buildstream/_artifactcache/cascache.py

@@ -54,7 +54,6 @@ _MAX_PAYLOAD_BYTES = 1024 * 1024
 #
 # Args:
 #     context (Context): The BuildStream context
-#     enable_push (bool): Whether pushing is allowed by the platform
 #
 # Pushing is explicitly disabled by the platform in some cases,
 # like when we are falling back to functioning without using
@@ -62,7 +61,7 @@ _MAX_PAYLOAD_BYTES = 1024 * 1024
 #
 class CASCache(ArtifactCache):
 
-    def __init__(self, context, *, enable_push=True):
+    def __init__(self, context):
         super().__init__(context)
 
         self.casdir = os.path.join(context.artifactdir, 'cas')
@@ -71,8 +70,6 @@ class CASCache(ArtifactCache):
 
         self._calculate_cache_quota()
 
-        self._enable_push = enable_push
-
         # Per-project list of _CASRemote instances.
         self._remotes = {}
 
@@ -214,7 +211,7 @@ class CASCache(ArtifactCache):
             return bool(remotes_for_project)
 
     def has_push_remotes(self, *, element=None):
-        if not self._has_push_remotes or not self._enable_push:
+        if not self._has_push_remotes:
             # No project has push remotes
             return False
         elif element is None:

buildstream/_artifactcache/casserver.py

@@ -35,8 +35,6 @@ from .._protos.buildstream.v2 import buildstream_pb2, buildstream_pb2_grpc
 from .._exceptions import ArtifactError
 from .._context import Context
 
-from .cascache import CASCache
-
 
 # The default limit for gRPC messages is 4 MiB.
 # Limit payload to 1 MiB to leave sufficient headroom for metadata.
@@ -60,7 +58,7 @@ def create_server(repo, *, enable_push):
     context = Context()
     context.artifactdir = os.path.abspath(repo)
 
-    artifactcache = CASCache(context)
+    artifactcache = context.artifactcache
 
     # Use max_workers default from Python 3.5+
     max_workers = (os.cpu_count() or 1) * 5

buildstream/_context.py

@@ -30,6 +30,7 @@ from ._exceptions import LoadError, LoadErrorReason, BstError
 from ._message import Message, MessageType
 from ._profile import Topics, profile_start, profile_end
 from ._artifactcache import ArtifactCache
+from ._artifactcache.cascache import CASCache
 from ._workspaces import Workspaces
 from .plugin import _plugin_lookup
 
@@ -113,6 +114,7 @@ class Context():
         self._cache_key = None
         self._message_handler = None
         self._message_depth = deque()
+        self._artifactcache = None
         self._projects = []
         self._project_overrides = {}
         self._workspaces = None
@@ -227,6 +229,13 @@ class Context():
                             "{}: on-error should be one of: {}".format(
                                 provenance, ", ".join(valid_actions)))
 
+    @property
+    def artifactcache(self):
+        if not self._artifactcache:
+            self._artifactcache = CASCache(self)
+
+        return self._artifactcache
+
     # add_project():
     #
     # Add a project to the context.

buildstream/_frontend/app.py

@@ -115,14 +115,6 @@ class App():
         else:
             self.colors = False
 
-        # Increase the soft limit for open file descriptors to the maximum.
-        # SafeHardlinks FUSE needs to hold file descriptors for all processes in the sandbox.
-        # Avoid hitting the limit too quickly.
-        limits = resource.getrlimit(resource.RLIMIT_NOFILE)
-        if limits[0] != limits[1]:
-            # Set soft limit to hard limit
-            resource.setrlimit(resource.RLIMIT_NOFILE, (limits[1], limits[1]))
-
     # create()
     #
     # Should be used instead of the regular constructor.
@@ -198,7 +190,7 @@ class App():
             if option_value is not None:
                 setattr(self.context, context_attr, option_value)
         try:
-            Platform.create_instance(self.context)
+            Platform.get_platform()
         except BstError as e:
             self._error_exit(e, "Error instantiating platform")
 

buildstream/_loader/loader.py

@@ -28,7 +28,6 @@ from .. import Consistency
 from .. import _yaml
 from ..element import Element
 from .._profile import Topics, profile_start, profile_end
-from .._platform import Platform
 from .._includes import Includes
 
 from .types import Symbol, Dependency
@@ -518,8 +517,7 @@ class Loader():
             raise LoadError(LoadErrorReason.INVALID_DATA,
                             "{}: Expected junction but element kind is {}".format(filename, meta_element.kind))
 
