CRI: Move reference sorting to reference package

Signed-off-by: Maksym Pavlenko <pavlenko.maksym@gmail.com>

reference/sort.go

@@ -0,0 +1,75 @@
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package reference
+
+import (
+	"sort"
+
+	"github.com/containerd/containerd/reference/docker"
+)
+
+// Sort sorts references by refRank then string comparison
+func Sort(references []string) []string {
+	var prefs []docker.Reference
+	var bad []string
+
+	for _, ref := range references {
+		pref, err := docker.ParseAnyReference(ref)
+		if err != nil {
+			bad = append(bad, ref)
+		} else {
+			prefs = append(prefs, pref)
+		}
+	}
+	sort.Slice(prefs, func(a, b int) bool {
+		ar := refRank(prefs[a])
+		br := refRank(prefs[b])
+		if ar == br {
+			return prefs[a].String() < prefs[b].String()
+		}
+		return ar < br
+	})
+	sort.Strings(bad)
+	var refs []string
+	for _, pref := range prefs {
+		refs = append(refs, pref.String())
+	}
+	return append(refs, bad...)
+}
+
+// refRank ranks precedence for reference type, preferring higher information references
+// 1. Name + Tag + Digest
+// 2. Name + Tag
+// 3. Name + Digest
+// 4. Name
+// 5. Digest
+// 6. Parse error
+func refRank(ref docker.Reference) uint8 {
+	if _, ok := ref.(docker.Named); ok {
+		if _, ok = ref.(docker.Tagged); ok {
+			if _, ok = ref.(docker.Digested); ok {
+				return 1
+			}
+			return 2
+		}
+		if _, ok = ref.(docker.Digested); ok {
+			return 3
+		}
+		return 4
+	}
+	return 5
+}