Always load the tree before getting the root.

The case where this is necessary is when we have zero merge
secondaries and thus no merge_backup processes loading the tree for
us.

1 files changed, 6 insertions, 3 deletions

diff --git a/merge/src/merge_sth.erl b/merge/src/merge_sth.erl
index 3dffaca..9e9486c 100644
--- a/merge/src/merge_sth.erl
+++ b/merge/src/merge_sth.erl
@@ -81,7 +81,7 @@ do_make_sth(Size) ->
     %% verify both the new sth file against the signature and the new
     %% root against ht before writing to disk.
     NewTimestamp = plop:generate_timestamp(),
-    NewRoot = ht:root(Size - 1),
+    NewRoot = root(Size),
     PackedSignature = make_signature(NewTimestamp, Size, NewRoot),
     ok = case plop:verify_sth(Size, NewTimestamp, NewRoot, PackedSignature) of
              true ->
@@ -134,8 +134,7 @@ verified_size(Path) ->
     end.
     
 validate_tree_head(Treesize, Roothash) ->
-    ht:load_tree(Treesize - 1),
-    ok = case ht:root(Treesize - 1) of
+    ok = case root(Treesize) of
              Roothash ->
                  ok;
              RoothashInTree ->
@@ -155,3 +154,7 @@ read_sth_treesize() ->
             true = plop:verify_sth(Treesize, Timestamp, RootHash, Signature),
             Treesize
     end.
+
+root(TreeSize) ->
+    ht:load_tree(TreeSize - 1),
+    ht:root(TreeSize - 1).