Improves Test Coverage by covering error cases (#95)

* Add Unit  Test for testing a corrupted config

* Add Unit Test for testing errors from .Stats()

* Refactor  Datafile into an interface and add Unit Tests for testing Merge() errors

* Refactor indexer into an interface and add Unit Tests for .Close() errors

* Add Unit Tests for .Delete() errors

* Add Unit Tests for  testing Put/Get errors

* Add Unit Test for testing Open errors (bad path for example)

* Refactor out bitcask.writeConfig

* Add more tests for config errors

* Add unit test for options that might error

* Add more test cases for close errors

* Add test case for rotating datafiles

* Fix a possible data race in .Stats()

* Add test case for checksum errors

* Add test case for Sync errors with Put and WithSync enabled

* Refactor and use testify.mock for mocks and generate mocks for all interfaces

* Refactor TestCloseErrors

* Refactored TestDeleteErrors

* Refactored TestGetErrors

* Refactored TestPutErrors

* Refactored TestMergeErrors and fixed a bug with .Fold()

* Add test case for Scan() errors

* Apparently only Scan() can return nil Node()s?

Makefile

@@ -39,6 +39,9 @@ profile: build
 bench: build
 	@go test -v -benchmem -bench=. .
 
+mocks:
+	@mockery -all -case underscore -output ./internal/mocks -recursive
+
 test: build
 	@go test -v \
 		-cover -coverprofile=coverage.txt -covermode=atomic \

bitcask.go

@@ -50,9 +50,10 @@ type Bitcask struct {
 	config    *config.Config
 	options   []Option
 	path      string
-	curr      *data.Datafile
-	datafiles map[int]*data.Datafile
+	curr      data.Datafile
+	datafiles map[int]data.Datafile
 	trie      art.Tree
+	indexer   index.Indexer
 }
 
 // Stats is a struct returned by Stats() on an open Bitcask instance
@@ -65,18 +66,14 @@ type Stats struct {
 // Stats returns statistics about the database including the number of
 // data files, keys and overall size on disk of the data
 func (b *Bitcask) Stats() (stats Stats, err error) {
-	var size int64
-
-	size, err = internal.DirSize(b.path)
-	if err != nil {
+	if stats.Size, err = internal.DirSize(b.path); err != nil {
 		return
 	}
 
-	stats.Datafiles = len(b.datafiles)
 	b.mu.RLock()
+	stats.Datafiles = len(b.datafiles)
 	stats.Keys = b.trie.Size()
 	b.mu.RUnlock()
-	stats.Size = size
 
 	return
 }
@@ -90,16 +87,7 @@ func (b *Bitcask) Close() error {
 		os.Remove(b.Flock.Path())
 	}()
 
-	f, err := os.OpenFile(filepath.Join(b.path, "index"), os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0600)
-	if err != nil {
-		return err
-	}
-	defer f.Close()
-
-	if err := index.WriteIndex(b.trie, f); err != nil {
-		return err
-	}
-	if err := f.Sync(); err != nil {
+	if err := b.indexer.Save(b.trie, filepath.Join(b.path, "index")); err != nil {
 		return err
 	}
 
@@ -120,7 +108,7 @@ func (b *Bitcask) Sync() error {
 // Get retrieves the value of the given key. If the key is not found or an/I/O
 // error occurs a null byte slice is returned along with the error.
 func (b *Bitcask) Get(key []byte) ([]byte, error) {
-	var df *data.Datafile
+	var df data.Datafile
 
 	b.mu.RLock()
 	value, found := b.trie.Search(key)
@@ -238,12 +226,6 @@ func (b *Bitcask) Keys() chan []byte {
 
 		for it := b.trie.Iterator(); it.HasNext(); {
 			node, _ := it.Next()
-
-			// Skip the root node
-			if len(node.Key()) == 0 {
-				continue
-			}
-
 			ch <- node.Key()
 		}
 		close(ch)
@@ -255,18 +237,18 @@ func (b *Bitcask) Keys() chan []byte {
 // Fold iterates over all keys in the database calling the function `f` for
 // each key. If the function returns an error, no further keys are processed
 // and the error returned.
-func (b *Bitcask) Fold(f func(key []byte) error) error {
+func (b *Bitcask) Fold(f func(key []byte) error) (err error) {
 	b.mu.RLock()
 	defer b.mu.RUnlock()
 
 	b.trie.ForEach(func(node art.Node) bool {
-		if err := f(node.Key()); err != nil {
+		if err = f(node.Key()); err != nil {
 			return false
 		}
 		return true
 	})
 
-	return nil
+	return
 }
 
 func (b *Bitcask) put(key, value []byte) (int64, int64, error) {
@@ -298,14 +280,6 @@ func (b *Bitcask) put(key, value []byte) (int64, int64, error) {
 	return b.curr.Write(e)
 }
 
