api/services/content: define delete method

Allow deletion of content over the GRPC interface. For now, we are going
with a model that conducts reference management outside of the content
store, in the metadata store but this design is valid either way.

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

cmd/dist/delete.go

@@ -1,9 +1,12 @@
 package main
 
 import (
-	contextpkg "context"
 	"fmt"
 
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/codes"
+
+	contentapi "github.com/docker/containerd/api/services/content"
 	"github.com/docker/containerd/log"
 	digest "github.com/opencontainers/go-digest"
 	"github.com/urfave/cli"
@@ -11,7 +14,7 @@ import (
 
 var deleteCommand = cli.Command{
 	Name:      "delete",
-	Aliases:   []string{"del"},
+	Aliases:   []string{"delete", "del", "remove", "rm"},
 	Usage:     "permanently delete one or more blobs.",
 	ArgsUsage: "[flags] [<digest>, ...]",
 	Description: `Delete one or more blobs permanently. Successfully deleted
@@ -19,16 +22,18 @@ var deleteCommand = cli.Command{
 	Flags: []cli.Flag{},
 	Action: func(context *cli.Context) error {
 		var (
-			ctx       = contextpkg.Background()
+			ctx       = background
 			args      = []string(context.Args())
 			exitError error
 		)
 
-		cs, err := resolveContentStore(context)
+		conn, err := connectGRPC(context)
 		if err != nil {
 			return err
 		}
 
+		client := contentapi.NewContentClient(conn)
+
 		for _, arg := range args {
 			dgst, err := digest.Parse(arg)
 			if err != nil {
@@ -39,11 +44,18 @@ var deleteCommand = cli.Command{
 				continue
 			}
 
-			if err := cs.Delete(dgst); err != nil {
-				if exitError == nil {
-					exitError = err
+			if _, err := client.Delete(ctx, &contentapi.DeleteContentRequest{
+				Digest: dgst,
+			}); err != nil {
+				switch grpc.Code(err) {
+				case codes.NotFound:
+					// if it is already deleted, ignore!
+				default:
+					if exitError == nil {
+						exitError = err
+					}
+					log.G(ctx).WithError(err).Errorf("could not delete %v", dgst)
 				}
-				log.G(ctx).WithError(err).Errorf("could not delete %v", dgst)
 				continue
 			}