Merge pull request #1638 from matrix-org/kegan/sync-event-fields

Implement "event_fields" in filters

3 files changed, 127 insertions, 14 deletions

diff --git a/synapse/api/filtering.py b/synapse/api/filtering.py
index 3b3ef70750..6f16e4d406 100644
--- a/synapse/api/filtering.py
+++ b/synapse/api/filtering.py
@@ -71,6 +71,21 @@ class Filtering(object):
                 if key in user_filter_json["room"]:
                     self._check_definition(user_filter_json["room"][key])
 
+        if "event_fields" in user_filter_json:
+            if type(user_filter_json["event_fields"]) != list:
+                raise SynapseError(400, "event_fields must be a list of strings")
+            for field in user_filter_json["event_fields"]:
+                if not isinstance(field, basestring):
+                    raise SynapseError(400, "Event field must be a string")
+                # Don't allow '\\' in event field filters. This makes matching
+                # events a lot easier as we can then use a negative lookbehind
+                # assertion to split '\.' If we allowed \\ then it would
+                # incorrectly split '\\.' See synapse.events.utils.serialize_event
+                if r'\\' in field:
+                    raise SynapseError(
+                        400, r'The escape character \ cannot itself be escaped'
+                    )
+
     def _check_definition_room_lists(self, definition):
         """Check that "rooms" and "not_rooms" are lists of room ids if they
         are present
@@ -152,6 +167,7 @@ class FilterCollection(object):
         self.include_leave = filter_json.get("room", {}).get(
             "include_leave", False
         )
+        self.event_fields = filter_json.get("event_fields", [])
 
     def __repr__(self):
         return "<FilterCollection %s>" % (json.dumps(self._filter_json),)
diff --git a/synapse/events/utils.py b/synapse/events/utils.py
index 0e9fd902af..5bbaef8187 100644
--- a/synapse/events/utils.py
+++ b/synapse/events/utils.py
@@ -16,6 +16,17 @@
 from synapse.api.constants import EventTypes
 from . import EventBase
 
+from frozendict import frozendict
+
+import re
+
+# Split strings on "." but not "\." This uses a negative lookbehind assertion for '\'
+# (?<!stuff) matches if the current position in the string is not preceded
+# by a match for 'stuff'.
+# TODO: This is fast, but fails to handle "foo\\.bar" which should be treated as
+#       the literal fields "foo\" and "bar" but will instead be treated as "foo\\.bar"
+SPLIT_FIELD_REGEX = re.compile(r'(?<!\\)\.')
+
 
 def prune_event(event):
     """ Returns a pruned version of the given event, which removes all keys we
@@ -97,6 +108,83 @@ def prune_event(event):
     )
 
 
+def _copy_field(src, dst, field):
+    """Copy the field in 'src' to 'dst'.
+
+    For example, if src={"foo":{"bar":5}} and dst={}, and field=["foo","bar"]
+    then dst={"foo":{"bar":5}}.
+
+    Args:
+        src(dict): The dict to read from.
+        dst(dict): The dict to modify.
+        field(list<str>): List of keys to drill down to in 'src'.
+    """
+    if len(field) == 0:  # this should be impossible
+        return
+    if len(field) == 1:  # common case e.g. 'origin_server_ts'
+        if field[0] in src:
+            dst[field[0]] = src[field[0]]
+        return
+
+    # Else is a nested field e.g. 'content.body'
+    # Pop the last field as that's the key to move across and we need the
+    # parent dict in order to access the data. Drill down to the right dict.
+    key_to_move = field.pop(-1)
+    sub_dict = src
+    for sub_field in field:  # e.g. sub_field => "content"
+        if sub_field in sub_dict and type(sub_dict[sub_field]) in [dict, frozendict]:
+            sub_dict = sub_dict[sub_field]
+        else:
+            return
+
+    if key_to_move not in sub_dict:
+        return
+
+    # Insert the key into the output dictionary, creating nested objects
+    # as required. We couldn't do this any earlier or else we'd need to delete
+    # the empty objects if the key didn't exist.
+    sub_out_dict = dst
+    for sub_field in field:
+        sub_out_dict = sub_out_dict.setdefault(sub_field, {})
+    sub_out_dict[key_to_move] = sub_dict[key_to_move]
+
+
+def only_fields(dictionary, fields):
+    """Return a new dict with only the fields in 'dictionary' which are present
+    in 'fields'.
+
+    If there are no event fields specified then all fields are included.
+    The entries may include '.' charaters to indicate sub-fields.
+    So ['content.body'] will include the 'body' field of the 'content' object.
+    A literal '.' character in a field name may be escaped using a '\'.
+
+    Args:
+        dictionary(dict): The dictionary to read from.
+        fields(list<str>): A list of fields to copy over. Only shallow refs are
+        taken.
+    Returns:
+        dict: A new dictionary with only the given fields. If fields was empty,
+        the same dictionary is returned.
+    """
+    if len(fields) == 0:
+        return dictionary
+
+    # for each field, convert it:
+    # ["content.body.thing\.with\.dots"] => [["content", "body", "thing\.with\.dots"]]
+    split_fields = [SPLIT_FIELD_REGEX.split(f) for f in fields]
+
+    # for each element of the output array of arrays:
+    # remove escaping so we can use the right key names.
+    split_fields[:] = [
+        [f.replace(r'\.', r'.') for f in field_array] for field_array in split_fields
+    ]
+
+    output = {}
+    for field_array in split_fields:
+        _copy_field(dictionary, output, field_array)
+    return output
+
+
 def format_event_raw(d):
     return d
 
