Per-BlenderID-user cache.

Different users might have different access rights, and thus access
to different information.

blender_cloud/cache.py

@@ -0,0 +1,63 @@
+"""HTTP Cache management.
+
+This module configures a cached session for the Requests package.
+It allows for filesystem-based caching of HTTP requests.
+
+Requires the 3rd party packages CacheControl and lockfile.
+"""
+
+import os
+import logging
+import requests
+import cachecontrol
+from cachecontrol.caches import FileCache
+
+from . import appdirs
+
+log = logging.getLogger(__name__)
+_session = None  # requests.Session object that's set up for caching by requests_session().
+
+
+def cache_directory(*subdirs) -> str:
+    """Returns an OS-specifc cache location, and ensures it exists.
+
+    Should be replaced with a call to bpy.utils.user_resource('CACHE', ...)
+    once https://developer.blender.org/T47684 is finished.
+
+    :param subdirs: extra subdirectories inside the cache directory.
+
+    >>> cache_directory()
+    '.../blender_cloud/your_username'
+    >>> cache_directory('sub1', 'sub2')
+    '.../blender_cloud/your_username/sub1/sub2'
+    """
+
+    from . import pillar
+
+    profile = pillar.blender_id_profile() or {'username': 'anonymous'}
+
+    # TODO: use bpy.utils.user_resource('CACHE', ...)
+    # once https://developer.blender.org/T47684 is finished.
+    user_cache_dir = appdirs.user_cache_dir(appname='Blender', appauthor=False)
+    cache_dir = os.path.join(user_cache_dir, 'blender_cloud', profile['username'], *subdirs)
+
+    os.makedirs(cache_dir, mode=0o700, exist_ok=True)
+
+    return cache_dir
+
+
+def requests_session() -> requests.Session:
+    """Creates a Requests-Cache session object."""
+
+    global _session
+
+    if _session is not None:
+        return _session
+
+    cache_name = cache_directory('blender_cloud_http')
+    log.info('Storing cache in %s' % cache_name)
+
+    _session = cachecontrol.CacheControl(sess=requests.session(),
+                                         cache=FileCache(cache_name))
+
+    return _session