-        platform = Platform.get_platform()
-        element = Element._new_from_meta(meta_element, platform.artifactcache)
+        element = Element._new_from_meta(meta_element, self._context.artifactcache)
         element._preflight()
 
         sources = list(element.sources())

buildstream/_platform/darwin.py

+#
+#  Copyright (C) 2017 Codethink Limited
+#  Copyright (C) 2018 Bloomberg Finance LP
+#
+#  This program is free software; you can redistribute it and/or
+#  modify it under the terms of the GNU Lesser General Public
+#  License as published by the Free Software Foundation; either
+#  version 2 of the License, or (at your option) any later version.
+#
+#  This library is distributed in the hope that it will be useful,
+#  but WITHOUT ANY WARRANTY; without even the implied warranty of
+#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.	 See the GNU
+#  Lesser General Public License for more details.
+#
+#  You should have received a copy of the GNU Lesser General Public
+#  License along with this library. If not, see <http://www.gnu.org/licenses/>.
+
+import os
+import resource
+
+from .._exceptions import PlatformError
+from ..sandbox import SandboxDummy
+
+from . import Platform
+
+
+class Darwin(Platform):
+
+    # This value comes from OPEN_MAX in syslimits.h
+    OPEN_MAX = 10240
+
+    def __init__(self, context):
+
+        super().__init__(context)
+
+    def create_sandbox(self, *args, **kwargs):
+        return SandboxDummy(*args, **kwargs)
+
+    def check_sandbox_config(self, config):
+        # Accept all sandbox configs as it's irrelevant with the dummy sandbox (no Sandbox.run).
+        return True
+
+    def get_cpu_count(self, cap=None):
+        if cap < os.cpu_count():
+            return cap
+        else:
+            return os.cpu_count()
+
+    def set_resource_limits(self, soft_limit=OPEN_MAX, hard_limit=None):
+        super().set_resource_limits(soft_limit)

buildstream/_platform/linux.py

@@ -17,42 +17,62 @@
 #  Authors:
 #        Tristan Maat <tristan.maat@codethink.co.uk>
 
+import os
 import subprocess
 
 from .. import _site
 from .. import utils
-from .._artifactcache.cascache import CASCache
 from .._message import Message, MessageType
-from ..sandbox import SandboxBwrap
+from ..sandbox import SandboxDummy
 
 from . import Platform
 
 
 class Linux(Platform):
 
-    def __init__(self, context):
+    def __init__(self):
 
-        super().__init__(context)
+        super().__init__()
+
+        self._uid = os.geteuid()
+        self._gid = os.getegid()
 
         self._die_with_parent_available = _site.check_bwrap_version(0, 1, 8)
-        self._user_ns_available = self._check_user_ns_available(context)
-        self._artifact_cache = CASCache(context, enable_push=self._user_ns_available)
 
-    @property
-    def artifactcache(self):
-        return self._artifact_cache
+        if self._local_sandbox_available():
+            self._user_ns_available = self._check_user_ns_available()
+        else:
+            self._user_ns_available = False
 
     def create_sandbox(self, *args, **kwargs):
-        # Inform the bubblewrap sandbox as to whether it can use user namespaces or not
-        kwargs['user_ns_available'] = self._user_ns_available
-        kwargs['die_with_parent_available'] = self._die_with_parent_available
-        return SandboxBwrap(*args, **kwargs)
+        if not self._local_sandbox_available():
+            return SandboxDummy(*args, **kwargs)
+        else:
+            from ..sandbox._sandboxbwrap import SandboxBwrap
+            # Inform the bubblewrap sandbox as to whether it can use user namespaces or not
+            kwargs['user_ns_available'] = self._user_ns_available
+            kwargs['die_with_parent_available'] = self._die_with_parent_available
+            return SandboxBwrap(*args, **kwargs)
+
+    def check_sandbox_config(self, config):
+        if self._user_ns_available:
+            # User namespace support allows arbitrary build UID/GID settings.
+            return True
+        else:
+            # Without user namespace support, the UID/GID in the sandbox
+            # will match the host UID/GID.
+            return config.build_uid == self._uid and config.build_gid == self._gid
 
