added fs encryption overlay

pkg/provider/crypto/reader.go

@@ -0,0 +1,107 @@
+package crypto
+
+import (
+	"crypto/cipher"
+	"errors"
+	"io"
+
+	"golang.org/x/crypto/chacha20poly1305"
+)
+
+type cryptoReader interface {
+	io.Reader
+	io.ReaderAt
+}
+
+type reader struct {
+	a   cipher.AEAD
+	src cryptoReader
+
+	unread []byte // decrypted but unread data, backed by buf
+	buf    [FullSize]byte
+	off    int64
+
+	err   error
+	nonce [NonceSize]byte
+}
+
+func newReader(key []byte, src cryptoReader) (*reader, error) {
+	aead, err := chacha20poly1305.New(key)
+	if err != nil {
+		return nil, err
+	}
+	return &reader{
+		a:   aead,
+		src: src,
+	}, nil
+}
+
+func (r *reader) Read(p []byte) (int, error) {
+	if len(r.unread) > 0 {
+		n := copy(p, r.unread)
+		r.unread = r.unread[n:]
+		return n, nil
+	}
+	if r.err != nil {
+		return 0, r.err
+	}
+	if len(p) == 0 {
+		return 0, nil
+	}
+
+	last, err := r.readChunk()
+	if err != nil {
+		r.err = err
+		return 0, err
+	}
+	if r.off > 0 && len(r.unread) >= int(r.off) {
+		r.unread = r.unread[r.off:]
+		r.off = 0
+	}
+
+	n := copy(p, r.unread)
+	r.unread = r.unread[n:]
+
+	if last {
+		r.err = io.EOF
+	}
+
+	return n, nil
+}
+
+func (r *reader) readChunk() (last bool, err error) {
+	if len(r.unread) != 0 {
+		panic("stream: internal error: readChunk called with dirty buffer")
+	}
+
+	in := r.buf[:]
+	n, err := io.ReadFull(r.src, in)
+	switch {
+	case err == io.EOF:
+		// A message can't end without a marked chunk. This message is truncated.
+		return false, io.ErrUnexpectedEOF
+	case err == io.ErrUnexpectedEOF:
+		// The last chunk can be short.
+		in = in[:n]
+		last = true
+		setLastChunkFlag(&r.nonce)
+	case err != nil:
+		return false, err
+	}
+
+	outBuf := make([]byte, 0, ChunkSize)
+	out, err := r.a.Open(outBuf, r.nonce[:], in, nil)
+	if err != nil && !last {
+		// Check if this was a full-length final chunk.
+		last = true
+		setLastChunkFlag(&r.nonce)
+		out, err = r.a.Open(outBuf, r.nonce[:], in, nil)
+	}
+	if err != nil {
+		return false, errors.New("failed to decrypt and authenticate payload chunk")
+	}
+
+	incNonce(&r.nonce)
+	r.unread = r.buf[:copy(r.buf[:], out)]
+	return last, nil
+}