-func (b *Bitcask) writeConfig() error {
-	data, err := b.config.Encode()
-	if err != nil {
-		return err
-	}
-	return ioutil.WriteFile(filepath.Join(b.path, "config.json"), data, 0600)
-}
-
 func (b *Bitcask) reopen() error {
 	b.mu.Lock()
 	defer b.mu.Unlock()
@@ -320,7 +294,7 @@ func (b *Bitcask) reopen() error {
 		return err
 	}
 
-	datafiles := make(map[int]*data.Datafile, len(ids))
+	datafiles := make(map[int]data.Datafile, len(ids))
 
 	for _, id := range ids {
 		df, err := data.NewDatafile(b.path, id, true)
@@ -330,7 +304,7 @@ func (b *Bitcask) reopen() error {
 		datafiles[id] = df
 	}
 
-	t, found, err := index.ReadFromFile(b.path, b.config.MaxKeySize)
+	t, found, err := b.indexer.Load(filepath.Join(b.path, "index"), b.config.MaxKeySize)
 	if err != nil {
 		return err
 	}
@@ -469,8 +443,13 @@ func Open(path string, options ...Option) (*Bitcask, error) {
 		return nil, err
 	}
 
-	cfg, err = config.Decode(path)
-	if err != nil {
+	configPath := filepath.Join(path, "config.json")
+	if internal.Exists(configPath) {
+		cfg, err = config.Load(configPath)
+		if err != nil {
+			return nil, err
+		}
+	} else {
 		cfg = newDefaultConfig()
 	}
 
@@ -479,6 +458,7 @@ func Open(path string, options ...Option) (*Bitcask, error) {
 		config:  cfg,
 		options: options,
 		path:    path,
+		indexer: index.NewIndexer(),
 	}
 
 	for _, opt := range options {
@@ -496,7 +476,7 @@ func Open(path string, options ...Option) (*Bitcask, error) {
 		return nil, ErrDatabaseLocked
 	}
 
-	if err := bitcask.writeConfig(); err != nil {
+	if err := cfg.Save(configPath); err != nil {
 		return nil, err
 	}
 

bitcask_test.go

@@ -2,6 +2,7 @@ package bitcask
 
 import (
 	"bytes"
+	"errors"
 	"fmt"
 	"io/ioutil"
 	"os"
@@ -13,6 +14,14 @@ import (
 	"testing"
 
 	"github.com/stretchr/testify/assert"
+
+	"github.com/prologic/bitcask/internal"
+	"github.com/prologic/bitcask/internal/config"
+	"github.com/prologic/bitcask/internal/mocks"
+)
+
+var (
+	ErrMockError = errors.New("error: mock error")
 )
 
 type sortByteArrays [][]byte
@@ -195,6 +204,36 @@ func TestDeletedKeys(t *testing.T) {
 	})
 }
 
+func TestConfigErrors(t *testing.T) {
+	assert := assert.New(t)
+
+	t.Run("CorruptConfig", func(t *testing.T) {
+		testdir, err := ioutil.TempDir("", "bitcask")
+		assert.NoError(err)
+		defer os.RemoveAll(testdir)
+
+		db, err := Open(testdir)
+		assert.NoError(err)
+		assert.NoError(db.Close())
+
+		assert.NoError(ioutil.WriteFile(filepath.Join(testdir, "config.json"), []byte("foo bar baz"), 0600))
+
+		_, err = Open(testdir)
+		assert.Error(err)
+	})
+
+	t.Run("BadConfigPath", func(t *testing.T) {
+		testdir, err := ioutil.TempDir("", "bitcask")
+		assert.NoError(err)
+		defer os.RemoveAll(testdir)
+
+		assert.NoError(os.Mkdir(filepath.Join(testdir, "config.json"), 0700))
+
+		_, err = Open(testdir)
+		assert.Error(err)
+	})
+}
+
 func TestReIndex(t *testing.T) {
 	assert := assert.New(t)
 