     ################################################
     #              Private Methods                 #
     ################################################
-    def _check_user_ns_available(self, context):
+    def _local_sandbox_available(self):
+        try:
+            return os.path.exists(utils.get_host_tool('bwrap')) and os.path.exists('/dev/fuse')
+        except utils.ProgramNotFoundError:
+            return False
 
+    def _check_user_ns_available(self):
         # Here, lets check if bwrap is able to create user namespaces,
         # issue a warning if it's not available, and save the state
         # locally so that we can inform the sandbox to not try it
@@ -75,9 +95,4 @@ class Linux(Platform):
             return True
 
         else:
-            context.message(
-                Message(None, MessageType.WARN,
-                        "Unable to create user namespaces with bubblewrap, resorting to fallback",
-                        detail="Some builds may not function due to lack of uid / gid 0, " +
-                        "artifacts created will not be trusted for push purposes."))
             return False

buildstream/_platform/platform.py

@@ -19,6 +19,7 @@
 
 import os
 import sys
+import resource
 
 from .._exceptions import PlatformError, ImplError
 
@@ -29,50 +30,44 @@ class Platform():
     # Platform()
     #
     # A class to manage platform-specific details. Currently holds the
-    # sandbox factory, the artifact cache and staging operations, as
-    # well as platform helpers.
+    # sandbox factory as well as platform helpers.
     #
-    # Args:
-    #     context (context): The project context
-    #
-    def __init__(self, context):
-        self.context = context
+    def __init__(self):
+        self.set_resource_limits()
 
     @classmethod
-    def create_instance(cls, *args, **kwargs):
-        if sys.platform.startswith('linux'):
-            backend = 'linux'
-        else:
-            backend = 'unix'
-
+    def _create_instance(cls):
         # Meant for testing purposes and therefore hidden in the
         # deepest corners of the source code. Try not to abuse this,
         # please?
         if os.getenv('BST_FORCE_BACKEND'):
             backend = os.getenv('BST_FORCE_BACKEND')
+        elif sys.platform.startswith('linux'):
+            backend = 'linux'
+        elif sys.platform.startswith('darwin'):
+            backend = 'darwin'
+        else:
+            backend = 'unix'
 
         if backend == 'linux':
             from .linux import Linux as PlatformImpl
+        elif backend == 'darwin':
+            from .darwin import Darwin as PlatformImpl
         elif backend == 'unix':
             from .unix import Unix as PlatformImpl
         else:
             raise PlatformError("No such platform: '{}'".format(backend))
 
-        cls._instance = PlatformImpl(*args, **kwargs)
+        cls._instance = PlatformImpl()
 
     @classmethod
     def get_platform(cls):
         if not cls._instance:
-            raise PlatformError("Platform needs to be initialized first")
+            cls._create_instance()
         return cls._instance
 
-    ##################################################################
-    #                       Platform properties                      #
-    ##################################################################
-    @property
-    def artifactcache(self):
-        raise ImplError("Platform {platform} does not implement an artifactcache"
-                        .format(platform=type(self).__name__))
+    def get_cpu_count(self, cap=None):
+        return min(len(os.sched_getaffinity(0)), cap)
 
     ##################################################################
     #                        Sandbox functions                       #
@@ -92,3 +87,19 @@ class Platform():
     def create_sandbox(self, *args, **kwargs):
         raise ImplError("Platform {platform} does not implement create_sandbox()"
                         .format(platform=type(self).__name__))
+
+    def check_sandbox_config(self, config):
+        raise ImplError("Platform {platform} does not implement check_sandbox_config()"
+                        .format(platform=type(self).__name__))
+
+    def set_resource_limits(self, soft_limit=None, hard_limit=None):
+        # Need to set resources for _frontend/app.py as this is dependent on the platform
+        # SafeHardlinks FUSE needs to hold file descriptors for all processes in the sandbox.
+        # Avoid hitting the limit too quickly.
+        limits = resource.getrlimit(resource.RLIMIT_NOFILE)
+        if limits[0] != limits[1]:
+            if soft_limit is None:
+                soft_limit = limits[1]
+            if hard_limit is None:
+                hard_limit = limits[1]
+            resource.setrlimit(resource.RLIMIT_NOFILE, (soft_limit, hard_limit))

buildstream/_platform/unix.py

@@ -19,27 +19,29 @@
 
 import os
 
-from .._artifactcache.cascache import CASCache
 from .._exceptions import PlatformError
-from ..sandbox import SandboxChroot
 
 from . import Platform
 
 
 class Unix(Platform):
 
