Fix snapshotter getter in client code

Fixes #3312

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

client.go

@@ -43,6 +43,7 @@ import (
 	"github.com/containerd/containerd/content"
 	contentproxy "github.com/containerd/containerd/content/proxy"
 	"github.com/containerd/containerd/defaults"
+	"github.com/containerd/containerd/errdefs"
 	"github.com/containerd/containerd/events"
 	"github.com/containerd/containerd/images"
 	"github.com/containerd/containerd/leases"
@@ -655,6 +656,14 @@ func (c *Client) Version(ctx context.Context) (Version, error) {
 	}, nil
 }
 
+func (c *Client) getSnapshotter(name string) (snapshots.Snapshotter, error) {
+	s := c.SnapshotService(name)
+	if s == nil {
+		return nil, errors.Wrapf(errdefs.ErrNotFound, "snapshotter %s was not found", name)
+	}
+	return s, nil
+}
+
 // CheckRuntime returns true if the current runtime matches the expected
 // runtime. Providing various parts of the runtime schema will match those
 // parts of the expected runtime

container.go

@@ -233,7 +233,11 @@ func (c *container) NewTask(ctx context.Context, ioCreate cio.Creator, opts ...N
 		}
 
 		// get the rootfs from the snapshotter and add it to the request
-		mounts, err := c.client.SnapshotService(r.Snapshotter).Mounts(ctx, r.SnapshotKey)
+		s, err := c.client.getSnapshotter(r.Snapshotter)
+		if err != nil {
+			return nil, err
+		}
+		mounts, err := s.Mounts(ctx, r.SnapshotKey)
 		if err != nil {
 			return nil, err
 		}

container_opts.go

@@ -120,7 +120,11 @@ func WithSnapshot(id string) NewContainerOpts {
 	return func(ctx context.Context, client *Client, c *containers.Container) error {
 		setSnapshotterIfEmpty(ctx, client, c)
 		// check that the snapshot exists, if not, fail on creation
-		if _, err := client.SnapshotService(c.Snapshotter).Mounts(ctx, id); err != nil {
+		s, err := client.getSnapshotter(c.Snapshotter)
+		if err != nil {
+			return err
+		}
+		if _, err := s.Mounts(ctx, id); err != nil {
 			return err
 		}
 		c.SnapshotKey = id
@@ -138,7 +142,11 @@ func WithNewSnapshot(id string, i Image, opts ...snapshots.Opt) NewContainerOpts
 		}
 		setSnapshotterIfEmpty(ctx, client, c)
 		parent := identity.ChainID(diffIDs).String()
-		if _, err := client.SnapshotService(c.Snapshotter).Prepare(ctx, id, parent, opts...); err != nil {
+		s, err := client.getSnapshotter(c.Snapshotter)
+		if err != nil {
+			return err
+		}
+		if _, err := s.Prepare(ctx, id, parent, opts...); err != nil {
 			return err
 		}
 		c.SnapshotKey = id
@@ -153,7 +161,11 @@ func WithSnapshotCleanup(ctx context.Context, client *Client, c containers.Conta
 		if c.Snapshotter == "" {
 			return errors.Wrapf(errdefs.ErrInvalidArgument, "container.Snapshotter must be set to cleanup rootfs snapshot")
 		}
-		return client.SnapshotService(c.Snapshotter).Remove(ctx, c.SnapshotKey)
+		s, err := client.getSnapshotter(c.Snapshotter)
+		if err != nil {
+			return err
+		}
+		return s.Remove(ctx, c.SnapshotKey)
 	}
 	return nil
 }
@@ -168,7 +180,11 @@ func WithNewSnapshotView(id string, i Image, opts ...snapshots.Opt) NewContainer
 		}
 		setSnapshotterIfEmpty(ctx, client, c)
 		parent := identity.ChainID(diffIDs).String()
-		if _, err := client.SnapshotService(c.Snapshotter).View(ctx, id, parent, opts...); err != nil {
+		s, err := client.getSnapshotter(c.Snapshotter)
+		if err != nil {
+			return err
+		}
+		if _, err := s.View(ctx, id, parent, opts...); err != nil {
 			return err
 		}
 		c.SnapshotKey = id

container_opts_unix.go

@@ -53,10 +53,13 @@ func withRemappedSnapshotBase(id string, i Image, uid, gid uint32, readonly bool
 		setSnapshotterIfEmpty(ctx, client, c)
 
 		var (
-			snapshotter = client.SnapshotService(c.Snapshotter)
+			parent   = identity.ChainID(diffIDs).String()
-			parent      = identity.ChainID(diffIDs).String()
+			usernsID = fmt.Sprintf("%s-%d-%d", parent, uid, gid)
-			usernsID    = fmt.Sprintf("%s-%d-%d", parent, uid, gid)
 		)
+		snapshotter, err := client.getSnapshotter(c.Snapshotter)
+		if err != nil {
+			return err
+		}
 		if _, err := snapshotter.Stat(ctx, usernsID); err == nil {
 			if _, err := snapshotter.Prepare(ctx, id, usernsID); err == nil {
 				c.SnapshotKey = id

image.go

@@ -108,7 +108,10 @@ func (i *image) Config(ctx context.Context) (ocispec.Descriptor, error) {
 }
 
 func (i *image) IsUnpacked(ctx context.Context, snapshotterName string) (bool, error) {
-	sn := i.client.SnapshotService(snapshotterName)
+	sn, err := i.client.getSnapshotter(snapshotterName)
+	if err != nil {
+		return false, err
+	}
 	cs := i.client.ContentStore()
 
 	diffs, err := i.i.RootFS(ctx, cs, i.platform)
@@ -140,13 +143,16 @@ func (i *image) Unpack(ctx context.Context, snapshotterName string) error {
 	}
 
 	var (
-		sn = i.client.SnapshotService(snapshotterName)
 		a  = i.client.DiffService()
 		cs = i.client.ContentStore()
 
 		chain    []digest.Digest
 		unpacked bool
 	)
+	sn, err := i.client.getSnapshotter(snapshotterName)
+	if err != nil {
+		return err
+	}
 	for _, layer := range layers {
 		unpacked, err = rootfs.ApplyLayer(ctx, layer, chain, sn, a)
 		if err != nil {