@@ -450,6 +489,109 @@ func TestStats(t *testing.T) {
 	})
 }
 
+func TestStatsError(t *testing.T) {
+	var (
+		db  *Bitcask
+		err error
+	)
+
+	assert := assert.New(t)
+
+	testdir, err := ioutil.TempDir("", "bitcask")
+	assert.NoError(err)
+
+	t.Run("Setup", func(t *testing.T) {
+		t.Run("Open", func(t *testing.T) {
+			db, err = Open(testdir)
+			assert.NoError(err)
+		})
+
+		t.Run("Put", func(t *testing.T) {
+			err := db.Put([]byte("foo"), []byte("bar"))
+			assert.NoError(err)
+		})
+
+		t.Run("Get", func(t *testing.T) {
+			val, err := db.Get([]byte("foo"))
+			assert.NoError(err)
+			assert.Equal([]byte("bar"), val)
+		})
+
+		t.Run("Stats", func(t *testing.T) {
+			stats, err := db.Stats()
+			assert.NoError(err)
+			assert.Equal(stats.Datafiles, 0)
+			assert.Equal(stats.Keys, 1)
+		})
+
+		t.Run("FabricatedDestruction", func(t *testing.T) {
+			// This would never happen in reality :D
+			// Or would it? :)
+			err = os.RemoveAll(testdir)
+			assert.NoError(err)
+		})
+
+		t.Run("Stats", func(t *testing.T) {
+			_, err := db.Stats()
+			assert.Error(err)
+		})
+	})
+}
+
+func TestMaxDatafileSize(t *testing.T) {
+	var (
+		db  *Bitcask
+		err error
+	)
+
+	assert := assert.New(t)
+
+	testdir, err := ioutil.TempDir("", "bitcask")
+	assert.NoError(err)
+	defer os.RemoveAll(testdir)
+
+	t.Run("Setup", func(t *testing.T) {
+		t.Run("Open", func(t *testing.T) {
+			db, err = Open(testdir, WithMaxDatafileSize(32))
+			assert.NoError(err)
+		})
+
+		t.Run("Put", func(t *testing.T) {
+			err := db.Put([]byte("foo"), []byte("bar"))
+			assert.NoError(err)
+		})
+	})
+
+	t.Run("Put", func(t *testing.T) {
+		for i := 0; i < 10; i++ {
+			err := db.Put([]byte(fmt.Sprintf("key_%d", i)), []byte("bar"))
+			assert.NoError(err)
+		}
+	})
+
+	t.Run("Sync", func(t *testing.T) {
+		err = db.Sync()
+		assert.NoError(err)
+	})
+
+	t.Run("Get", func(t *testing.T) {
+		val, err := db.Get([]byte("foo"))
+		assert.NoError(err)
+		assert.Equal([]byte("bar"), val)
+
+		for i := 0; i < 10; i++ {
+			val, err = db.Get([]byte(fmt.Sprintf("key_%d", i)))
+			assert.NoError(err)
+			assert.Equal([]byte("bar"), val)
+		}
+	})
+
+	t.Run("Close", func(t *testing.T) {
+		err = db.Close()
+		assert.NoError(err)
+	})
+}
+
 func TestMerge(t *testing.T) {
 	var (
 		db  *Bitcask
@@ -514,6 +656,286 @@ func TestMerge(t *testing.T) {
 	})
 }
 
