Transfers: implement source selection strategies

Try to be more generic in the source filtering and selection code.
Introduce a SourceRankingStrategy class, which has an `apply` method
to actually apply the strategy to a source and decide what to do with
a source. Some strategies are filter-only: i.e. they only decide if
a source has to be ignored or not. Others are also ranking strategies:
they can return an integer which defines the cost of the source
according to this strategy. The order of ranking strategies is
important: it defines the order in which the costs will be compared to
sort the sources.

This change will definitely introduce some computational and memory
overhead, but I hope it will be low. Instead of hard-coded `filter()`
calls which are done once per request, now we have multiple object
traversals and function calls for each source of each request.

lib/rucio/core/request.py

@@ -56,8 +56,8 @@
 
 
 class RequestSource:
-    def __init__(self, rse_data, ranking=None, distance=None, file_path=None, scheme=None, url=None):
-        self.rse = rse_data
+    def __init__(self, rse: RseData, ranking=None, distance=None, file_path=None, scheme=None, url=None):
+        self.rse = rse
         self.distance = distance if distance is not None else 9999
         self.ranking = ranking if ranking is not None else 0
         self.file_path = file_path
@@ -82,7 +82,7 @@ def __init__(
             activity: str,
             attributes: Optional[Union[str, dict[str, Any]]],
             previous_attempt_id: Optional[str],
-            dest_rse_data: RseData,
+            dest_rse: RseData,
             account: InternalAccount,
             retry_count: int,
             priority: int,
@@ -102,7 +102,7 @@ def __init__(
         self._dict_attributes = None
         self._db_attributes = attributes
         self.previous_attempt_id = previous_attempt_id
-        self.dest_rse = dest_rse_data
+        self.dest_rse = dest_rse
         self.account = account
         self.retry_count = retry_count or 0
         self.priority = priority if priority is not None else 3
@@ -118,11 +118,15 @@ def __str__(self):
     @property
     def attributes(self):
         if self._dict_attributes is None:
-            self.attributes = self._db_attributes
+            self._dict_attributes = self._parse_db_attributes(self._db_attributes)
         return self._dict_attributes
 
     @attributes.setter
     def attributes(self, db_attributes):
+        self._dict_attributes = self._parse_db_attributes(db_attributes)
+
+    @staticmethod
+    def _parse_db_attributes(db_attributes):
         attr = {}
         if db_attributes:
             if isinstance(db_attributes, dict):
@@ -134,7 +138,7 @@ def attributes(self, db_attributes):
             attr['allow_tape_source'] = attr["allow_tape_source"] if (attr and "allow_tape_source" in attr) else True
             attr['dsn'] = attr["ds_name"] if (attr and "ds_name" in attr) else None
             attr['lifetime'] = attr.get('lifetime', -1)
-        self._dict_attributes = attr
+        return attr
 
 
 def should_retry_request(req, retry_protocol_mismatches):
@@ -546,19 +550,19 @@ def list_and_mark_transfer_requests_and_source_replicas(
         if not request:
             request = RequestWithSources(id_=request_id, request_type=req_type, rule_id=rule_id, scope=scope, name=name,
                                          md5=md5, adler32=adler32, byte_count=byte_count, activity=activity, attributes=attributes,
-                                         previous_attempt_id=previous_attempt_id, dest_rse_data=rse_collection[dest_rse_id],
+                                         previous_attempt_id=previous_attempt_id, dest_rse=rse_collection[dest_rse_id],
                                          account=account, retry_count=retry_count, priority=priority, transfertool=transfertool,
                                          requested_at=requested_at)
             requests_by_id[request_id] = request
             # if STAGEIN and destination RSE is QoS make sure the source is included
             if request.request_type == RequestType.STAGEIN and get_rse_attribute(rse_id=dest_rse_id, key='staging_required', session=session):
-                source = RequestSource(rse_data=rse_collection[dest_rse_id])
+                source = RequestSource(rse=rse_collection[dest_rse_id])
                 request.sources.append(source)
 
         if replica_rse_id is not None:
             replica_rse = rse_collection[replica_rse_id]
             replica_rse.name = replica_rse_name
-            source = RequestSource(rse_data=replica_rse, file_path=file_path,
+            source = RequestSource(rse=replica_rse, file_path=file_path,
                                    ranking=source_ranking, distance=distance, url=source_url)
             request.sources.append(source)
             if source_rse_id == replica_rse_id: