systemcontext: make selection of ZstdImages configurable

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

manifest/oci_index.go

@@ -76,7 +76,7 @@ func (index *OCI1Index) UpdateInstances(updates []ListUpdate) error {
 	return nil
 }
 
-func instanceBetterMatchesPlatforms(manifests []imgspecv1.Descriptor, platformCheck bool, wantedPlatform imgspecv1.Platform) digest.Digest {
+func instanceBetterMatchesPlatforms(ctx *types.SystemContext, manifests []imgspecv1.Descriptor, platformCheck bool, wantedPlatform imgspecv1.Platform) digest.Digest {
 	var matchedDigest digest.Digest
 	matchedDigest = ""
 	for _, d := range manifests {
@@ -97,13 +97,13 @@ func instanceBetterMatchesPlatforms(manifests []imgspecv1.Descriptor, platformCh
 			if matchedDigest == "" {
 				matchedDigest = d.Digest
 			}
-			// Always give priority to zstd if more than one image
-			// exists for the same platform.
-			// TODO: In future this check will be configurable and
-			// will be relayed via `ctx`.
-			if _, ok := d.Annotations[OCI1InstanceAnnotationCompressionZSTD]; ok {
-				matchedDigest = d.Digest
-				return matchedDigest
+			if ctx.GivePriorityToZstdImages != types.OptionalBoolFalse {
+				// Always give priority to zstd if more than one image
+				// exists for the same platform.
+				if _, ok := d.Annotations[OCI1InstanceAnnotationCompressionZSTD]; ok {
+					matchedDigest = d.Digest
+					return matchedDigest
+				}
 			}
 		}
 	}
@@ -119,13 +119,13 @@ func (index *OCI1Index) ChooseInstance(ctx *types.SystemContext) (digest.Digest,
 	}
 	var matchedDigest digest.Digest
 	for _, wantedPlatform := range wantedPlatforms {
-		matchedDigest = instanceBetterMatchesPlatforms(index.Manifests, true, wantedPlatform)
+		matchedDigest = instanceBetterMatchesPlatforms(ctx, index.Manifests, true, wantedPlatform)
 		if matchedDigest != "" {
 			return matchedDigest, nil
 		}
 	}
 
-	matchedDigest = instanceBetterMatchesPlatforms(index.Manifests, false, imgspecv1.Platform{})
+	matchedDigest = instanceBetterMatchesPlatforms(ctx, index.Manifests, false, imgspecv1.Platform{})
 	if matchedDigest != "" {
 		return matchedDigest, nil
 	}

types/types.go

@@ -671,6 +671,9 @@ type SystemContext struct {
 	CompressionFormat *compression.Algorithm
 	// CompressionLevel specifies what compression level is used
 	CompressionLevel *int
+	// Give priority to pulling zstd images if multiple images are present unless explicitly
+	// configured false.
+	GivePriorityToZstdImages OptionalBool
 }
 
 // ProgressEvent is the type of events a progress reader can produce