+func TestGetErrors(t *testing.T) {
+	assert := assert.New(t)
+
+	t.Run("ReadError", func(t *testing.T) {
+		testdir, err := ioutil.TempDir("", "bitcask")
+		assert.NoError(err)
+		defer os.RemoveAll(testdir)
+
+		db, err := Open(testdir, WithMaxDatafileSize(32))
+		assert.NoError(err)
+
+		err = db.Put([]byte("foo"), []byte("bar"))
+		assert.NoError(err)
+
+		mockDatafile := new(mocks.Datafile)
+		mockDatafile.On("FileID").Return(0)
+		mockDatafile.On("ReadAt", int64(0), int64(22)).Return(
+			internal.Entry{},
+			ErrMockError,
+		)
+		db.curr = mockDatafile
+
+		_, err = db.Get([]byte("foo"))
+		assert.Error(err)
+		assert.Equal(ErrMockError, err)
+	})
+
+	t.Run("ChecksumError", func(t *testing.T) {
+		testdir, err := ioutil.TempDir("", "bitcask")
+		assert.NoError(err)
+		defer os.RemoveAll(testdir)
+
+		db, err := Open(testdir, WithMaxDatafileSize(32))
+		assert.NoError(err)
+
+		err = db.Put([]byte("foo"), []byte("bar"))
+		assert.NoError(err)
+
+		mockDatafile := new(mocks.Datafile)
+		mockDatafile.On("FileID").Return(0)
+		mockDatafile.On("ReadAt", int64(0), int64(22)).Return(
+			internal.Entry{
+				Checksum: 0x0,
+				Key:      []byte("foo"),
+				Offset:   0,
+				Value:    []byte("bar"),
+			},
+			nil,
+		)
+		db.curr = mockDatafile
+
+		_, err = db.Get([]byte("foo"))
+		assert.Error(err)
+		assert.Equal(ErrChecksumFailed, err)
+	})
+
+}
+
+func TestPutErrors(t *testing.T) {
+	assert := assert.New(t)
+
+	t.Run("WriteError", func(t *testing.T) {
+		testdir, err := ioutil.TempDir("", "bitcask")
+		assert.NoError(err)
+
+		db, err := Open(testdir)
+		assert.NoError(err)
+
+		mockDatafile := new(mocks.Datafile)
+		mockDatafile.On("Size").Return(int64(0))
+		mockDatafile.On(
+			"Write",
+			internal.Entry{
+				Checksum: 0x76ff8caa,
+				Key:      []byte("foo"),
+				Offset:   0,
+				Value:    []byte("bar"),
+			},
+		).Return(int64(0), int64(0), ErrMockError)
+		db.curr = mockDatafile
+
+		err = db.Put([]byte("foo"), []byte("bar"))
+		assert.Error(err)
+		assert.Equal(ErrMockError, err)
+	})
+
+	t.Run("SyncError", func(t *testing.T) {
+		testdir, err := ioutil.TempDir("", "bitcask")
+		assert.NoError(err)
+		db, err := Open(testdir, WithSync(true))
+		assert.NoError(err)
+
+		mockDatafile := new(mocks.Datafile)
+		mockDatafile.On("Size").Return(int64(0))
+		mockDatafile.On(
+			"Write",
+			internal.Entry{
+				Checksum: 0x78240498,
+				Key:      []byte("bar"),
+				Offset:   0,
+				Value:    []byte("baz"),
+			},
+		).Return(int64(0), int64(0), nil)
+		mockDatafile.On("Sync").Return(ErrMockError)
+		db.curr = mockDatafile
+
+		err = db.Put([]byte("bar"), []byte("baz"))
+		assert.Error(err)
+		assert.Equal(ErrMockError, err)
+	})
+}
+
+func TestOpenErrors(t *testing.T) {
+	assert := assert.New(t)
+
+	t.Run("BadPath", func(t *testing.T) {
+		testdir, err := ioutil.TempDir("", "bitcask")
+		assert.NoError(err)
+		defer os.RemoveAll(testdir)
+
+		assert.NoError(ioutil.WriteFile(filepath.Join(testdir, "foo"), []byte("foo"), 0600))
+
+		_, err = Open(filepath.Join(testdir, "foo", "tmp.db"))
+		assert.Error(err)
+	})
+
+	t.Run("BadOption", func(t *testing.T) {
+		testdir, err := ioutil.TempDir("", "bitcask")
+		assert.NoError(err)
+		defer os.RemoveAll(testdir)
+
+		withBogusOption := func() Option {
+			return func(cfg *config.Config) error {
+				return errors.New("mocked error")
+			}
+		}
+
+		_, err = Open(testdir, withBogusOption())
+		assert.Error(err)
+	})
+}
+
+func TestCloseErrors(t *testing.T) {
+	assert := assert.New(t)
+
+	testdir, err := ioutil.TempDir("", "bitcask")
