Add support for image platform (#2)

Author: giacomolanciano

extractor/docker/docker.go

@@ -54,6 +54,12 @@ func init() {
 func NewDockerExtractor(ctx context.Context, imageName string, option types.DockerOption) (Extractor, func(), error) {
 	ref := image.Reference{Name: imageName, IsFile: false}
 	transports := []string{"docker-daemon:", "docker://"}
+	if option.Platform != "" {
+		// When platform is specified, prioritize registry lookup so the manifest list
+		// can be filtered by OS/arch and fail fast if unsupported, instead of silently
+		// using a pre-existing local image from the daemon.
+		transports = []string{"docker://"}
+	}
 	return newDockerExtractor(ctx, ref, transports, option)
 }
 

extractor/image/image.go

@@ -3,6 +3,7 @@ package image
 import (
 	"context"
 	"io"
+	"strings"
 
 	"github.com/containers/image/v5/image"
 	"github.com/containers/image/v5/pkg/blobinfocache"
@@ -53,6 +54,11 @@ func NewImage(ctx context.Context, image Reference, transports []string, option
 	var domain string
 	var auth *imageTypes.DockerAuthConfig
 
+	osChoice, archChoice, variantChoice, err := parsePlatform(option.Platform)
+	if err != nil {
+		return RealImage{}, err
+	}
+
 	originalName := image.Name
 	if !image.IsFile {
 		named, err := reference.ParseNormalizedNamed(image.Name)
@@ -70,8 +76,9 @@ func NewImage(ctx context.Context, image Reference, transports []string, option
 	}
 
 	sys := &imageTypes.SystemContext{
-		// TODO: make OSChoice configurable
-		OSChoice:                          "linux",
+		OSChoice:                          osChoice,
+		ArchitectureChoice:                archChoice,
+		VariantChoice:                     variantChoice,
 		DockerAuthConfig:                  auth,
 		DockerDisableV1Ping:               option.SkipPing,
 		DockerInsecureSkipTLSVerify:       imageTypes.NewOptionalBool(option.InsecureSkipTLSVerify),
@@ -94,6 +101,31 @@ func NewImage(ctx context.Context, image Reference, transports []string, option
 	}, nil
 }
 
+func parsePlatform(p string) (osChoice, archChoice, variantChoice string, err error) {
+	osChoice = "linux"
+	if p == "" {
+		return osChoice, "", "", nil
+	}
+	parts := strings.Split(p, "/")
+	switch len(parts) {
+	case 1:
+		archChoice = parts[0]
+	case 2:
+		osChoice = parts[0]
+		archChoice = parts[1]
+	case 3:
+		osChoice = parts[0]
+		archChoice = parts[1]
+		variantChoice = parts[2]
+	default:
+		return "", "", "", xerrors.Errorf("invalid platform %q", p)
+	}
+	if osChoice == "" || archChoice == "" {
+		return "", "", "", xerrors.Errorf("invalid platform %q", p)
+	}
+	return osChoice, archChoice, variantChoice, nil
+}
+
 func newSource(ctx context.Context, imageName string, transports []string, sys *imageTypes.SystemContext) (
 	ImageSource, ImageCloser, error) {
 	err := xerrors.New("no valid transport")

types/docker.go

@@ -7,6 +7,9 @@ type DockerOption struct {
 	UserName string
 	Password string
 
+	// Platform (e.g. linux/amd64, linux/arm64/v8)
+	Platform string
+
 	// ECR
 	AwsAccessKey    string
 	AwsSecretKey    string