Update transfer configuration

Export transfer config fields.
Determine differ based on platform or config.
Get snapshotter from metadata store.

Signed-off-by: Derek McGowan <derek@mcg.dev>

plugins/transfer/plugin.go

@@ -21,13 +21,14 @@ import (
 
 	"github.com/containerd/containerd"
 	"github.com/containerd/containerd/diff"
+	"github.com/containerd/containerd/errdefs"
 	"github.com/containerd/containerd/leases"
+	"github.com/containerd/containerd/log"
 	"github.com/containerd/containerd/metadata"
 	"github.com/containerd/containerd/pkg/transfer/local"
 	"github.com/containerd/containerd/pkg/unpack"
 	"github.com/containerd/containerd/platforms"
 	"github.com/containerd/containerd/plugin"
-	"github.com/containerd/containerd/snapshots"
 
 	// Load packages with type registrations
 	_ "github.com/containerd/containerd/pkg/transfer/archive"
@@ -43,7 +44,6 @@ func init() {
 		Requires: []plugin.Type{
 			plugin.LeasePlugin,
 			plugin.MetadataPlugin,
-			plugin.SnapshotPlugin,
 			plugin.DiffPlugin,
 		},
 		Config: defaultConfig(),
@@ -59,35 +59,72 @@ func init() {
 				return nil, err
 			}
 
-			d, err := ic.Get(plugin.DiffPlugin)
-			if err != nil {
-				return nil, err
-			}
-
 			// Set configuration based on default or user input
 			var lc local.TransferConfig
-			lc.MaxConcurrentDownloads = config.maxConcurrentDownloads
-			lc.MaxConcurrentUploadedLayers = config.maxConcurrentUploadedLayers
-			for _, uc := range config.unpackConfiguration {
-				p, err := platforms.Parse(uc.platform)
+			lc.MaxConcurrentDownloads = config.MaxConcurrentDownloads
+			lc.MaxConcurrentUploadedLayers = config.MaxConcurrentUploadedLayers
+			for _, uc := range config.UnpackConfiguration {
+				p, err := platforms.Parse(uc.Platform)
 				if err != nil {
-					return nil, fmt.Errorf("%s: platform configuration %v invalid", plugin.TransferPlugin, uc.platform)
+					return nil, fmt.Errorf("%s: platform configuration %v invalid", plugin.TransferPlugin, uc.Platform)
 				}
 
-				s, err := ic.GetByID(plugin.SnapshotPlugin, uc.snapshotter)
+				sn := ms.Snapshotter(uc.Snapshotter)
+				if sn == nil {
+					return nil, fmt.Errorf("snapshotter %q not found: %w", uc.Snapshotter, errdefs.ErrNotFound)
+				}
+
+				diffPlugins, err := ic.GetByType(plugin.DiffPlugin)
 				if err != nil {
-					return nil, err
+					return nil, fmt.Errorf("error loading diff plugins: %w", err)
+				}
+				var applier diff.Applier
+				target := platforms.OnlyStrict(p)
+				if uc.Differ != "" {
+					plugin, ok := diffPlugins[uc.Differ]
+					if !ok {
+						return nil, fmt.Errorf("diff plugin %q: %w", uc.Differ, errdefs.ErrNotFound)
+					}
+					inst, err := plugin.Instance()
+					if err != nil {
+						return nil, fmt.Errorf("failed to get instance for diff plugin %q: %w", uc.Differ, err)
+					}
+					applier = inst.(diff.Applier)
+				} else {
+					for name, plugin := range diffPlugins {
+						var matched bool
+						for _, p := range plugin.Meta.Platforms {
+							if target.Match(p) {
+								matched = true
+							}
+						}
+						if !matched {
+							continue
+						}
+						if applier != nil {
+							log.G(ic.Context).Warnf("multiple differs match for platform, set `differ` option to choose, skipping %q", name)
+							continue
+						}
+						inst, err := plugin.Instance()
+						if err != nil {
+							return nil, fmt.Errorf("failed to get instance for diff plugin %q: %w", name, err)
+						}
+						applier = inst.(diff.Applier)
+					}
+				}
+				if applier == nil {
+					return nil, fmt.Errorf("no matching diff plugins: %w", errdefs.ErrNotFound)
 				}
 
 				up := unpack.Platform{
-					Platform:       platforms.OnlyStrict(p),
-					SnapshotterKey: uc.snapshotter,
-					Snapshotter:    s.(snapshots.Snapshotter),
-					Applier:        d.(diff.Applier),
+					Platform:       target,
+					SnapshotterKey: uc.Snapshotter,
+					Snapshotter:    sn,
+					Applier:        applier,
 				}
 				lc.UnpackPlatforms = append(lc.UnpackPlatforms, up)
 			}
-			lc.RegistryConfigPath = config.registryConfigPath
+			lc.RegistryConfigPath = config.RegistryConfigPath
 
 			return local.NewTransferService(l.(leases.Manager), ms.ContentStore(), metadata.NewImageStore(ms), &lc), nil
 		},
@@ -95,32 +132,38 @@ func init() {
 }
 
 type transferConfig struct {
-	// maxConcurrentDownloads is the max concurrent content downloads for pull.
-	maxConcurrentDownloads int `toml:"max_concurrent_downloads"`
+	// MaxConcurrentDownloads is the max concurrent content downloads for pull.
+	MaxConcurrentDownloads int `toml:"max_concurrent_downloads"`
 
-	// maxConcurrentUploadedLayers is the max concurrent uploads for push
-	maxConcurrentUploadedLayers int `toml:"max_concurrent_uploaded_layers"`
+	// MaxConcurrentUploadedLayers is the max concurrent uploads for push
+	MaxConcurrentUploadedLayers int `toml:"max_concurrent_uploaded_layers"`
 
-	// unpackConfiguration is used to read config from toml
-	unpackConfiguration []unpackConfiguration `toml:"unpack_config"`
+	// UnpackConfiguration is used to read config from toml
+	UnpackConfiguration []unpackConfiguration `toml:"unpack_config"`
 
-	// registryConfigPath is a path to the root directory containing registry-specific configurations
-	registryConfigPath string `toml:"config_path"`
+	// RegistryConfigPath is a path to the root directory containing registry-specific configurations
+	RegistryConfigPath string `toml:"config_path"`
 }
 
 type unpackConfiguration struct {
-	platform    string
-	snapshotter string
+	// Platform is the target unpack platform to match
+	Platform string `toml:"platform"`
+
+	// Snapshotter is the snapshotter to use to unpack
+	Snapshotter string `toml:"snapshotter"`
+
+	// Differ is the diff plugin to be used for apply
+	Differ string `toml:"differ"`
 }
 
 func defaultConfig() *transferConfig {
 	return &transferConfig{
-		maxConcurrentDownloads:      3,
-		maxConcurrentUploadedLayers: 3,
-		unpackConfiguration: []unpackConfiguration{
+		MaxConcurrentDownloads:      3,
+		MaxConcurrentUploadedLayers: 3,
+		UnpackConfiguration: []unpackConfiguration{
 			{
-				platform:    platforms.Format(platforms.DefaultSpec()),
-				snapshotter: containerd.DefaultSnapshotter,
+				Platform:    platforms.Format(platforms.DefaultSpec()),
+				Snapshotter: containerd.DefaultSnapshotter,
 			},
 		},
 	}