+	assert.NoError(err)
+	defer os.RemoveAll(testdir)
+
+	t.Run("CloseIndexError", func(t *testing.T) {
+		db, err := Open(testdir, WithMaxDatafileSize(32))
+		assert.NoError(err)
+
+		mockIndexer := new(mocks.Indexer)
+		mockIndexer.On("Save", db.trie, filepath.Join(db.path, "index")).Return(ErrMockError)
+		db.indexer = mockIndexer
+
+		err = db.Close()
+		assert.Error(err)
+		assert.Equal(ErrMockError, err)
+	})
+
+	t.Run("CloseDatafilesError", func(t *testing.T) {
+		db, err := Open(testdir, WithMaxDatafileSize(32))
+		assert.NoError(err)
+
+		mockDatafile := new(mocks.Datafile)
+		mockDatafile.On("Close").Return(ErrMockError)
+		db.datafiles[0] = mockDatafile
+
+		err = db.Close()
+		assert.Error(err)
+		assert.Equal(ErrMockError, err)
+	})
+
+	t.Run("CloseActiveDatafileError", func(t *testing.T) {
+		db, err := Open(testdir, WithMaxDatafileSize(32))
+		assert.NoError(err)
+
+		mockDatafile := new(mocks.Datafile)
+		mockDatafile.On("Close").Return(ErrMockError)
+		db.curr = mockDatafile
+
+		err = db.Close()
+		assert.Error(err)
+		assert.Equal(ErrMockError, err)
+	})
+}
+
+func TestDeleteErrors(t *testing.T) {
+	assert := assert.New(t)
+
+	t.Run("WriteError", func(t *testing.T) {
+		testdir, err := ioutil.TempDir("", "bitcask")
+		assert.NoError(err)
+		defer os.RemoveAll(testdir)
+
+		db, err := Open(testdir, WithMaxDatafileSize(32))
+		assert.NoError(err)
+
+		err = db.Put([]byte("foo"), []byte("bar"))
+		assert.NoError(err)
+
+		mockDatafile := new(mocks.Datafile)
+		mockDatafile.On("Size").Return(int64(0))
+		mockDatafile.On(
+			"Write",
+			internal.Entry{
+				Checksum: 0x0,
+				Key:      []byte("foo"),
+				Offset:   0,
+				Value:    []byte{},
+			},
+		).Return(int64(0), int64(0), ErrMockError)
+		db.curr = mockDatafile
+
+		err = db.Delete([]byte("foo"))
+		assert.Error(err)
+	})
+}
+
+func TestMergeErrors(t *testing.T) {
+	assert := assert.New(t)
+
+	t.Run("RemoveDatabaseDirectory", func(t *testing.T) {
+		testdir, err := ioutil.TempDir("", "bitcask")
+		assert.NoError(err)
+		defer os.RemoveAll(testdir)
+
+		db, err := Open(testdir, WithMaxDatafileSize(32))
+		assert.NoError(err)
+
+		assert.NoError(os.RemoveAll(testdir))
+
+		err = db.Merge()
+		assert.Error(err)
+	})
+
+	t.Run("EmptyCloseError", func(t *testing.T) {
+		testdir, err := ioutil.TempDir("", "bitcask")
+		assert.NoError(err)
+		defer os.RemoveAll(testdir)
+
+		db, err := Open(testdir)
+		assert.NoError(err)
+
+		mockDatafile := new(mocks.Datafile)
+		mockDatafile.On("Close").Return(ErrMockError)
+		db.curr = mockDatafile
+
+		err = db.Merge()
+		assert.Error(err)
+		assert.Equal(ErrMockError, err)
+	})
+
+	t.Run("ReadError", func(t *testing.T) {
+		testdir, err := ioutil.TempDir("", "bitcask")
+		assert.NoError(err)
+		defer os.RemoveAll(testdir)
+
+		db, err := Open(testdir)
+		assert.NoError(err)
+
+		assert.NoError(db.Put([]byte("foo"), []byte("bar")))
+
+		mockDatafile := new(mocks.Datafile)
+		mockDatafile.On("FileID").Return(0)
+		mockDatafile.On("ReadAt", int64(0), int64(22)).Return(
+			internal.Entry{},
+			ErrMockError,
+		)
+		db.curr = mockDatafile
+
+		err = db.Merge()
+		assert.Error(err)
+		assert.Equal(ErrMockError, err)
+	})
+
+}
+
 func TestConcurrent(t *testing.T) {
 	var (
 		db  *Bitcask
@@ -642,6 +1064,14 @@ func TestScan(t *testing.T) {
 		vals = SortByteArrays(vals)
 		assert.Equal(expected, vals)
 	})
+
+	t.Run("ScanErrors", func(t *testing.T) {
+		err = db.Scan([]byte("fo"), func(key []byte) error {
+			return ErrMockError
+		})
+		assert.Error(err)
+		assert.Equal(ErrMockError, err)
+	})
 }
 
