fixed unexpected reflect behavior

After tls.Unmarshal() an empty slice is not assigned the nil value, but rather
a slice of zero length.  It is in contrast to NewTreeHeadV1(), which assigns a
nil value.  Therefore, reflect.DeepEqual() considers them to be different.

Fixed by assigning an empty tree head extension as `make([]byte, 0)`,
and not looking for nil values but rather zero-length values with len().

Further read: "Note that a non-nil empty slice and a nil slice [...] are
not deeply equal." (https://golang.org/pkg/reflect/#DeepEqual).

3 files changed, 4 insertions, 16 deletions

diff --git a/crypto_test.go b/crypto_test.go
index cfbb0a8..75e530e 100644
--- a/crypto_test.go
+++ b/crypto_test.go
@@ -118,8 +118,8 @@ func TestGenV1Sth(t *testing.T) {
 		if got, want := sth.TreeHead.RootHash.Data, th.RootHash.Data; !bytes.Equal(got, want) {
 			t.Errorf("got root hash %X, wanted %X in test %q", got, want, table.description)
 		}
-		if sth.TreeHead.Extension != nil {
-			t.Errorf("got extensions %X, wanted nil in test %q", sth.TreeHead.Extension, table.description)
+		if len(sth.TreeHead.Extension) != 0 {
+			t.Errorf("got extensions %X, wanted none in test %q", sth.TreeHead.Extension, table.description)
 		}
 	}
 }
diff --git a/sth.go b/sth.go
index e251b98..5cf3413 100644
--- a/sth.go
+++ b/sth.go
@@ -1,7 +1,6 @@
 package stfe
 
 import (
-	"bytes"
 	"context"
 	"fmt"
 	"reflect"
@@ -91,21 +90,10 @@ func (s *ActiveSthSource) Cosigned(_ context.Context) (*StItem, error) {
 	return s.currSth, nil
 }
 
-func (a *SignedTreeHeadV1) Equals(b *SignedTreeHeadV1) bool {
-	return bytes.Equal(a.LogId, b.LogId) &&
-		bytes.Equal(a.Signature, b.Signature) &&
-		a.TreeHead.Timestamp == b.TreeHead.Timestamp &&
-		a.TreeHead.TreeSize == b.TreeHead.TreeSize &&
-		bytes.Equal(a.TreeHead.RootHash.Data, b.TreeHead.RootHash.Data) &&
-		bytes.Equal(a.TreeHead.Extension, b.TreeHead.Extension)
-		// TODO: why reflect.DeepEqual(a, b) gives a different result? Fixme.
-}
-
 func (s *ActiveSthSource) AddCosignature(_ context.Context, costh *StItem) error {
 	s.mutex.Lock()
 	defer s.mutex.Unlock()
-	//if !reflect.DeepEqual(s.nextSth.CosignedTreeHeadV1.SignedTreeHeadV1, costh.CosignedTreeHeadV1.SignedTreeHeadV1) {
-	if !(&s.nextSth.CosignedTreeHeadV1.SignedTreeHeadV1).Equals(&costh.CosignedTreeHeadV1.SignedTreeHeadV1) {
+    if !reflect.DeepEqual(s.nextSth.CosignedTreeHeadV1.SignedTreeHeadV1, costh.CosignedTreeHeadV1.SignedTreeHeadV1) {
 		return fmt.Errorf("cosignature covers a different tree head")
 	}
 	witness := costh.CosignedTreeHeadV1.SignatureV1[0].Namespace.String()
diff --git a/type.go b/type.go
index 72aeecc..db9ddc6 100644
--- a/type.go
+++ b/type.go
@@ -282,7 +282,7 @@ func NewTreeHeadV1(lr *types.LogRootV1) *TreeHeadV1 {
 		uint64(lr.TimestampNanos / 1000 / 1000),
 		uint64(lr.TreeSize),
 		NodeHash{lr.RootHash},
-		nil,
+		make([]byte, 0),
 	}
 }