--- a/mercurial/commands.py
+++ b/mercurial/commands.py
@@ -283,7 +283,7 @@ def dodiff(fp, ui, repo, node1, node2, f
if not node1:
node1 = repo.dirstate.parents()[0]
def read(f):
- return repo.wfile(f).read()
+ return repo.wread(f)
if ui.quiet:
r = None