Make portalocker optional

Author: rayluo

.gitignore

@@ -334,3 +334,5 @@ ASALocalRun/
 .mfractor/
 
 .eggs/
+.env
+Session.vim

Dockerfile

@@ -1,6 +1,6 @@
 # TODO: Can this Dockerfile use multi-stage build?
 # Final size 690MB. (It would be 1.16 GB if started with python:3 as base)
-FROM python:3.12-slim
+FROM python:3.13-slim
 
 # Install Generic PyGObject (sans GTK)
 #The following somehow won't work:
@@ -9,7 +9,6 @@ RUN apt-get update && apt-get install -y \
   libcairo2-dev \
   libgirepository1.0-dev \
   python3-dev
-RUN pip install "pygobject>=3,<4"
 
 # Install MSAL Extensions dependencies
 # Don't know how to get container talk to dbus on host,
@@ -19,10 +18,10 @@ RUN apt-get install -y \
   gnome-keyring
 
 # Not strictly necessary, but we include a pytest (which is only 3MB) to facilitate testing.
-RUN pip install "pytest>=6,<7"
+RUN pip install "pygobject>=3,<4" "pytest>=6,<7"
 
 # Install MSAL Extensions. Upgrade the pinned version number to trigger a new image build.
-RUN pip install "msal-extensions==1.1"
+RUN pip install "msal-extensions==1.2"
 
 # This setup is inspired from https://github.com/jaraco/keyring#using-keyring-on-headless-linux-systems-in-a-docker-container
 ENTRYPOINT ["dbus-run-session", "--"]

docker_run.sh

@@ -6,11 +6,10 @@ docker build -t $IMAGE_NAME - < Dockerfile
 echo "==== Integration Test for Persistence on Linux (libsecret) ===="
 echo "After seeing the bash prompt, run the following to test encryption on Linux:"
 echo "    pip install -e ."
-echo "    pytest -s tests/chosen_test_file.py"
-echo "Note that you probably need to set up ENV VAR for the test cases to run"
+echo "    pytest --capture=no -s tests/chosen_test_file.py"
+echo "Note: It will test portalocker-based lock when portalocker is installed, or test file-based lock otherwise."
 docker run --rm -it \
     --privileged \
-    --env-file .env \
     -w /home -v $PWD:/home \
     $IMAGE_NAME \
     $1

msal_extensions/__init__.py

@@ -8,6 +8,5 @@
     KeychainPersistence,
     LibsecretPersistence,
     )
-from .cache_lock import CrossPlatLock
-from .token_cache import PersistedTokenCache
+from .token_cache import PersistedTokenCache, CrossPlatLock, LockError
 

msal_extensions/cache_lock.py

@@ -5,12 +5,15 @@
 import time
 import logging
 
-import portalocker
+import portalocker  # pylint: disable=import-error
 
 
 logger = logging.getLogger(__name__)
 
 
+LockError = portalocker.exceptions.LockException
+
+
 class CrossPlatLock(object):
     """Offers a mechanism for waiting until another process is finished interacting with a shared
     resource. This is specifically written to interact with a class of the same name in the .NET

msal_extensions/filelock.py

@@ -0,0 +1,62 @@
+"""A cross-process lock based on exclusive creation of a given file name"""
+import os
+import sys
+import errno
+import time
+import logging
+
+
+logger = logging.getLogger(__name__)
+
+
+class LockError(RuntimeError):
+    """It will be raised when unable to obtain a lock"""
+
+
+class CrossPlatLock(object):
+    """This implementation relies only on ``open(..., 'x')``"""
+    def __init__(self, lockfile_path):
+        self._lockpath = lockfile_path
+
+    def __enter__(self):
+        self._create_lock_file('{} {}'.format(
+            os.getpid(),
+            sys.argv[0],
+            ).encode('utf-8'))  # pylint: disable=consider-using-f-string
+        return self
+
+    def _create_lock_file(self, content):
+        timeout = 5
+        check_interval = 0.25
+        current_time = getattr(time, "monotonic", time.time)
+        timeout_end = current_time() + timeout
+        while timeout_end > current_time():
+            try:
+                with open(self._lockpath, 'xb') as lock_file:  # pylint: disable=unspecified-encoding
+                    lock_file.write(content)
+                return None  # Happy path
+            except ValueError:  # This needs to be the first clause, for Python 2 to hit it
+                raise LockError("Python 2 does not support atomic creation of file")
+            except FileExistsError:  # Only Python 3 will reach this clause
+                logger.debug(
+                    "Process %d found existing lock file, will retry after %f second",
+                    os.getpid(), check_interval)
+                time.sleep(check_interval)
+        raise LockError(
+            "Unable to obtain lock, despite trying for {} second(s). "
+            "You may want to manually remove the stale lock file {}".format(
+                timeout,
+                self._lockpath,
+            ))
+
+    def __exit__(self, *args):
+        try:
+            os.remove(self._lockpath)
+        except OSError as ex:  # pylint: disable=invalid-name
+            if ex.errno in (errno.ENOENT, errno.EACCES):
+                # Probably another process has raced this one
+                # and ended up clearing or locking the file for itself.
+                logger.debug("Unable to remove lock file")
+            else:
+                raise
+

msal_extensions/token_cache.py

@@ -5,7 +5,10 @@
 
 import msal
 
-from .cache_lock import CrossPlatLock
+try:
+    from .cache_lock import CrossPlatLock, LockError  # It needs portalocker
+except ImportError:  # Falls back to file-based lock
+    from .filelock import CrossPlatLock, LockError  # It uses plain file
 from .persistence import _mkdir_p, PersistenceNotFound
 
 

setup.py

@@ -20,10 +20,14 @@
     python_requires=">=3.7",
     install_requires=[
         'msal>=1.29,<2',  # Use TokenCache.search() from MSAL Python 1.29+
-        'portalocker<3,>=1.4',
 
         ## We choose to NOT define a hard dependency on this.
         # "pygobject>=3,<4;platform_system=='Linux'",
     ],
+    extras_require={
+        "portalocker": [
+            'portalocker<3,>=1.4',
+        ],
+    },
     tests_require=['pytest'],
 )

tests/__init__.py

@@ -14,9 +14,10 @@
 import sys
 import time
 
-from portalocker import exceptions
+from msal_extensions import FilePersistence, CrossPlatLock, LockError
 
-from msal_extensions import FilePersistence, CrossPlatLock
+
+print("Testing with {}".format(CrossPlatLock))
 
 
 def _acquire_lock_and_write_to_cache(cache_location, sleep_interval):
@@ -31,7 +32,7 @@ def _acquire_lock_and_write_to_cache(cache_location, sleep_interval):
             time.sleep(sleep_interval)
             data += "> " + str(os.getpid()) + "\n"
             cache_accessor.save(data)
-    except exceptions.LockException as e:
+    except LockError as e:
         logging.warning("Unable to acquire lock %s", e)