Update client Image to have configurable platform

Separate Fetch and Pull commands in client to distinguish
between platform specific and non-platform specific operations.
`ctr images pull` with all platforms will now unpack all platforms.
`ctr content fetch` now supports platform flags.

Signed-off-by: Derek McGowan <derek@mcgstyle.net>

client.go

@@ -45,6 +45,7 @@ import (
 	"github.com/containerd/containerd/images"
 	"github.com/containerd/containerd/namespaces"
 	"github.com/containerd/containerd/pkg/dialer"
+	"github.com/containerd/containerd/platforms"
 	"github.com/containerd/containerd/plugin"
 	"github.com/containerd/containerd/remotes"
 	"github.com/containerd/containerd/remotes/docker"
@@ -284,7 +285,31 @@ func defaultRemoteContext() *RemoteContext {
 	}
 }
 
+// Fetch downloads the provided content into containerd's content store
+// and returns a non-platform specific image reference
+func (c *Client) Fetch(ctx context.Context, ref string, opts ...RemoteOpt) (images.Image, error) {
+	fetchCtx := defaultRemoteContext()
+	for _, o := range opts {
+		if err := o(c, fetchCtx); err != nil {
+			return images.Image{}, err
+		}
+	}
+
+	if fetchCtx.Unpack {
+		return images.Image{}, errors.New("unpack on fetch not supported, try pull")
+	}
+
+	ctx, done, err := c.WithLease(ctx)
+	if err != nil {
+		return images.Image{}, err
+	}
+	defer done(ctx)
+
+	return c.fetch(ctx, fetchCtx, ref)
+}
+
 // Pull downloads the provided content into containerd's content store
+// and returns a platform specific image object
 func (c *Client) Pull(ctx context.Context, ref string, opts ...RemoteOpt) (Image, error) {
 	pullCtx := defaultRemoteContext()
 	for _, o := range opts {
@@ -292,7 +317,12 @@ func (c *Client) Pull(ctx context.Context, ref string, opts ...RemoteOpt) (Image
 			return nil, err
 		}
 	}
-	store := c.ContentStore()
+
+	if len(pullCtx.Platforms) > 1 {
+		return nil, errors.New("cannot pull multiplatform image locally, try Fetch")
+	} else if len(pullCtx.Platforms) == 0 {
+		pullCtx.Platforms = []string{platforms.Default()}
+	}
 
 	ctx, done, err := c.WithLease(ctx)
 	if err != nil {
@@ -300,82 +330,92 @@ func (c *Client) Pull(ctx context.Context, ref string, opts ...RemoteOpt) (Image
 	}
 	defer done(ctx)
 
-	name, desc, err := pullCtx.Resolver.Resolve(ctx, ref)
+	img, err := c.fetch(ctx, pullCtx, ref)
 	if err != nil {
-		return nil, errors.Wrapf(err, "failed to resolve reference %q", ref)
+		return nil, err
 	}
 
-	fetcher, err := pullCtx.Resolver.Fetcher(ctx, name)
+	i := NewImageWithPlatform(c, img, pullCtx.Platforms[0])
+
+	if pullCtx.Unpack {
+		if err := i.Unpack(ctx, pullCtx.Snapshotter); err != nil {
+			return nil, errors.Wrapf(err, "failed to unpack image on snapshotter %s", pullCtx.Snapshotter)
+		}
+	}
+
+	return i, nil
+}
+
+func (c *Client) fetch(ctx context.Context, rCtx *RemoteContext, ref string) (images.Image, error) {
+	store := c.ContentStore()
+	name, desc, err := rCtx.Resolver.Resolve(ctx, ref)
 	if err != nil {
-		return nil, errors.Wrapf(err, "failed to get fetcher for %q", name)
+		return images.Image{}, errors.Wrapf(err, "failed to resolve reference %q", ref)
+	}
+
+	fetcher, err := rCtx.Resolver.Fetcher(ctx, name)
+	if err != nil {
+		return images.Image{}, errors.Wrapf(err, "failed to get fetcher for %q", name)
 	}
 
 	var (
 		schema1Converter *schema1.Converter
 		handler          images.Handler
 	)
-	if desc.MediaType == images.MediaTypeDockerSchema1Manifest && pullCtx.ConvertSchema1 {
+	if desc.MediaType == images.MediaTypeDockerSchema1Manifest && rCtx.ConvertSchema1 {
 		schema1Converter = schema1.NewConverter(store, fetcher)
-		handler = images.Handlers(append(pullCtx.BaseHandlers, schema1Converter)...)
+		handler = images.Handlers(append(rCtx.BaseHandlers, schema1Converter)...)
 	} else {
 		// Get all the children for a descriptor
 		childrenHandler := images.ChildrenHandler(store)
 		// Set any children labels for that content
 		childrenHandler = images.SetChildrenLabels(store, childrenHandler)
 		// Filter children by platforms
-		childrenHandler = images.FilterPlatforms(childrenHandler, pullCtx.Platforms...)
+		childrenHandler = images.FilterPlatforms(childrenHandler, rCtx.Platforms...)
 
-		handler = images.Handlers(append(pullCtx.BaseHandlers,
+		handler = images.Handlers(append(rCtx.BaseHandlers,
 			remotes.FetchHandler(store, fetcher),
 			childrenHandler,
 		)...)
 	}
 
 	if err := images.Dispatch(ctx, handler, desc); err != nil {
-		return nil, err
+		return images.Image{}, err
 	}
 	if schema1Converter != nil {
 		desc, err = schema1Converter.Convert(ctx)
 		if err != nil {
-			return nil, err
+			return images.Image{}, err
 		}
 	}
 
-	img := &image{
-		client: c,
-		i: images.Image{
-			Name:   name,
-			Target: desc,
-			Labels: pullCtx.Labels,
-		},
-	}
-
-	if pullCtx.Unpack {
-		if err := img.Unpack(ctx, pullCtx.Snapshotter); err != nil {
-			return nil, errors.Wrapf(err, "failed to unpack image on snapshotter %s", pullCtx.Snapshotter)
-		}
+	img := images.Image{
+		Name:   name,
+		Target: desc,
+		Labels: rCtx.Labels,
 	}
 
 	is := c.ImageService()
 	for {
-		if created, err := is.Create(ctx, img.i); err != nil {
+		if created, err := is.Create(ctx, img); err != nil {
 			if !errdefs.IsAlreadyExists(err) {
-				return nil, err
+				return images.Image{}, err
 			}
 
-			updated, err := is.Update(ctx, img.i)
+			updated, err := is.Update(ctx, img)
 			if err != nil {
 				// if image was removed, try create again
 				if errdefs.IsNotFound(err) {
 					continue
 				}
-				return nil, err
+				return images.Image{}, err
 			}
 
-			img.i = updated
+			img = updated
 		} else {
-			img.i = created
+			img = created
 		}
+
 		return img, nil
 	}
 }