From f02d9ad52b4b70fc1af8224201cf993faa82eaee Mon Sep 17 00:00:00 2001
From: Rasmus Dahlberg <rasmus.dahlberg@kau.se>
Date: Tue, 17 Nov 2020 12:11:30 +0100
Subject: fixed redundant tree head checking

---
 handler.go       | 10 ++++------
 trillian.go      |  9 ++++-----
 trillian_test.go |  3 +--
 type.go          | 14 ++++++--------
 4 files changed, 15 insertions(+), 21 deletions(-)

diff --git a/handler.go b/handler.go
index fe93f4f..d77379d 100644
--- a/handler.go
+++ b/handler.go
@@ -9,6 +9,7 @@ import (
 
 	"github.com/golang/glog"
 	"github.com/google/trillian"
+	"github.com/google/trillian/types"
 )
 
 // handler implements the http.Handler interface, and contains a reference
@@ -180,15 +181,12 @@ func getSth(ctx context.Context, i *Instance, w http.ResponseWriter, _ *http.Req
 	trsp, err := i.Client.GetLatestSignedLogRoot(ctx, &trillian.GetLatestSignedLogRootRequest{
 		LogId: i.LogParameters.TreeId,
 	})
-	if status, errInner := checkGetLatestSignedLogRoot(i.LogParameters, trsp, err); errInner != nil {
+	var lr types.LogRootV1
+	if status, errInner := checkGetLatestSignedLogRoot(i.LogParameters, trsp, err, &lr); errInner != nil {
 		return status, fmt.Errorf("bad GetLatestSignedLogRootResponse: %v", errInner)
 	}
 
-	th, err := NewTreeHeadV1(i.LogParameters, trsp.SignedLogRoot)
-	if err != nil {
-		return http.StatusInternalServerError, fmt.Errorf("failed creating tree head: %v", err)
-	}
-	sth, err := i.LogParameters.genV1Sth(th)
+	sth, err := i.LogParameters.genV1Sth(NewTreeHeadV1(i.LogParameters, &lr))
 	if err != nil {
 		return http.StatusInternalServerError, fmt.Errorf("failed creating signed tree head: %v", err)
 	}
diff --git a/trillian.go b/trillian.go
index 02b220c..8ae96a1 100644
--- a/trillian.go
+++ b/trillian.go
@@ -62,16 +62,15 @@ func checkGetConsistencyProof(lp *LogParameters, rsp *trillian.GetConsistencyPro
 	return checkHashPath(lp.HashType.Size(), rsp.Proof.Hashes)
 }
 
-func checkGetLatestSignedLogRoot(lp *LogParameters, rsp *trillian.GetLatestSignedLogRootResponse, err error) (int, error) {
+func checkGetLatestSignedLogRoot(lp *LogParameters, rsp *trillian.GetLatestSignedLogRootResponse, err error, out *types.LogRootV1) (int, error) {
 	if err != nil || rsp == nil || rsp.SignedLogRoot == nil || rsp.SignedLogRoot.LogRoot == nil {
 		return http.StatusInternalServerError, fmt.Errorf("%v", err)
 	}
-	var lr types.LogRootV1
-	if err := lr.UnmarshalBinary(rsp.SignedLogRoot.LogRoot); err != nil {
+	if err := out.UnmarshalBinary(rsp.SignedLogRoot.LogRoot); err != nil {
 		return http.StatusInternalServerError, fmt.Errorf("cannot unmarshal log root: %v", err)
 	}
-	if len(lr.RootHash) != lp.HashType.Size() {
-		return http.StatusInternalServerError, fmt.Errorf("invalid root hash: %v", lr.RootHash)
+	if len(out.RootHash) != lp.HashType.Size() {
+		return http.StatusInternalServerError, fmt.Errorf("invalid root hash: %v", out.RootHash)
 	}
 	return 0, nil
 }
diff --git a/trillian_test.go b/trillian_test.go
index 66ad647..7b26bb9 100644
--- a/trillian_test.go
+++ b/trillian_test.go
@@ -1,8 +1,8 @@
 package stfe
 
 import (
-	"testing"
 	"fmt"
+	"testing"
 
 	"github.com/google/trillian"
 	"github.com/system-transparency/stfe/server/testdata"
@@ -31,7 +31,6 @@ func TestCheckGetConsistencyProof(t *testing.T) {
 func TestCheckGetLatestSignedLogRoot(t *testing.T) {
 }
 
-
 // makeTrillianQueueLeafResponse creates a valid trillian QueueLeafResponse
 // for a package `name` where the checksum is all zeros (32 bytes).  The pemKey
 // is a PEM-encoded ed25519 signing key, and pemChain its certificate chain.
diff --git a/type.go b/type.go
index 93022b7..7105eff 100644
--- a/type.go
+++ b/type.go
@@ -282,15 +282,13 @@ func NewChecksumV1(identifier []byte, checksum []byte) *StItem {
 
 // NewTreeHead creates a new TreeHeadV1 from a Trillian-signed log root without
 // verifying any signature.  In other words, Trillian <-> STFE must be trusted.
-func NewTreeHeadV1(lp *LogParameters, slr *trillian.SignedLogRoot) (*TreeHeadV1, error) {
-	var lr types.LogRootV1
-	if err := lr.UnmarshalBinary(slr.GetLogRoot()); err != nil {
-		return nil, fmt.Errorf("failed unmarshaling Trillian slr: %v", err)
+func NewTreeHeadV1(lp *LogParameters, lr *types.LogRootV1) *TreeHeadV1 {
+	return &TreeHeadV1{
+		uint64(lr.TimestampNanos / 1000 / 1000),
+		uint64(lr.TreeSize),
+		NodeHash{lr.RootHash},
+		nil,
 	}
-	if lp.HashType.Size() != len(lr.RootHash) {
-		return nil, fmt.Errorf("invalid Trillian root hash: %v", lr.RootHash)
-	}
-	return &TreeHeadV1{uint64(lr.TimestampNanos / 1000 / 1000), uint64(lr.TreeSize), NodeHash{lr.RootHash}, nil}, nil
 }
 
 // NewAppendix creates a new leaf Appendix for an X.509 chain and signature
-- 
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