 func TestLocking(t *testing.T) {

cmd/bitcask/recover.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"os"
+	"path/filepath"
 
 	"github.com/prologic/bitcask"
 	"github.com/prologic/bitcask/internal/config"
@@ -36,11 +37,11 @@ func init() {
 
 func recover(path string, dryRun bool) int {
 	maxKeySize := bitcask.DefaultMaxKeySize
-	if cfg, err := config.Decode(path); err == nil {
+	if cfg, err := config.Load(filepath.Join(path, "config.json")); err == nil {
 		maxKeySize = cfg.MaxKeySize
 	}
 
-	t, found, err := index.ReadFromFile(path, maxKeySize)
+	t, found, err := index.NewIndexer().Load(path, maxKeySize)
 	if err != nil && !index.IsIndexCorruption(err) {
 		log.WithError(err).Info("error while opening the index file")
 	}
@@ -60,24 +61,12 @@ func recover(path string, dryRun bool) int {
 		return 0
 	}
 
-	fi, err := os.OpenFile("index.recovered", os.O_WRONLY|os.O_CREATE, 0600)
-	if err != nil {
-		log.WithError(err).Info("error while creating recovered index file")
-		return 1
-	}
-
 	// Leverage that t has the partiatially read tree even on corrupted files
-	err = index.WriteIndex(t, fi)
+	err = index.NewIndexer().Save(t, "index.recovered")
 	if err != nil {
 		log.WithError(err).Info("error while writing the recovered index file")
-
-		fi.Close()
 		return 1
 	}
-	err = fi.Close()
-	if err != nil {
-		log.WithError(err).Info("the recovered file index coudn't be saved correctly")
-	}
 	log.Debug("the index was recovered in the index.recovered new file")
 
 	return 0

go.sum

@@ -116,6 +116,7 @@ github.com/spf13/viper v1.3.2/go.mod h1:ZiWeW+zYFKm7srdB9IoDzzZXaJaI5eL9QjNiN/DM
 github.com/spf13/viper v1.4.0 h1:yXHLWeravcrgGyFSyCgdYpXQ9dR9c/WED3pg1RhxqEU=
 github.com/spf13/viper v1.4.0/go.mod h1:PTJ7Z/lr49W6bUbkmS1V3by4uWynFiR9p7+dSq/yZzE=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/objx v0.1.1 h1:2vfRuCMp5sSVIDSqO8oNnWJq7mPa6KVP3iPIwFBuy8A=
 github.com/stretchr/objx v0.1.1/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
 github.com/stretchr/testify v1.2.2/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
 github.com/stretchr/testify v1.3.0 h1:TivCn/peBQ7UY8ooIcPgZFpTNSz0Q2U6UrFlUfqbe0Q=

internal/config/config.go

@@ -3,7 +3,7 @@ package config
 import (
 	"encoding/json"
 	"io/ioutil"
-	"path/filepath"
+	"os"
 )
 
 // Config contains the bitcask configuration parameters
@@ -14,11 +14,11 @@ type Config struct {
 	Sync            bool `json:"sync"`
 }
 
-// Decode decodes a serialized configuration
-func Decode(path string) (*Config, error) {
+// Load loads a configuration from the given path
+func Load(path string) (*Config, error) {
 	var cfg Config
 
-	data, err := ioutil.ReadFile(filepath.Join(path, "config.json"))
+	data, err := ioutil.ReadFile(path)
 	if err != nil {
 		return nil, err
 	}
@@ -30,7 +30,25 @@ func Decode(path string) (*Config, error) {
 	return &cfg, nil
 }
 
-// Encode encodes the configuration for storage
-func (c *Config) Encode() ([]byte, error) {
-	return json.Marshal(c)
+// Save saves the configuration to the provided path
+func (c *Config) Save(path string) error {
+	f, err := os.OpenFile(path, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0600)
+	if err != nil {
+		return err
+	}
+
+	data, err := json.Marshal(c)
+	if err != nil {
+		return err
+	}
+
+	if _, err = f.Write(data); err != nil {
+		return err
+	}
+
+	if err = f.Sync(); err != nil {
+		return err
+	}
+
+	return f.Close()
 }

internal/data/datafile.go

@@ -22,7 +22,18 @@ var (
 	mxMemPool sync.RWMutex
 )
 
-type Datafile struct {
+type Datafile interface {
+	FileID() int
+	Name() string
+	Close() error
+	Sync() error
+	Size() int64
+	Read() (internal.Entry, int64, error)
+	ReadAt(index, size int64) (internal.Entry, error)
+	Write(internal.Entry) (int64, int64, error)
+}
+
+type datafile struct {
 	sync.RWMutex
 
 	id     int
@@ -34,7 +45,7 @@ type Datafile struct {
 	enc    *Encoder
 }
 
-func NewDatafile(path string, id int, readonly bool) (*Datafile, error) {
+func NewDatafile(path string, id int, readonly bool) (Datafile, error) {
 	var (
 		r   *os.File
 		ra  *mmap.ReaderAt
@@ -70,7 +81,7 @@ func NewDatafile(path string, id int, readonly bool) (*Datafile, error) {
 	dec := NewDecoder(r)
 	enc := NewEncoder(w)
 
-	return &Datafile{
+	return &datafile{
 		id:     id,
 		r:      r,
 		ra:     ra,
@@ -81,21 +92,21 @@ func NewDatafile(path string, id int, readonly bool) (*Datafile, error) {
 	}, nil
 }
 
-func (df *Datafile) FileID() int {
+func (df *datafile) FileID() int {
 	return df.id
 }
 
-func (df *Datafile) Name() string {
+func (df *datafile) Name() string {
 	return df.r.Name()
 }
 
-func (df *Datafile) Close() error {
+func (df *datafile) Close() error {
 	defer func() {
 		df.ra.Close()
 		df.r.Close()
 	}()
 
-	// Readonly Datafile -- Nothing further to close on the write side
+	// Readonly datafile -- Nothing further to close on the write side
 	if df.w == nil {
 		return nil
 	}
@@ -107,20 +118,20 @@ func (df *Datafile) Close() error {
 	return df.w.Close()
 }
 
-func (df *Datafile) Sync() error {
+func (df *datafile) Sync() error {
 	if df.w == nil {
 		return nil
 	}
 	return df.w.Sync()
 }
 
