSON(x interface{}) {
+	b, err := json.MarshalIndent(x, "", "    ")
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "can't marshal %+v as a JSON string: %v\n", x, err)
+	}
+	fmt.Println(string(b))
+}