From 58f0d2be5a4356307dfecba56f1fd0ea982f6a92 Mon Sep 17 00:00:00 2001
From: Gilbert Chen <gchen@acrosync.com>
Date: Tue, 22 Nov 2022 21:31:24 -0500
Subject: [PATCH] Fixed a bug that didn't preserve the version bit when copying
 old snapshots

The version bit should not be set to 1 when encoding a snapshot.  Instead,
it must be set to 1 on snapshot creation.

To correctly process old snapshots encoded incorrectly with version bit set
to 1, the first byte of the encoded file list is also checked.  If the first
byte is `[`, then it must be an old snapshot, since the file list in the new
snapshot format always starts with a string encoded in msgpack, the first
byte of which can't be `[`.
---
 src/duplicacy_snapshot.go        | 31 +++++++++++++++----------------
 src/duplicacy_snapshotmanager.go | 26 +++++++++++++++++++++++---
 2 files changed, 38 insertions(+), 19 deletions(-)

diff --git a/src/duplicacy_snapshot.go b/src/duplicacy_snapshot.go
index 4fe8df7..e7511b6 100644
--- a/src/duplicacy_snapshot.go
+++ b/src/duplicacy_snapshot.go
@@ -15,7 +15,6 @@ import (
 	"strings"
 	"time"
 	"sort"
-	"bytes"
 
     "github.com/vmihailenco/msgpack"
 
@@ -52,6 +51,7 @@ type Snapshot struct {
 // CreateEmptySnapshot creates an empty snapshot.
 func CreateEmptySnapshot(id string) (snapshto *Snapshot) {
 	return &Snapshot{
+		Version:   1,
 		ID:        id,
 		Revision:  0,
 		StartTime: time.Now().Unix(),
@@ -112,22 +112,21 @@ func (snapshot *Snapshot)ListRemoteFiles(config *Config, chunkOperator *ChunkOpe
 	}
 
 	var chunk *Chunk
-	reader := sequenceReader{
-		sequence: snapshot.FileSequence,
-		buffer:   new(bytes.Buffer),
-		refillFunc: func(chunkHash string) []byte {
-			if chunk != nil {
-				config.PutChunk(chunk)
-			}
-			chunk = chunkOperator.Download(chunkHash, 0, true)
-			return chunk.GetBytes()
-		},
-	}
+	reader := NewSequenceReader(snapshot.FileSequence, func(chunkHash string) []byte {
+		if chunk != nil {
+			config.PutChunk(chunk)
+		}
+		chunk = chunkOperator.Download(chunkHash, 0, true)
+		return chunk.GetBytes()
+	})
 
-	if snapshot.Version == 0 {
+	// Normally if Version is 0 then the snapshot is created by CLI v2 but unfortunately CLI 3.0.1 does not set the
+	// version bit correctly when copying old backups.  So we need to check the first byte -- if it is '[' then it is
+	// the old format.  The new format starts with a string encoded in msgpack and the first byte can't be '['.
+	if snapshot.Version == 0 || reader.GetFirstByte() == '['{
 		LOG_INFO("SNAPSHOT_VERSION", "snapshot %s at revision %d is encoded in an old version format", snapshot.ID, snapshot.Revision)
 		files := make([]*Entry, 0)
-		decoder := json.NewDecoder(&reader)
+		decoder := json.NewDecoder(reader)
 
 		// read open bracket
 		_, err := decoder.Token()
@@ -156,7 +155,7 @@ func (snapshot *Snapshot)ListRemoteFiles(config *Config, chunkOperator *ChunkOpe
 			}
 		}
 	} else if snapshot.Version == 1 {
-		decoder := msgpack.NewDecoder(&reader)
+		decoder := msgpack.NewDecoder(reader)
 
 		lastEndChunk := 0
 
@@ -434,7 +433,7 @@ func (snapshot *Snapshot) MarshalJSON() ([]byte, error) {
 
 	object := make(map[string]interface{})
 
-	object["version"] = 1
+	object["version"] = snapshot.Version
 	object["id"] = snapshot.ID
 	object["revision"] = snapshot.Revision
 	object["options"] = snapshot.Options
diff --git a/src/duplicacy_snapshotmanager.go b/src/duplicacy_snapshotmanager.go
index c44c194..1a94f09 100644
--- a/src/duplicacy_snapshotmanager.go
+++ b/src/duplicacy_snapshotmanager.go
@@ -249,17 +249,27 @@ func (manager *SnapshotManager) DownloadSnapshot(snapshotID string, revision int
 // the memory before passing them to the json unmarshaller.
 type sequenceReader struct {
 	sequence   []string
-	buffer     *bytes.Buffer
+	buffer     *bytes.Reader
 	index      int
 	refillFunc func(hash string) []byte
 }
 
+func NewSequenceReader(sequence []string, refillFunc func(hash string) []byte) *sequenceReader {
+	newData := refillFunc(sequence[0])
+	return &sequenceReader{
+		sequence:   sequence,
+		buffer:     bytes.NewReader(newData),
+		index:      1,
+		refillFunc: refillFunc,
+	}
+}
+
 // Read reads a new chunk using the refill function when there is no more data in the buffer
 func (reader *sequenceReader) Read(data []byte) (n int, err error) {
-	if len(reader.buffer.Bytes()) == 0 {
+	if reader.buffer.Len() == 0 {
 		if reader.index < len(reader.sequence) {
 			newData := reader.refillFunc(reader.sequence[reader.index])
-			reader.buffer.Write(newData)
+			reader.buffer = bytes.NewReader(newData)
 			reader.index++
 		} else {
 			return 0, io.EOF
@@ -269,6 +279,16 @@ func (reader *sequenceReader) Read(data []byte) (n int, err error) {
 	return reader.buffer.Read(data)
 }
 
+func (reader *sequenceReader) GetFirstByte() byte {
+	b, err := reader.buffer.ReadByte()
+	reader.buffer.UnreadByte()
+	if err != nil {
+		return 0
+	} else {
+		return b
+	}
+}
+
 func (manager *SnapshotManager) CreateChunkOperator(resurrect bool, rewriteChunks bool, threads int, allowFailures bool) {
 	if manager.chunkOperator == nil {
 		manager.chunkOperator = CreateChunkOperator(manager.config, manager.storage, manager.snapshotCache, resurrect, rewriteChunks, threads, allowFailures)