-func (df *Datafile) Size() int64 {
+func (df *datafile) Size() int64 {
 	df.RLock()
 	defer df.RUnlock()
 	return df.offset
 }
 
-func (df *Datafile) Read() (e internal.Entry, n int64, err error) {
+func (df *datafile) Read() (e internal.Entry, n int64, err error) {
 	df.Lock()
 	defer df.Unlock()
 
@@ -132,7 +143,7 @@ func (df *Datafile) Read() (e internal.Entry, n int64, err error) {
 	return
 }
 
-func (df *Datafile) ReadAt(index, size int64) (e internal.Entry, err error) {
+func (df *datafile) ReadAt(index, size int64) (e internal.Entry, err error) {
 	var n int
 
 	b := make([]byte, size)
@@ -156,7 +167,7 @@ func (df *Datafile) ReadAt(index, size int64) (e internal.Entry, err error) {
 	return
 }
 
-func (df *Datafile) Write(e internal.Entry) (int64, int64, error) {
+func (df *datafile) Write(e internal.Entry) (int64, int64, error) {
 	if df.w == nil {
 		return -1, 0, ErrReadonly
 	}

internal/index/codec_index.go

@@ -108,8 +108,7 @@ func readIndex(r io.Reader, t art.Tree, maxKeySize int) error {
 	return nil
 }
 
-// WriteIndex persists a Tree into a io.Writer
-func WriteIndex(t art.Tree, w io.Writer) (err error) {
+func writeIndex(t art.Tree, w io.Writer) (err error) {
 	t.ForEach(func(node art.Node) bool {
 		err = writeBytes(node.Key(), w)
 		if err != nil {

internal/index/index.go

@@ -2,26 +2,55 @@ package index
 
 import (
 	"os"
-	"path"
 
 	art "github.com/plar/go-adaptive-radix-tree"
 	"github.com/prologic/bitcask/internal"
 )
 
-// ReadFromFile reads an index from a persisted file
-func ReadFromFile(filePath string, maxKeySize int) (art.Tree, bool, error) {
+type Indexer interface {
+	Load(path string, maxkeySize int) (art.Tree, bool, error)
+	Save(t art.Tree, path string) error
+}
+
+func NewIndexer() Indexer {
+	return &indexer{}
+}
+
+type indexer struct{}
+
+func (i *indexer) Load(path string, maxKeySize int) (art.Tree, bool, error) {
 	t := art.New()
-	if !internal.Exists(path.Join(filePath, "index")) {
+
+	if !internal.Exists(path) {
 		return t, false, nil
 	}
 
-	f, err := os.Open(path.Join(filePath, "index"))
+	f, err := os.Open(path)
 	if err != nil {
 		return t, true, err
 	}
 	defer f.Close()
+
 	if err := readIndex(f, t, maxKeySize); err != nil {
 		return t, true, err
 	}
 	return t, true, nil
 }
+
+func (i *indexer) Save(t art.Tree, path string) error {
+	f, err := os.OpenFile(path, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0600)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	if err := writeIndex(t, f); err != nil {
+		return err
+	}
+
+	if err := f.Sync(); err != nil {
+		return err
+	}
+
+	return f.Close()
+}

