Add Digest type implementing TextMarshaler

This adds `type Digest []byte` for representing the result of a hash function.

This new type implements the Stringer and TextMarshaler interfaces so that the digest value is represented as a hexadecimal string.

auditbeat/module/file_integrity/action.go

@@ -83,6 +83,9 @@ func (action Action) String() string {
 	return strings.Join(list, "|")
 }
 
+// MarshalText marshals the Action to a textual representation of itself.
+func (action Action) MarshalText() ([]byte, error) { return []byte(action.String()), nil }
+
 func resolveActionOrder(action Action, existedBefore, existsNow bool) ActionArray {
 	if action == None {
 		return nil

auditbeat/module/file_integrity/event.go

@@ -36,6 +36,9 @@ func (s Source) String() string {
 	return "unknown"
 }
 
+// MarshalText marshals the Source to a textual representation of itself.
+func (s Source) MarshalText() ([]byte, error) { return []byte(s.String()), nil }
+
 const (
 	// SourceScan identifies events triggerd by a file system scan.
 	SourceScan Source = iota
@@ -59,6 +62,9 @@ func (t Type) String() string {
 	return "unknown"
 }
 
+// MarshalText marshals the Type to a textual representation of itself.
+func (t Type) MarshalText() ([]byte, error) { return []byte(t.String()), nil }
+
 // Enum of possible file.Types.
 const (
 	UnknownType Type = iota // Typically seen in deleted notifications where the object is gone.
@@ -73,6 +79,17 @@ var typeNames = map[Type]string{
 	SymlinkType: "symlink",
 }
 
+// Digest is a output of a hash function.
+type Digest []byte
+
+// String returns the digest value in lower-case hexadecimal form.
+func (d Digest) String() string {
+	return hex.EncodeToString(d)
+}
+
+// MarshalText encodes the digest to a hexadecimal representation of itself.
+func (d Digest) MarshalText() ([]byte, error) { return []byte(d.String()), nil }
+
 // Event describe the filesystem change and includes metadata about the file.
 type Event struct {
 	Timestamp  time.Time           // Time of event.
@@ -81,7 +98,7 @@ type Event struct {
 	Info       *Metadata           // File metadata (if the file exists).
 	Source     Source              // Source of the event.
 	Action     Action              // Action (like created, updated).
-	Hashes     map[HashType][]byte // File hashes.
+	Hashes     map[HashType]Digest // File hashes.
 
 	// Metadata
 	rtt    time.Duration // Time taken to collect the info.
@@ -240,8 +257,8 @@ func buildMetricbeatEvent(e *Event, existedBefore bool) mb.Event {
 		}
 	}
 
-	for hashType, hash := range e.Hashes {
-		m[string(hashType)] = hex.EncodeToString(hash)
+	for hashType, digest := range e.Hashes {
+		m[string(hashType)] = digest
 	}
 
 	out := mb.Event{
@@ -319,7 +336,7 @@ func diffEvents(old, new *Event) (Action, bool) {
 	return result, result != None
 }
 
-func hashFile(name string, hashType ...HashType) (map[HashType][]byte, error) {
+func hashFile(name string, hashType ...HashType) (map[HashType]Digest, error) {
 	if len(hashType) == 0 {
 		return nil, nil
 	}
@@ -376,7 +393,7 @@ func hashFile(name string, hashType ...HashType) (map[HashType][]byte, error) {
 		return nil, errors.Wrap(err, "failed to calculate file hashes")
 	}
 
-	nameToHash := make(map[HashType][]byte, len(hashes))
+	nameToHash := make(map[HashType]Digest, len(hashes))
 	for i, h := range hashes {
 		nameToHash[hashType[i]] = h.Sum(nil)
 	}

auditbeat/module/file_integrity/event_test.go

@@ -31,7 +31,7 @@ func testEvent() *Event {
 			MTime:  testEventTime,
 			SetGID: true,
 		},
-		Hashes: map[HashType][]byte{
+		Hashes: map[HashType]Digest{
 			SHA1:   mustDecodeHex("abcd"),
 			SHA256: mustDecodeHex("1234"),
 		},
@@ -109,7 +109,7 @@ func TestDiffEvents(t *testing.T) {
 
 	t.Run("different hash values", func(t *testing.T) {
 		e := testEvent()
-		e.Hashes = map[HashType][]byte{
+		e.Hashes = map[HashType]Digest{
 			SHA1:   mustDecodeHex("ef"),
 			SHA256: mustDecodeHex("1234"),
 		}
@@ -121,7 +121,7 @@ func TestDiffEvents(t *testing.T) {
 
 	t.Run("updated hashes and metadata", func(t *testing.T) {
 		e := testEvent()
-		e.Hashes = map[HashType][]byte{
+		e.Hashes = map[HashType]Digest{
 			SHA1:   mustDecodeHex("ef"),
 			SHA256: mustDecodeHex("1234"),
 		}
@@ -154,7 +154,7 @@ func TestDiffEvents(t *testing.T) {
 func TestHashFile(t *testing.T) {
 	t.Run("valid hashes", func(t *testing.T) {
 		// Computed externally.
-		expectedHashes := map[HashType][]byte{
+		expectedHashes := map[HashType]Digest{
 			BLAKE2B_256: mustDecodeHex("0f0cc1f0ea4ef962d6a150ae0b77bc320b57ed24e1609b933fa2274484f59145"),
 			BLAKE2B_384: mustDecodeHex("b819d90f648da6effff2393acb1884d2638642b3524c329832c073c9364149fcdedb522914ef9c2c92f007a42366139a"),
 			BLAKE2B_512: mustDecodeHex("fc13029e8a5ce67ad5a70f0cc659a4b30df9d791b125835e434606c6127ee37ebbc8b216389682ddfa84380789db09f2535d2a9837454414ea3ff00ec0801150"),

auditbeat/module/file_integrity/flatbuffers.go

@@ -52,7 +52,7 @@ func fbEncodeEvent(b *flatbuffers.Builder, e *Event) []byte {
 	return b.FinishedBytes()
 }
 
-func fbWriteHash(b *flatbuffers.Builder, hashes map[HashType][]byte) flatbuffers.UOffsetT {
+func fbWriteHash(b *flatbuffers.Builder, hashes map[HashType]Digest) flatbuffers.UOffsetT {
 	if len(hashes) == 0 {
 		return 0
 	}
@@ -252,13 +252,13 @@ func fbDecodeMetadata(e *schema.Event) *Metadata {
 	return rtn
 }
 
-func fbDecodeHash(e *schema.Event) map[HashType][]byte {
+func fbDecodeHash(e *schema.Event) map[HashType]Digest {
 	hash := e.Hashes(nil)
 	if hash == nil {
 		return nil
 	}
 
-	rtn := map[HashType][]byte{}
+	rtn := map[HashType]Digest{}
 	for _, hashType := range validHashes {
 		var length int
 		var producer func(i int) int8