Test for data corruption in datafile decoding (#99)

* internal/data: move codec to own subpackage

* internal/data/codec: check & test nil Entry Decode

* internal/data/decoder: test for short prefix error

* internal/data/codec: test invalid key & value sizes

* internal/data/codec: check & test for truncated data

* interna/data/codec: use assert for tests

internal/data/codec/decoder_test.go

@@ -0,0 +1,109 @@
+package codec
+
+import (
+	"bytes"
+	"encoding/binary"
+	"io"
+	"testing"
+
+	"github.com/prologic/bitcask/internal"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestDecodeOnNilEntry(t *testing.T) {
+	t.Parallel()
+	assert := assert.New(t)
+	decoder := NewDecoder(&bytes.Buffer{}, 1, 1)
+
+	_, err := decoder.Decode(nil)
+	if assert.Error(err) {
+		assert.Equal(errCantDecodeOnNilEntry, err)
+	}
+}
+
+func TestShortPrefix(t *testing.T) {
+	t.Parallel()
+	assert := assert.New(t)
+	maxKeySize, maxValueSize := uint32(10), uint64(20)
+	prefix := make([]byte, keySize+valueSize)
+	binary.BigEndian.PutUint32(prefix, 1)
+	binary.BigEndian.PutUint64(prefix[keySize:], 1)
+
+	truncBytesCount := 2
+	buf := bytes.NewBuffer(prefix[:keySize+valueSize-truncBytesCount])
+	decoder := NewDecoder(buf, maxKeySize, maxValueSize)
+	_, err := decoder.Decode(&internal.Entry{})
+	if assert.Error(err) {
+		assert.Equal(io.ErrUnexpectedEOF, err)
+	}
+}
+
+func TestInvalidValueKeySizes(t *testing.T) {
+	assert := assert.New(t)
+	maxKeySize, maxValueSize := uint32(10), uint64(20)
+
+	tests := []struct {
+		keySize   uint32
+		valueSize uint64
+		name      string
+	}{
+		{keySize: 0, valueSize: 5, name: "zero key size"}, //zero value size is correct for tombstones
+		{keySize: 11, valueSize: 5, name: "key size overflow"},
+		{keySize: 5, valueSize: 21, name: "value size overflow"},
+		{keySize: 11, valueSize: 21, name: "key and value size overflow"},
+	}
+
+	for i := range tests {
+		i := i
+		t.Run(tests[i].name, func(t *testing.T) {
+			t.Parallel()
+			prefix := make([]byte, keySize+valueSize)
+			binary.BigEndian.PutUint32(prefix, tests[i].keySize)
+			binary.BigEndian.PutUint64(prefix[keySize:], tests[i].valueSize)
+
+			buf := bytes.NewBuffer(prefix)
+			decoder := NewDecoder(buf, maxKeySize, maxValueSize)
+			_, err := decoder.Decode(&internal.Entry{})
+			if assert.Error(err) {
+				assert.Equal(errInvalidKeyOrValueSize, err)
+			}
+		})
+	}
+}
+
+func TestTruncatedData(t *testing.T) {
+	assert := assert.New(t)
+	maxKeySize, maxValueSize := uint32(10), uint64(20)
+
+	key := []byte("foo")
+	value := []byte("bar")
+	data := make([]byte, keySize+valueSize+len(key)+len(value)+checksumSize)
+
+	binary.BigEndian.PutUint32(data, uint32(len(key)))
+	binary.BigEndian.PutUint64(data[keySize:], uint64(len(value)))
+	copy(data[keySize+valueSize:], key)
+	copy(data[keySize+valueSize+len(key):], value)
+	copy(data[keySize+valueSize+len(key)+len(value):], bytes.Repeat([]byte("0"), checksumSize))
+
+	tests := []struct {
+		data []byte
+		name string
+	}{
+		{data: data[:keySize+valueSize+len(key)-1], name: "truncated key"},
+		{data: data[:keySize+valueSize+len(key)+len(value)-1], name: "truncated value"},
+		{data: data[:keySize+valueSize+len(key)+len(value)+checksumSize-1], name: "truncated checksum"},
+	}
+
+	for i := range tests {
+		i := i
+		t.Run(tests[i].name, func(t *testing.T) {
+			t.Parallel()
+			buf := bytes.NewBuffer(tests[i].data)
+			decoder := NewDecoder(buf, maxKeySize, maxValueSize)
+			_, err := decoder.Decode(&internal.Entry{})
+			if assert.Error(err) {
+				assert.Equal(errTruncatedData, err)
+			}
+		})
+	}
+}