-    def __init__(self, context):
+    def __init__(self):
 
-        super().__init__(context)
-        self._artifact_cache = CASCache(context)
+        super().__init__()
+
+        self._uid = os.geteuid()
+        self._gid = os.getegid()
 
         # Not necessarily 100% reliable, but we want to fail early.
-        if os.geteuid() != 0:
+        if self._uid != 0:
             raise PlatformError("Root privileges are required to run without bubblewrap.")
 
-    @property
-    def artifactcache(self):
-        return self._artifact_cache
-
     def create_sandbox(self, *args, **kwargs):
+        from ..sandbox._sandboxchroot import SandboxChroot
         return SandboxChroot(*args, **kwargs)
+
+    def check_sandbox_config(self, config):
+        # With the chroot sandbox, the UID/GID in the sandbox
+        # will match the host UID/GID (typically 0/0).
+        return config.build_uid == self._uid and config.build_gid == self._gid

buildstream/_project.py

@@ -38,6 +38,7 @@ from ._loader import Loader
 from .element import Element
 from ._message import Message, MessageType
 from ._includes import Includes
+from ._platform import Platform
 
 
 # Project Configuration file
@@ -617,7 +618,8 @@ class Project():
         # Based on some testing (mainly on AWS), maximum effective
         # max-jobs value seems to be around 8-10 if we have enough cores
         # users should set values based on workload and build infrastructure
-        output.base_variables['max-jobs'] = str(min(len(os.sched_getaffinity(0)), 8))
+        platform = Platform.get_platform()
+        output.base_variables['max-jobs'] = str(platform.get_cpu_count(8))
 
         # Export options into variables, if that was requested
         output.options.export_variables(output.base_variables)

buildstream/_scheduler/jobs/cachesizejob.py

@@ -17,7 +17,6 @@
 #        Tristan Daniël Maat <tristan.maat@codethink.co.uk>
 #
 from .job import Job
-from ..._platform import Platform
 
 
 class CacheSizeJob(Job):
@@ -25,8 +24,8 @@ class CacheSizeJob(Job):
         super().__init__(*args, **kwargs)
         self._complete_cb = complete_cb
 
-        platform = Platform.get_platform()
-        self._artifacts = platform.artifactcache
+        context = self._scheduler.context
+        self._artifacts = context.artifactcache
 
     def child_process(self):
         return self._artifacts.compute_cache_size()

buildstream/_scheduler/jobs/cleanupjob.py

@@ -17,15 +17,14 @@
 #        Tristan Daniël Maat <tristan.maat@codethink.co.uk>
 #
 from .job import Job
-from ..._platform import Platform
 
 
 class CleanupJob(Job):
     def __init__(self, *args, **kwargs):
         super().__init__(*args, **kwargs)
 
-        platform = Platform.get_platform()
-        self._artifacts = platform.artifactcache
+        context = self._scheduler.context
+        self._artifacts = context.artifactcache
 
     def child_process(self):
         return self._artifacts.clean()

buildstream/_scheduler/queues/buildqueue.py

@@ -24,7 +24,6 @@ from . import Queue, QueueStatus
 from ..jobs import ElementJob
 from ..resources import ResourceType
 from ..._message import MessageType
-from ..._platform import Platform
 
 
 # A queue which assembles elements
@@ -94,8 +93,8 @@ class BuildQueue(Queue):
         # as returned from Element._assemble() to the estimated
         # artifact cache size
         #
-        platform = Platform.get_platform()
-        artifacts = platform.artifactcache
+        context = self._scheduler.context
+        artifacts = context.artifactcache
 
         artifacts.add_artifact_size(artifact_size)
 

buildstream/_scheduler/scheduler.py

@@ -29,7 +29,6 @@ from contextlib import contextmanager
 # Local imports
 from .resources import Resources, ResourceType
 from .jobs import CacheSizeJob, CleanupJob
-from .._platform import Platform
 
