From 2dfcd23ea965de797e48db199c16587b4b52050c Mon Sep 17 00:00:00 2001
From: Jarek Kowalski <jaak@jkowalski.net>
Date: Wed, 2 Aug 2017 07:23:38 +0200
Subject: [PATCH] added hashcache database, based on BoltDB which caches
 results of computing ObjectID for any given os.FileInfo.

---
 internal/hashcache/hashcache_database.go | 158 +++++++++++++++++++++++
 1 file changed, 158 insertions(+)
 create mode 100644 internal/hashcache/hashcache_database.go

diff --git a/internal/hashcache/hashcache_database.go b/internal/hashcache/hashcache_database.go
new file mode 100644
index 000000000..50df49d7c
--- /dev/null
+++ b/internal/hashcache/hashcache_database.go
@@ -0,0 +1,158 @@
+// Package hashcache implements streaming cache of file hashes.
+package hashcache
+
+import (
+	"bytes"
+	"compress/gzip"
+	"crypto/sha1"
+	"encoding/hex"
+	"encoding/json"
+	"fmt"
+	"log"
+	"os"
+
+	"github.com/boltdb/bolt"
+	"github.com/kopia/kopia/repo"
+)
+
+const batchSize = 10
+
+var hashcacheBucket = []byte("hashcache")
+
+// DB is a databsase caching ObjectID computations for local files.
+type DB struct {
+	db *bolt.DB
+}
+
+// DirectoryInfo manages a set of hashes for all directory entries.
+type DirectoryInfo struct {
+	parent  *DB
+	dirty   bool
+	dirName string
+
+	previousFiles map[string]string
+	currentFiles  map[string]string
+}
+
+// NewHashCacheDB returns new hash cache database stored in a given file.
+func NewHashCacheDB(filename string) (*DB, error) {
+	db, err := bolt.Open(filename, 0600, nil)
+	if err != nil {
+		return nil, err
+	}
+
+	return &DB{db: db}, nil
+}
+
+func (h *DB) keyOf(dirName string) []byte {
+	o := sha1.New()
+	fmt.Fprintf(o, "%v", dirName)
+	return o.Sum(nil)
+}
+
+// OpenDir returns DirectoryInfo for a single local directory.
+// The caller is expected to call Lookup()/Set() for all entries in the directory before calling Save().
+func (h *DB) OpenDir(dirName string) DirectoryInfo {
+	var dhi DirectoryInfo
+
+	h.db.View(func(t *bolt.Tx) error {
+		b := t.Bucket(hashcacheBucket)
+		if b == nil {
+			return nil
+		}
+
+		v := b.Get(h.keyOf(dirName))
+		if v == nil {
+			return nil
+		}
+
+		gz, err := gzip.NewReader(bytes.NewReader(v))
+		if err != nil {
+			return nil
+		}
+
+		var files map[string]string
+
+		if err := json.NewDecoder(gz).Decode(&files); err != nil {
+			return nil
+		}
+
+		dhi.previousFiles = files
+
+		return nil
+	})
+
+	dhi.parent = h
+	dhi.dirName = dirName
+	dhi.currentFiles = make(map[string]string)
+
+	return dhi
+}
+
+func (hi *DirectoryInfo) keyOf(fi os.FileInfo) string {
+	h := sha1.New()
+	fmt.Fprintf(h, "%v/%v/%v @ %v", fi.ModTime().UnixNano(), int(fi.Mode()), fi.Size(), fi.Name())
+	return hex.EncodeToString(h.Sum(nil))
+}
+
+// Lookup fetches the ObjectID corresponding to the given FileInfo in a directory, if present.
+func (hi *DirectoryInfo) Lookup(fi os.FileInfo) (repo.ObjectID, bool) {
+	k := hi.keyOf(fi)
+	s, ok := hi.previousFiles[k]
+	if !ok {
+		return repo.NullObjectID, false
+	}
+
+	oid, err := repo.ParseObjectID(s)
+	if err != nil {
+		return repo.NullObjectID, false
+	}
+
+	hi.currentFiles[k] = s
+	return oid, true
+}
+
+// Set associates ObjectID with a FileInfo that will be persisted on Save().
+func (hi *DirectoryInfo) Set(fi os.FileInfo, oid repo.ObjectID) {
+	k := hi.keyOf(fi)
+	new := oid.String()
+	hi.currentFiles[k] = new
+	hi.dirty = true
+}
+
+// Save writes the current associations of FileInfo->ObjectID for the directory to the databsase.
+// Any entries for which neither Lookup() nor Set() has been called are assumed to be removed.
+func (hi *DirectoryInfo) Save() error {
+	if len(hi.previousFiles) == len(hi.currentFiles) && !hi.dirty {
+		return nil
+	}
+
+	var buf bytes.Buffer
+	gz := gzip.NewWriter(&buf)
+
+	if err := json.NewEncoder(gz).Encode(hi.currentFiles); err != nil {
+		return err
+	}
+	gz.Flush()
+
+	value := buf.Bytes()
+
+	err := hi.parent.db.Update(func(t *bolt.Tx) error {
+		b := t.Bucket(hashcacheBucket)
+		if b == nil {
+			var err error
+			b, err = t.CreateBucket(hashcacheBucket)
+			if err != nil {
+				return err
+			}
+		}
+
+		return b.Put(hi.parent.keyOf(hi.dirName), value)
+	})
+
+	if err != nil {
+		log.Printf("warning: failed to update hash cache: %v", err)
+	}
+
+	return nil
+}