Move labels to pkg/labels

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

pkg/labels/validate.go

@@ -0,0 +1,41 @@
+/*
+   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 labels
+
+import (
+	"fmt"
+
+	"github.com/containerd/containerd/v2/pkg/errdefs"
+)
+
+const (
+	maxSize = 4096
+	// maximum length of key portion of error message if len of key + len of value > maxSize
+	keyMaxLen = 64
+)
+
+// Validate a label's key and value are under 4096 bytes
+func Validate(k, v string) error {
+	total := len(k) + len(v)
+	if total > maxSize {
+		if len(k) > keyMaxLen {
+			k = k[:keyMaxLen]
+		}
+		return fmt.Errorf("label key and value length (%d bytes) greater than maximum size (%d bytes), key: %s: %w", total, maxSize, k, errdefs.ErrInvalidArgument)
+	}
+	return nil
+}