 
 # A decent return code for Scheduler.run()
@@ -348,8 +347,8 @@ class Scheduler():
     #       which will report the calculated cache size.
     #
     def _run_cleanup(self, cache_size):
-        platform = Platform.get_platform()
-        artifacts = platform.artifactcache
+        context = self.context
+        artifacts = context.artifactcache
 
         if not artifacts.has_quota_exceeded():
             return

buildstream/_stream.py

@@ -32,7 +32,6 @@ from ._exceptions import StreamError, ImplError, BstError, set_last_task_error
 from ._message import Message, MessageType
 from ._scheduler import Scheduler, SchedStatus, TrackQueue, FetchQueue, BuildQueue, PullQueue, PushQueue
 from ._pipeline import Pipeline, PipelineSelection
-from ._platform import Platform
 from . import utils, _yaml, _site
 from . import Scope, Consistency
 
@@ -71,8 +70,7 @@ class Stream():
         #
         # Private members
         #
-        self._platform = Platform.get_platform()
-        self._artifacts = self._platform.artifactcache
+        self._artifacts = context.artifactcache
         self._context = context
         self._project = project
         self._pipeline = Pipeline(context, project, self._artifacts)

buildstream/element.py

@@ -246,15 +246,23 @@ class Element(Plugin):
         self.__config = self.__extract_config(meta)
         self._configure(self.__config)
 
-        # Extract Sandbox config
-        self.__sandbox_config = self.__extract_sandbox_config(meta)
-
         # Extract remote execution URL
         if not self.__is_junction:
             self.__remote_execution_url = project.remote_execution_url
         else:
             self.__remote_execution_url = None
 
+        # Extract Sandbox config
+        self.__sandbox_config = self.__extract_sandbox_config(meta)
+
+        self.__sandbox_config_supported = True
+        if not self.__use_remote_execution():
+            platform = Platform.get_platform()
+            if not platform.check_sandbox_config(self.__sandbox_config):
+                # Local sandbox does not fully support specified sandbox config.
+                # This will taint the artifact, disable pushing.
+                self.__sandbox_config_supported = False
+
     def __lt__(self, other):
         return self.name < other.name
 
@@ -1521,6 +1529,11 @@ class Element(Plugin):
         context = self._get_context()
         with self._output_file() as output_file:
 
+            if not self.__sandbox_config_supported:
+                self.warn("Sandbox configuration is not supported by the platform.",
+                          detail="Falling back to UID {} GID {}. Artifact will not be pushed."
+                          .format(self.__sandbox_config.build_uid, self.__sandbox_config.build_gid))
+
             # Explicitly clean it up, keep the build dir around if exceptions are raised
             os.makedirs(context.builddir, exist_ok=True)
             rootdir = tempfile.mkdtemp(prefix="{}-".format(self.normal_name), dir=context.builddir)
@@ -2110,10 +2123,19 @@ class Element(Plugin):
             workspaced_dependencies = self.__get_artifact_metadata_workspaced_dependencies()
 
             # Other conditions should be or-ed
-            self.__tainted = workspaced or workspaced_dependencies
+            self.__tainted = (workspaced or workspaced_dependencies or
+                              not self.__sandbox_config_supported)
 
         return self.__tainted
 
+    # __use_remote_execution():
+    #
+    # Returns True if remote execution is configured and the element plugin
+    # supports it.
+    #
+    def __use_remote_execution(self):
+        return self.__remote_execution_url and self.BST_VIRTUAL_DIRECTORY
+
     # __sandbox():
     #
     # A context manager to prepare a Sandbox object at the specified directory,
@@ -2135,9 +2157,7 @@ class Element(Plugin):
         project = self._get_project()
         platform = Platform.get_platform()
 
