libimage.NormalizePlatform: normalize default variant as per specified arch

As of now NormalizePlatform ignores normalizing or setting default
variants for specific arch types thus producing empty variants in
results even when default variants were expected for such cases.

Example consider: `linux/armhf` -> `{os:linux, arch: arm, variant: v7}`

Signed-off-by: Aditya R <arajan@redhat.com>

common/libimage/normalize_test.go

@@ -54,6 +54,34 @@ func TestNormalizePlatform(t *testing.T) {
 			platform{"linux", "aarch64", ""},
 			platform{"linux", "arm64", ""},
 		},
+		// Verify: https://github.com/containerd/containerd/blob/main/platforms/database.go#L97
+		{
+			platform{"linux", "arm64", "8"},
+			platform{"linux", "arm64", "v8"},
+		},
+		// Verify: https://github.com/containerd/containerd/blob/main/platforms/database.go#L100
+		{
+			platform{"linux", "armhf", ""},
+			platform{"linux", "arm", "v7"},
+		},
+		{
+			platform{"linux", "armhf", "v7"},
+			platform{"linux", "arm", "v7"},
+		},
+		// Verify: https://github.com/containerd/containerd/blob/main/platforms/database.go#L103
+		{
+			platform{"linux", "armel", ""},
+			platform{"linux", "arm", "v6"},
+		},
+		// Verify: https://github.com/containerd/containerd/blob/main/platforms/database.go#L103
+		{
+			platform{"linux", "armel", "v6"},
+			platform{"linux", "arm", "v6"},
+		},
+		{
+			platform{"linux", "armel", ""},
+			platform{"linux", "arm", "v6"},
+		},
 	} {
 		os, arch, variant := NormalizePlatform(test.input.os, test.input.arch, test.input.variant)
 		assert.Equal(t, test.expected.os, os, test.input)

common/libimage/platform.go

@@ -6,6 +6,7 @@ import (
 	"runtime"
 
 	"github.com/containerd/containerd/platforms"
+	v1 "github.com/opencontainers/image-spec/specs-go/v1"
 	"github.com/sirupsen/logrus"
 )
 
@@ -20,9 +21,18 @@ const (
 )
 
 // NormalizePlatform normalizes (according to the OCI spec) the specified os,
-// arch and variant.  If left empty, the individual item will not be normalized.
+// arch and variant.  If left empty, the individual item will be normalized.
 func NormalizePlatform(rawOS, rawArch, rawVariant string) (os, arch, variant string) {
-	rawPlatform := toPlatformString(rawOS, rawArch, rawVariant)
+	platformSpec := v1.Platform{
+		OS:           rawOS,
+		Architecture: rawArch,
+		Variant:      rawVariant,
+	}
+	normalizedSpec := platforms.Normalize(platformSpec)
+	if normalizedSpec.Variant == "" && rawVariant != "" {
+		normalizedSpec.Variant = rawVariant
+	}
+	rawPlatform := toPlatformString(normalizedSpec.OS, normalizedSpec.Architecture, normalizedSpec.Variant)
 	normalizedPlatform, err := platforms.Parse(rawPlatform)
 	if err != nil {
 		logrus.Debugf("Error normalizing platform: %v", err)
@@ -38,7 +48,7 @@ func NormalizePlatform(rawOS, rawArch, rawVariant string) (os, arch, variant str
 		arch = normalizedPlatform.Architecture
 	}
 	variant = rawVariant
-	if rawVariant != "" {
+	if rawVariant != "" || (rawVariant == "" && normalizedPlatform.Variant != "") {
 		variant = normalizedPlatform.Variant
 	}
 	return os, arch, variant