Move content/local to plugins/content/local

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

plugins/content/local/readerat.go

@@ -0,0 +1,72 @@
+/*
+   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 local
+
+import (
+	"fmt"
+	"io"
+	"os"
+
+	"github.com/containerd/containerd/v2/content"
+	"github.com/containerd/containerd/v2/errdefs"
+)
+
+// readerat implements io.ReaderAt in a completely stateless manner by opening
+// the referenced file for each call to ReadAt.
+type sizeReaderAt struct {
+	size int64
+	fp   *os.File
+}
+
+// OpenReader creates ReaderAt from a file
+func OpenReader(p string) (content.ReaderAt, error) {
+	fi, err := os.Stat(p)
+	if err != nil {
+		if !os.IsNotExist(err) {
+			return nil, err
+		}
+
+		return nil, fmt.Errorf("blob not found: %w", errdefs.ErrNotFound)
+	}
+
+	fp, err := os.Open(p)
+	if err != nil {
+		if !os.IsNotExist(err) {
+			return nil, err
+		}
+
+		return nil, fmt.Errorf("blob not found: %w", errdefs.ErrNotFound)
+	}
+
+	return sizeReaderAt{size: fi.Size(), fp: fp}, nil
+}
+
+func (ra sizeReaderAt) ReadAt(p []byte, offset int64) (int, error) {
+	return ra.fp.ReadAt(p, offset)
+}
+
+func (ra sizeReaderAt) Size() int64 {
+	return ra.size
+}
+
+func (ra sizeReaderAt) Close() error {
+	return ra.fp.Close()
+}
+
+func (ra sizeReaderAt) Reader() io.Reader {
+	return io.LimitReader(ra.fp, ra.size)
+}