Rewrite the backup procedure to reduce memory usage

Main changes:

* Change the listing order of files/directories so that the local and remote
  snapshots can be compared on-the-fly.

* Introduce a new struct called EntryList that maintains a list of
  files/directories, which are kept in memory when the number is lower, and
  serialized into a file when there are too many.

* EntryList can also be turned into an on-disk incomplete snapshot quickly,
  to support fast-resume on next run.

* ChunkOperator can now download and upload chunks, thus replacing original
  ChunkDownloader and ChunkUploader.  The new ChunkDownloader is only used
  to prefetch chunks during the restore operation.

src/duplicacy_entrylist_test.go

@@ -0,0 +1,179 @@
+// Copyright (c) Acrosync LLC. All rights reserved.
+// Free for personal use and commercial trial
+// Commercial use requires per-user licenses available from https://duplicacy.com
+
+package duplicacy
+
+import (
+	"os"
+	"path"
+	"time"
+	"testing"
+	"math/rand"
+)
+
+
+func generateRandomString(length int) string {
+	var letters = []rune("abcdefghijklmnopqrstuvwxyz")
+    b := make([]rune, length)
+    for i := range b {
+        b[i] = letters[rand.Intn(len(letters))]
+    }
+    return string(b)
+}
+
+var fileSizeGenerator = rand.NewZipf(rand.New(rand.NewSource(time.Now().UnixNano())), 1.2, 1.0, 1024)
+
+func generateRandomFileSize() int64 {
+	return int64(fileSizeGenerator.Uint64() + 1)
+}
+
+func generateRandomChunks(totalFileSize int64) (chunks []string, lengths []int) {
+
+	totalChunkSize := int64(0)
+
+	for totalChunkSize < totalFileSize {
+		chunks = append(chunks, generateRandomString(64))
+		chunkSize := int64(1 + (rand.Int() % 64))
+		if chunkSize + totalChunkSize > totalFileSize {
+			chunkSize = totalFileSize - totalChunkSize
+		}
+		lengths = append(lengths, int(chunkSize))
+		totalChunkSize += chunkSize
+	}
+	return chunks, lengths
+
+}
+
+func getPreservedChunks(entries []*Entry, chunks []string, lengths []int) (preservedChunks []string, preservedChunkLengths []int) {
+	lastPreservedChunk := -1
+	for i := range entries {
+		if entries[i].Size < 0 {
+			continue
+		}
+		delta := entries[i].StartChunk - len(chunks)
+		if lastPreservedChunk != entries[i].StartChunk {
+			lastPreservedChunk = entries[i].StartChunk
+			preservedChunks = append(preservedChunks, chunks[entries[i].StartChunk])
+			preservedChunkLengths = append(preservedChunkLengths, lengths[entries[i].StartChunk])
+			delta++
+		}
+		for j := entries[i].StartChunk + 1; i <= entries[i].EndChunk; i++ {
+			preservedChunks = append(preservedChunks, chunks[j])
+			preservedChunkLengths = append(preservedChunkLengths, lengths[j])
+			lastPreservedChunk = j
+		}
+	}
+
+	return
+}
+
+func testEntryList(t *testing.T, numberOfEntries int, maximumInMemoryEntries int) {
+
+	entries := make([]*Entry, 0, numberOfEntries)
+	entrySizes := make([]int64, 0)
+
+	for i := 0; i < numberOfEntries; i++ {
+		entry:= CreateEntry(generateRandomString(16), -1, 0, 0700)
+		entries = append(entries, entry)
+		entrySizes = append(entrySizes, generateRandomFileSize())
+	}
+
+	totalFileSize := int64(0)
+	for _, size := range entrySizes {
+		totalFileSize += size
+	}
+
+	testDir := path.Join(os.TempDir(), "duplicacy_test")
+	os.RemoveAll(testDir)
+	os.MkdirAll(testDir, 0700)
+
+	os.MkdirAll(testDir + "/list1", 0700)
+	os.MkdirAll(testDir + "/list2", 0700)
+	os.MkdirAll(testDir + "/list3", 0700)
+	os.MkdirAll(testDir + "/list1", 0700)
+
+	// For the first entry list, all entries are new
+	entryList, _ := CreateEntryList("test", testDir + "/list1", maximumInMemoryEntries)
+	for _, entry := range entries {
+		entryList.AddEntry(entry)
+	}
+	uploadedChunks, uploadedChunksLengths := generateRandomChunks(totalFileSize)
+	for i, chunk := range uploadedChunks {
+		entryList.AddUploadedChunk(i, chunk, uploadedChunksLengths[i])
+	}
+
+	for i := range entryList.ModifiedEntries {
+		entryList.ModifiedEntries[i].Size = entrySizes[i]
+	}
+
+	totalEntries := 0
+	err := entryList.ReadEntries(func(entry *Entry) error {
+		totalEntries++
+		return nil
+	})
+
+	if err != nil {
+		t.Errorf("ReadEntries returned an error: %s", err)
+		return
+	}
+
+	if totalEntries != numberOfEntries {
+		t.Errorf("EntryList contains %d entries instead of %d", totalEntries, numberOfEntries)
+		return
+	}
+
+	// For the second entry list, half of the entries are new
+	for i := range entries {
+		if rand.Int() % 1 == 0 {
+			entries[i].Size = -1
+		} else {
+			entries[i].Size = entrySizes[i]
+		}
+	}
+
+	preservedChunks, preservedChunkLengths := getPreservedChunks(entries, uploadedChunks, uploadedChunksLengths)
+	entryList, _ = CreateEntryList("test", testDir + "/list2", maximumInMemoryEntries)
+	for _, entry := range entries {
+		entryList.AddEntry(entry)
+	}
+	for i, chunk := range preservedChunks {
+		entryList.AddPreservedChunk(chunk, preservedChunkLengths[i])
+	}
+
+	totalFileSize = 0
+	for i := range entryList.ModifiedEntries {
+		fileSize := generateRandomFileSize()		
+		entryList.ModifiedEntries[i].Size = fileSize
+		totalFileSize += fileSize
+	}
+
+	uploadedChunks, uploadedChunksLengths = generateRandomChunks(totalFileSize)
+	for i, chunk := range uploadedChunks {
+		entryList.AddUploadedChunk(i, chunk, uploadedChunksLengths[i])
+	}
+
+	totalEntries = 0
+	err = entryList.ReadEntries(func(entry *Entry) error {
+		totalEntries++
+		return nil
+	})
+
+	if err != nil {
+		t.Errorf("ReadEntries returned an error: %s", err)
+		return
+	}
+
+	if totalEntries != numberOfEntries {
+		t.Errorf("EntryList contains %d entries instead of %d", totalEntries, numberOfEntries)
+		return
+	}
+
+}
+
+
+func TestEntryList(t *testing.T) {
+	testEntryList(t, 1024, 1024)
+	testEntryList(t, 1024, 512)
+	testEntryList(t, 1024, 0)
+}