--- a/src/memory/cache.py	Fri Mar 02 17:37:41 2018 +0100
+++ b/src/memory/cache.py	Fri Mar 02 17:40:09 2018 +0100
@@ -27,16 +27,25 @@
 import os.path
 import time
 
+DEFAULT_EXT = '.raw'
+
 
 class Cache(object):
     """generic file caching"""
 
-    def __init__(self, host, profile=None):
+    def __init__(self, host, profile):
+        """
+        @param profile(unicode, None): ame of the profile to set the cache for
+            if None, the cache will be common for all profiles
+        """
         self.profile = profile
-        self.cache_dir = os.path.join(
-            host.memory.getConfig('', 'local_dir'),
-            C.CACHE_DIR,
-            regex.pathEscape(profile or ''))
+        path_elts = [host.memory.getConfig('', 'local_dir'), C.CACHE_DIR]
+        if profile:
+            path_elts.extend([u'profiles',regex.pathEscape(profile)])
+        else:
+            path_elts.append(u'common')
+        self.cache_dir = os.path.join(*path_elts)
+
         if not os.path.exists(self.cache_dir):
             os.makedirs(self.cache_dir)
 
@@ -59,7 +68,7 @@
         """
         uid = uid.strip()
         if not uid:
-            return None
+            raise exceptions.InternalError(u"uid must not be empty")
         cache_url = self.getPath(uid)
         if not os.path.exists(cache_url):
             return None
@@ -86,7 +95,7 @@
 
         return self.getPath(cache_data['filename'])
 
-    def cacheData(self, source, uid, mime_type=u'', max_age=None, filename=None):
+    def cacheData(self, source, uid, mime_type=None, max_age=None, filename=None):
         """create cache metadata and file object to use for actual data
 
         @param source(unicode): source of the cache (should be plugin's import_name)
@@ -102,21 +111,25 @@
         @return(file): file object opened in write mode
             you have to close it yourself (hint: use with statement)
         """
-        # FIXME: is it needed to use a separate thread?
-        #        probably not with the little data expected with BoB
         cache_url = self.getPath(uid)
-        ext = mimetypes.guess_extension(mime_type, strict=False)
-        if ext is None:
-            log.warning(u"can't find extension for MIME type {}".format(mime_type))
-            ext = '.dump'
         if filename is None:
+            if mime_type:
+                ext = mimetypes.guess_extension(mime_type, strict=False)
+                if ext is None:
+                    log.warning(u"can't find extension for MIME type {}".format(mime_type))
+                    ext = DEFAULT_EXT
+                elif ext == u'.jpe':
+                    ext = u'.jpg'
+            else:
+                ext = DEFAULT_EXT
+                mime_type = None
             filename = uid + ext
         if max_age is None:
             max_age = C.DEFAULT_MAX_AGE
-        cache_data = {'source': source,
-                      'filename': filename,
-                      'eol': int(time.time()) + max_age,
-                      'mime_type': mime_type,
+        cache_data = {u'source': source,
+                      u'filename': filename,
+                      u'eol': int(time.time()) + max_age,
+                      u'mime_type': mime_type,
                       }
         file_path = self.getPath(filename)