Cache helper added

The cache helper is a simple helper to cache data
in Redis back-end. The format in the cache is the following:
m:<module name>:sha1(key) -> value. Default expiration is 86400 seconds.

helpers/cache.py

@@ -1,13 +1,79 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+#
+# MISP modules helper - cache
+#
+# Copyright (C) 2016 Alexandre Dulaunoy
+# Copyright (C) 2016 CIRCL - Computer Incident Response Center Luxembourg
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero 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 Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
 import redis
+import hashlib
 
 port = 6379
 hostname = '127.0.0.1'
+db = 5
+
 
 def selftest(enable=True):
     if not enable:
         return False
-    r = redis.StrictRedis(host='localhost', port=port)
+    r = redis.StrictRedis(host=hostname, port=port, db=db)
     try:
-        r.set('test','selftest')
+        r.set('test', 'selftest')
     except:
         return 'Redis not running or not installed. Helper will be disabled.'
+
+
+def get(modulename=None, query=None, value=None, debug=False):
+    if (modulename is None or query is None or value is None):
+        return False
+    r = redis.StrictRedis(host=hostname, port=port, db=db)
+    h = hashlib.sha1()
+    h.update(query.encode('UTF-8'))
+    hv = h.hexdigest()
+    key = "m:"+modulename+":"+hv
+
+    if not r.exists(key):
+        if debug:
+            print ("Key {} added in cache".format(key))
+        r.set(key, value)
+        r.expire(key, 86400)
+    else:
+        if debug:
+            print ("Cache hit with Key {}".format(key))
+
+    return r.get(key)
+
+
+def flush():
+    r = redis.StrictRedis(host=hostname, port=port, db=db)
+    returncode = r.flushdb()
+    return returncode
+
+if __name__ == "__main__":
+    import sys
+    if selftest() is not None:
+        sys.exit()
+    else:
+        print ("Selftest ok")
+    v = get(modulename="testmodule", query="abcdef", value="barfoo", debug=True)
+    if v == b'barfoo':
+        print ("Cache ok")
+    v = get(modulename="testmodule")
+    if (not v):
+        print ("Failed ok")
+    if flush():
+        print ("Cache flushed ok")