add dbwrapper

1 files changed, 183 insertions, 0 deletions

diff --git a/soledad/src/leap/soledad/dbwrapper.py b/soledad/src/leap/soledad/dbwrapper.py
new file mode 100644
index 00000000..c16c4925
--- /dev/null
+++ b/soledad/src/leap/soledad/dbwrapper.py
@@ -0,0 +1,183 @@
+# -*- coding: utf-8 -*-
+# dbwrapper.py
+# Copyright (C) 2013 LEAP
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program 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 General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+"""
+Thread-safe wrapper for sqlite/pysqlcipher.
+
+*TODO*
+At some point we surely will want to switch to a twisted way of dealing
+with this, using defers and proper callbacks. But I had this tested for
+some time so postponing that refactor.
+"""
+import logging
+import threading
+import Queue
+import time
+
+import exceptions
+
+from functools import partial
+
+from leap.soledad import sqlcipher
+
+logger = logging.getLogger(__name__)
+
+
+class SQLCipherWrapper(threading.Thread):
+
+    def __init__(self, *args, **kwargs):
+        """
+        Initializes a wrapper that proxies method and attribute
+        access to an underlying SQLCipher instance. We instantiate sqlcipher
+        in a thread, and all method accesses communicate with it using a
+        Queue.
+
+        :param *args: position arguments to pass to pysqlcipher initialization
+        :type args: tuple
+
+        :param **kwargs: keyword arguments to pass to pysqlcipher
+                         initialization
+        :type kwargs: dict
+        """
+        threading.Thread.__init__(self)
+        self._db = None
+        self._wrargs = args, kwargs
+
+        self._queue = Queue.Queue()
+        self._stopped = threading.Event()
+
+        self.start()
+
+    def _init_db(self):
+        """
+        Initializes sqlcipher database.
+
+        This is called on a separate thread.
+        """
+        # instantiate u1db
+        args, kwargs = self._wrargs
+        self._db = sqlcipher.open(*args, **kwargs)
+
+    def run(self):
+        """
+        Main loop for the sqlcipher thread.
+        """
+        logger.debug("SQLCipherWrapper thread started.")
+        logger.debug("Initializing sqlcipher")
+        end_mths = ("__end_thread", "_SQLCipherWrapper__end_thread")
+
+        self._init_db()
+        self._lock = threading.Lock()
+
+        ct = 0
+        started = False
+
+        while True:
+            if self._db is None:
+                if started:
+                    break
+                if ct > 10:
+                    break  # XXX DEBUG
+                logger.debug('db not ready yet, waiting...')
+                time.sleep(1)
+                ct += 1
+
+            started = True
+
+            with self._lock:
+                try:
+                    mth, q, wrargs = self._queue.get()
+                except:
+                    logger.error("exception getting args from queue")
+
+                res = None
+                attr = getattr(self._db, mth, None)
+                if not attr:
+                    if mth not in end_mths:
+                        logger.error('method %s does not exist' % (mth,))
+                        res = AttributeError(
+                            "_db instance has no attribute %s" % mth)
+
+                elif callable(attr):
+                    # invoke the method with the passed args
+                    args = wrargs.get('args', [])
+                    kwargs = wrargs.get('kwargs', {})
+                    try:
+                        res = attr(*args, **kwargs)
+                    except Exception as e:
+                        logger.error(
+                            "Error on proxied method %s: '%r'." % (
+                            attr, e))
+                        res = e
+                else:
+                    # non-callable attribute
+                    res = attr
+                logger.debug('returning proxied db call...')
+                q.put(res)
+
+            if mth in end_mths:
+                logger.debug('ending thread')
+                break
+
+        logger.debug("SQLCipherWrapper thread terminated.")
+        self._stopped.set()
+
+    def close(self):
+        """
+        Closes the sqlcipher database and finishes the thread. This method
+        should always be called explicitely.
+        """
+        self.__getattr__('close')()
+        self.__end_thread()
+
+    def __getattr__(self, attr):
+        """
+        Returns _db proxied attributes.
+        """
+
+        def __proxied_mth(method, *args, **kwargs):
+            if not self._stopped.isSet():
+                wrargs = {'args': args, 'kwargs': kwargs}
+                q = Queue.Queue()
+                self._queue.put((method, q, wrargs))
+                res = q.get()
+                q.task_done()
+
+                if isinstance(res, exceptions.BaseException):
+                    # XXX should get the original bt
+                    raise res
+                return res
+            else:
+                logger.warning("tried to call proxied meth "
+                               "but stopped is set: %s" %
+                               (method,))
+
+        rgetattr = object.__getattribute__
+
+        if attr != "_db":
+            proxied = partial(__proxied_mth, attr)
+            return proxied
+
+        # fallback to regular behavior
+        return rgetattr(self, attr)
+
+    def __del__(self):
+        """
+        Do not trust this get called. No guarantees given. Because of a funny
+        dance with the refs and the way the gc works, we should be calling the
+        close method explicitely.
+        """
+        self.close()