feat: add cache helpers

cache/blob.go

@@ -0,0 +1,56 @@
+package cache
+
+import (
+	"bytes"
+	"io"
+	"os"
+)
+
+type Blob interface {
+	io.ReaderAt
+	io.Closer
+	Size() int64
+}
+
+type byteBlob struct {
+	buf *bytes.Reader
+}
+
+func NewByteBlob(b []byte) Blob {
+	return &byteBlob{buf: bytes.NewReader(b)}
+}
+
+func (blob *byteBlob) ReadAt(p []byte, off int64) (n int, err error) {
+	return blob.buf.ReadAt(p, off)
+}
+
+func (blob *byteBlob) Size() int64 {
+	return blob.buf.Size()
+}
+
+func (blob *byteBlob) Close() error {
+	return nil
+}
+
+type fileBlob struct {
+	buf *os.File
+}
+
+func NewFileBlob(f *os.File) Blob {
+	return &fileBlob{buf: f}
+}
+
+func (blob *fileBlob) ReadAt(p []byte, off int64) (n int, err error) {
+	return blob.buf.ReadAt(p, off)
+}
+
+func (blob *fileBlob) Size() int64 {
+	if i, err := blob.buf.Stat(); err != nil {
+		return i.Size()
+	}
+	return 0
+}
+
+func (blob *fileBlob) Close() error {
+	return nil
+}