From 8a195d75028b6986740fd9daa7cf421090a35f68 Mon Sep 17 00:00:00 2001
From: David Rheinsberg <david.rheinsberg@gmail.com>
Date: Thu, 7 May 2020 17:07:51 +0200
Subject: [PATCH] util/ctx: extract suppress_oserror()

Extract the `suppress_oserror()` function from the ObjectManager and
make it available as utility for other code as well.

This also adds a bunch of tests that verify it works as expected.
---
 osbuild/objectstore.py    | 17 ++--------------
 osbuild/util/ctx.py       | 35 +++++++++++++++++++++++++++++++
 test/mod/test_util_ctx.py | 43 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 80 insertions(+), 15 deletions(-)
 create mode 100644 osbuild/util/ctx.py
 create mode 100644 test/mod/test_util_ctx.py

diff --git a/osbuild/objectstore.py b/osbuild/objectstore.py
index 8624a670..6fe58eca 100644
--- a/osbuild/objectstore.py
+++ b/osbuild/objectstore.py
@@ -7,7 +7,7 @@ import tempfile
 import weakref
 from typing import Optional
 
-import osbuild.util.rmrf as rmrf
+from osbuild.util import ctx, rmrf
 from . import treesum
 
 
@@ -16,19 +16,6 @@ __all__ = [
 ]
 
 
-@contextlib.contextmanager
-def suppress_oserror(*errnos):
-    """A context manager that suppresses any OSError with an errno in `errnos`.
-
-    Like contextlib.suppress, but can differentiate between OSErrors.
-    """
-    try:
-        yield
-    except OSError as e:
-        if e.errno not in errnos:
-            raise e
-
-
 def mount(source, target, bind=True, ro=True, private=True, mode="0755"):
     options = []
     if bind:
@@ -145,7 +132,7 @@ class Object:
         self._check_readers()
         self._check_writer()
         self.init()
-        with suppress_oserror(errno.ENOTEMPTY, errno.EEXIST):
+        with ctx.suppress_oserror(errno.ENOTEMPTY, errno.EEXIST):
             os.rename(self._tree, destination)
         self.reset()
 
diff --git a/osbuild/util/ctx.py b/osbuild/util/ctx.py
new file mode 100644
index 00000000..68c8ff45
--- /dev/null
+++ b/osbuild/util/ctx.py
@@ -0,0 +1,35 @@
+"""ContextManager Utilities
+
+This module implements helpers around python context-managers, with-statements,
+and RAII. It is meant as a supplement to `contextlib` from the python standard
+library.
+"""
+
+import contextlib
+
+
+__all__ = [
+    "suppress_oserror",
+]
+
+
+@contextlib.contextmanager
+def suppress_oserror(*errnos):
+    """Suppress OSError Exceptions
+
+    This is an extension to `contextlib.suppress()` from the python standard
+    library. It catches any `OSError` exceptions and suppresses them. However,
+    it only catches the exceptions that match the specified error numbers.
+
+    Parameters
+    ----------
+    errnos
+        A list of error numbers to match on. If none are specified, this
+        function has no effect.
+    """
+
+    try:
+        yield
+    except OSError as e:
+        if e.errno not in errnos:
+            raise e
diff --git a/test/mod/test_util_ctx.py b/test/mod/test_util_ctx.py
new file mode 100644
index 00000000..0bc2e3cc
--- /dev/null
+++ b/test/mod/test_util_ctx.py
@@ -0,0 +1,43 @@
+#
+# Tests for the 'osbuild.util.ctx' module.
+#
+
+import errno
+import unittest
+
+from osbuild.util import ctx
+
+
+class TestUtilCtx(unittest.TestCase):
+    def test_suppress_oserror(self):
+        #
+        # Verify the `suppress_oserror()` function.
+        #
+
+        # Empty list and empty statement is a no-op.
+        with ctx.suppress_oserror():
+            pass
+
+        # Single errno matches raised errno.
+        with ctx.suppress_oserror(errno.EPERM):
+            raise OSError(errno.EPERM, "Operation not permitted")
+
+        # Many errnos match raised errno regardless of their order.
+        with ctx.suppress_oserror(errno.EPERM, errno.ENOENT, errno.ESRCH):
+            raise OSError(errno.EPERM, "Operation not permitted")
+        with ctx.suppress_oserror(errno.ENOENT, errno.EPERM, errno.ESRCH):
+            raise OSError(errno.EPERM, "Operation not permitted")
+        with ctx.suppress_oserror(errno.ENOENT, errno.ESRCH, errno.EPERM):
+            raise OSError(errno.EPERM, "Operation not permitted")
+
+        # Empty list re-raises exceptions.
+        with self.assertRaises(OSError):
+            with ctx.suppress_oserror():
+                raise OSError(errno.EPERM, "Operation not permitted")
+
+        # Non-matching lists re-raise exceptions.
+        with self.assertRaises(OSError):
+            with ctx.suppress_oserror(errno.ENOENT):
+                raise OSError(errno.EPERM, "Operation not permitted")
+            with ctx.suppress_oserror(errno.ENOENT, errno.ESRCH):
+                raise OSError(errno.EPERM, "Operation not permitted")