-        if (directory is not None and
-            self.__remote_execution_url and
-            self.BST_VIRTUAL_DIRECTORY):
+        if directory is not None and self.__use_remote_execution():
 
             self.info("Using a remote sandbox for artifact {} with directory '{}'".format(self.name, directory))
 

buildstream/sandbox/__init__.py

@@ -18,6 +18,5 @@
 #        Tristan Maat <tristan.maat@codethink.co.uk>
 
 from .sandbox import Sandbox, SandboxFlags
-from ._sandboxchroot import SandboxChroot
-from ._sandboxbwrap import SandboxBwrap
 from ._sandboxremote import SandboxRemote
+from ._sandboxdummy import SandboxDummy

buildstream/sandbox/_sandboxdummy.py

+#
+#  Copyright (C) 2017 Codethink Limited
+#
+#  This program is free software; you can redistribute it and/or
+#  modify it under the terms of the GNU Lesser General Public
+#  License as published by the Free Software Foundation; either
+#  version 2 of the License, or (at your option) any later version.
+#
+#  This library is distributed in the hope that it will be useful,
+#  but WITHOUT ANY WARRANTY; without even the implied warranty of
+#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.	 See the GNU
+#  Lesser General Public License for more details.
+#
+#  You should have received a copy of the GNU Lesser General Public
+#  License along with this library. If not, see <http://www.gnu.org/licenses/>.
+#
+#  Authors:
+
+from .._exceptions import SandboxError
+from . import Sandbox
+
+
+class SandboxDummy(Sandbox):
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+
+    def run(self, command, flags, *, cwd=None, env=None):
+
+        # Fallback to the sandbox default settings for
+        # the cwd and env.
+        #
+        cwd = self._get_work_directory(cwd=cwd)
+        env = self._get_environment(cwd=cwd, env=env)
+
+        if not self._has_command(command[0], env):
+            raise SandboxError("Staged artifacts do not provide command "
+                               "'{}'".format(command[0]),
+                               reason='missing-command')
+
+        raise SandboxError("This platform does not support local builds")

buildstream/sandbox/_sandboxremote.py

@@ -27,7 +27,6 @@ from . import Sandbox
 from ..storage._filebaseddirectory import FileBasedDirectory
 from ..storage._casbaseddirectory import CasBasedDirectory
 from .._protos.build.bazel.remote.execution.v2 import remote_execution_pb2, remote_execution_pb2_grpc
-from .._platform import Platform
 
 
 class SandboxError(Exception):
@@ -71,8 +70,8 @@ class SandboxRemote(Sandbox):
                                                       output_files=[],
                                                       output_directories=[self._output_directory],
                                                       platform=None)
-        platform = Platform.get_platform()
-        cascache = platform.artifactcache
+        context = self._get_context()
+        cascache = context.artifactcache
         # Upload the Command message to the remote CAS server
         command_digest = cascache.push_message(self._get_project(), remote_command)
         if not command_digest or not cascache.verify_digest_pushed(self._get_project(), command_digest):
@@ -134,8 +133,8 @@ class SandboxRemote(Sandbox):
         if tree_digest is None or not tree_digest.hash:
             raise SandboxError("Output directory structure had no digest attached.")
 
-        platform = Platform.get_platform()
-        cascache = platform.artifactcache
+        context = self._get_context()
+        cascache = context.artifactcache
         # Now do a pull to ensure we have the necessary parts.
         dir_digest = cascache.pull_tree(self._get_project(), tree_digest)
         if dir_digest is None or not dir_digest.hash or not dir_digest.size_bytes:
@@ -170,8 +169,8 @@ class SandboxRemote(Sandbox):
 
         upload_vdir.recalculate_hash()
 
-        platform = Platform.get_platform()
-        cascache = platform.artifactcache
+        context = self._get_context()
+        cascache = context.artifactcache
         # Now, push that key (without necessarily needing a ref) to the remote.
         cascache.push_directory(self._get_project(), upload_vdir)
         if not cascache.verify_digest_pushed(self._get_project(), upload_vdir.ref):

buildstream/storage/_casbaseddirectory.py

@@ -38,7 +38,6 @@ from .._exceptions import BstError
 from .directory import Directory, VirtualDirectoryError
 from ._filebaseddirectory import FileBasedDirectory
 from ..utils import FileListResult, safe_copy, list_relative_paths
-from .._artifactcache.cascache import CASCache
 
 
 class IndexEntry():
@@ -80,7 +79,7 @@ class CasBasedDirectory(Directory):
         self.filename = filename
         self.common_name = common_name
         self.pb2_directory = remote_execution_pb2.Directory()
-        self.cas_cache = CASCache(context)
+        self.cas_cache = context.artifactcache
         if ref:
             with open(self.cas_cache.objpath(ref), 'rb') as f:
                 self.pb2_directory.ParseFromString(f.read())