_casbaseddirectory.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/_casbaseddirectory.py b/src/buildstream/storage/_casbaseddirectory.py
index d6c4a7813..ed6fe206c 100644
--- a/src/buildstream/storage/_casbaseddirectory.py
+++ b/src/buildstream/storage/_casbaseddirectory.py
@@ -736,18 +736,23 @@ class CasBasedDirectory(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:
             if not entry:
                 raise FileNotFoundError("{} not found in {}".format(path[-1], str(subdir)))
 
             # Read-only access, allow direct access to CAS object
-            with open(self.cas_cache.objpath(entry.digest), mode, encoding="utf-8") as f:
+            with open(self.cas_cache.objpath(entry.digest), mode, encoding=encoding) as f:
                 yield f
         else:
             if "x" in mode and entry:
                 raise FileExistsError("{} already exists in {}".format(path[-1], str(subdir)))
 
-            with utils._tempnamedfile(mode, encoding="utf-8", dir=self.cas_cache.tmpdir) as f:
+            with utils._tempnamedfile(mode, encoding=encoding, dir=self.cas_cache.tmpdir) as f:
                 yield f
                 # Import written temporary file into CAS
                 f.flush()