_filebaseddirectory.py: Fix encoding in open_file() for binary files

Python doesn't ignore `encoding` for binary files, it must be `None`.

1 files changed, 7 insertions, 2 deletions

diff --git a/src/buildstream/storage/_filebaseddirectory.py b/src/buildstream/storage/_filebaseddirectory.py
index 53a87b64c..1500dd78e 100644
--- a/src/buildstream/storage/_filebaseddirectory.py
+++ b/src/buildstream/storage/_filebaseddirectory.py
@@ -256,10 +256,15 @@ class FileBasedDirectory(Directory):
         if mode not in ["r", "rb", "w", "wb", "x", "xb"]:
             raise ValueError("Unsupported mode: `{}`".format(mode))
 
+        if "b" in mode:
+            encoding = None
+        else:
+            encoding = "utf-8"
+
         if "r" in mode:
-            return open(newpath, mode=mode, encoding="utf-8")
+            return open(newpath, mode=mode, encoding=encoding)
         else:
-            return utils.save_file_atomic(newpath, mode=mode, encoding="utf-8")
+            return utils.save_file_atomic(newpath, mode=mode, encoding=encoding)
 
     def __str__(self):
         # This returns the whole path (since we don't know where the directory started)