internal/mocks/datafile.go

@@ -0,0 +1,158 @@
+// Code generated by mockery v1.0.0. DO NOT EDIT.
+
+package mocks
+
+import internal "github.com/prologic/bitcask/internal"
+import mock "github.com/stretchr/testify/mock"
+
+// Datafile is an autogenerated mock type for the Datafile type
+type Datafile struct {
+	mock.Mock
+}
+
+// Close provides a mock function with given fields:
+func (_m *Datafile) Close() error {
+	ret := _m.Called()
+
+	var r0 error
+	if rf, ok := ret.Get(0).(func() error); ok {
+		r0 = rf()
+	} else {
+		r0 = ret.Error(0)
+	}
+
+	return r0
+}
+
+// FileID provides a mock function with given fields:
+func (_m *Datafile) FileID() int {
+	ret := _m.Called()
+
+	var r0 int
+	if rf, ok := ret.Get(0).(func() int); ok {
+		r0 = rf()
+	} else {
+		r0 = ret.Get(0).(int)
+	}
+
+	return r0
+}
+
+// Name provides a mock function with given fields:
+func (_m *Datafile) Name() string {
+	ret := _m.Called()
+
+	var r0 string
+	if rf, ok := ret.Get(0).(func() string); ok {
+		r0 = rf()
+	} else {
+		r0 = ret.Get(0).(string)
+	}
+
+	return r0
+}
+
+// Read provides a mock function with given fields:
+func (_m *Datafile) Read() (internal.Entry, int64, error) {
+	ret := _m.Called()
+
+	var r0 internal.Entry
+	if rf, ok := ret.Get(0).(func() internal.Entry); ok {
+		r0 = rf()
+	} else {
+		r0 = ret.Get(0).(internal.Entry)
+	}
+
+	var r1 int64
+	if rf, ok := ret.Get(1).(func() int64); ok {
+		r1 = rf()
+	} else {
+		r1 = ret.Get(1).(int64)
+	}
+
+	var r2 error
+	if rf, ok := ret.Get(2).(func() error); ok {
+		r2 = rf()
+	} else {
+		r2 = ret.Error(2)
+	}
+
+	return r0, r1, r2
+}
+
+// ReadAt provides a mock function with given fields: index, size
+func (_m *Datafile) ReadAt(index int64, size int64) (internal.Entry, error) {
+	ret := _m.Called(index, size)
+
+	var r0 internal.Entry
+	if rf, ok := ret.Get(0).(func(int64, int64) internal.Entry); ok {
+		r0 = rf(index, size)
+	} else {
+		r0 = ret.Get(0).(internal.Entry)
+	}
+
+	var r1 error
+	if rf, ok := ret.Get(1).(func(int64, int64) error); ok {
+		r1 = rf(index, size)
+	} else {
+		r1 = ret.Error(1)
+	}
+
+	return r0, r1
+}
+
+// Size provides a mock function with given fields:
+func (_m *Datafile) Size() int64 {
+	ret := _m.Called()
+
+	var r0 int64
+	if rf, ok := ret.Get(0).(func() int64); ok {
+		r0 = rf()
+	} else {
+		r0 = ret.Get(0).(int64)
+	}
+
+	return r0
+}
+
+// Sync provides a mock function with given fields:
+func (_m *Datafile) Sync() error {
+	ret := _m.Called()
+
+	var r0 error
+	if rf, ok := ret.Get(0).(func() error); ok {
+		r0 = rf()
+	} else {
+		r0 = ret.Error(0)
+	}
+
+	return r0
+}
+
+// Write provides a mock function with given fields: _a0
+func (_m *Datafile) Write(_a0 internal.Entry) (int64, int64, error) {
+	ret := _m.Called(_a0)
+
+	var r0 int64
+	if rf, ok := ret.Get(0).(func(internal.Entry) int64); ok {
+		r0 = rf(_a0)
+	} else {
+		r0 = ret.Get(0).(int64)
+	}
+
+	var r1 int64
+	if rf, ok := ret.Get(1).(func(internal.Entry) int64); ok {
+		r1 = rf(_a0)
+	} else {
+		r1 = ret.Get(1).(int64)
+	}
+
+	var r2 error
+	if rf, ok := ret.Get(2).(func(internal.Entry) error); ok {
+		r2 = rf(_a0)
+	} else {
+		r2 = ret.Error(2)
+	}
+
+	return r0, r1, r2
+}

internal/mocks/indexer.go

@@ -0,0 +1,56 @@
+// Code generated by mockery v1.0.0. DO NOT EDIT.
+
+package mocks
+
+import art "github.com/plar/go-adaptive-radix-tree"
+
+import mock "github.com/stretchr/testify/mock"
+
+// Indexer is an autogenerated mock type for the Indexer type
+type Indexer struct {
+	mock.Mock
+}
+
+// Load provides a mock function with given fields: path, maxkeySize
+func (_m *Indexer) Load(path string, maxkeySize int) (art.Tree, bool, error) {
+	ret := _m.Called(path, maxkeySize)
+
+	var r0 art.Tree
+	if rf, ok := ret.Get(0).(func(string, int) art.Tree); ok {
+		r0 = rf(path, maxkeySize)
+	} else {
+		if ret.Get(0) != nil {
+			r0 = ret.Get(0).(art.Tree)
+		}
+	}
+
+	var r1 bool
+	if rf, ok := ret.Get(1).(func(string, int) bool); ok {
+		r1 = rf(path, maxkeySize)
+	} else {
+		r1 = ret.Get(1).(bool)
+	}
+
+	var r2 error
+	if rf, ok := ret.Get(2).(func(string, int) error); ok {
+		r2 = rf(path, maxkeySize)
+	} else {
+		r2 = ret.Error(2)
+	}
+
+	return r0, r1, r2
+}
+
+// Save provides a mock function with given fields: t, path
+func (_m *Indexer) Save(t art.Tree, path string) error {
+	ret := _m.Called(t, path)
+
+	var r0 error
+	if rf, ok := ret.Get(0).(func(art.Tree, string) error); ok {
+		r0 = rf(t, path)
+	} else {
+		r0 = ret.Error(0)
+	}
+
+	return r0
+}