@@ -137,7 +225,7 @@ def format_event_for_client_v2_without_room_id(d):
 
 def serialize_event(e, time_now_ms, as_client_event=True,
                     event_format=format_event_for_client_v1,
-                    token_id=None):
+                    token_id=None, only_event_fields=None):
     # FIXME(erikj): To handle the case of presence events and the like
     if not isinstance(e, EventBase):
         return e
@@ -164,6 +252,12 @@ def serialize_event(e, time_now_ms, as_client_event=True,
                 d["unsigned"]["transaction_id"] = txn_id
 
     if as_client_event:
-        return event_format(d)
-    else:
-        return d
+        d = event_format(d)
+
+    if only_event_fields:
+        if (not isinstance(only_event_fields, list) or
+                not all(isinstance(f, basestring) for f in only_event_fields)):
+            raise TypeError("only_event_fields must be a list of strings")
+        d = only_fields(d, only_event_fields)
+
+    return d
diff --git a/synapse/rest/client/v2_alpha/sync.py b/synapse/rest/client/v2_alpha/sync.py
index 6fc63715aa..7199ec883a 100644
--- a/synapse/rest/client/v2_alpha/sync.py
+++ b/synapse/rest/client/v2_alpha/sync.py
@@ -162,7 +162,7 @@ class SyncRestServlet(RestServlet):
         time_now = self.clock.time_msec()
 
         joined = self.encode_joined(
-            sync_result.joined, time_now, requester.access_token_id
+            sync_result.joined, time_now, requester.access_token_id, filter.event_fields
         )
 
         invited = self.encode_invited(
@@ -170,7 +170,7 @@ class SyncRestServlet(RestServlet):
         )
 
         archived = self.encode_archived(
-            sync_result.archived, time_now, requester.access_token_id
+            sync_result.archived, time_now, requester.access_token_id, filter.event_fields
         )
 
         response_content = {
@@ -197,7 +197,7 @@ class SyncRestServlet(RestServlet):
             formatted.append(event)
         return {"events": formatted}
 
-    def encode_joined(self, rooms, time_now, token_id):
+    def encode_joined(self, rooms, time_now, token_id, event_fields):
         """
         Encode the joined rooms in a sync result
 
@@ -208,7 +208,8 @@ class SyncRestServlet(RestServlet):
                 calculations
             token_id(int): ID of the user's auth token - used for namespacing
                 of transaction IDs
-
+            event_fields(list<str>): List of event fields to include. If empty,
+            all fields will be returned.
         Returns:
             dict[str, dict[str, object]]: the joined rooms list, in our
                 response format
@@ -216,7 +217,7 @@ class SyncRestServlet(RestServlet):
         joined = {}
         for room in rooms:
             joined[room.room_id] = self.encode_room(
-                room, time_now, token_id
+                room, time_now, token_id, only_fields=event_fields
             )
 
         return joined
@@ -253,7 +254,7 @@ class SyncRestServlet(RestServlet):
 
         return invited
 
-    def encode_archived(self, rooms, time_now, token_id):
+    def encode_archived(self, rooms, time_now, token_id, event_fields):
         """
         Encode the archived rooms in a sync result
 
@@ -264,7 +265,8 @@ class SyncRestServlet(RestServlet):
                 calculations
             token_id(int): ID of the user's auth token - used for namespacing
                 of transaction IDs
-
+            event_fields(list<str>): List of event fields to include. If empty,
+            all fields will be returned.
         Returns:
             dict[str, dict[str, object]]: The invited rooms list, in our
                 response format
@@ -272,13 +274,13 @@ class SyncRestServlet(RestServlet):
         joined = {}
         for room in rooms:
             joined[room.room_id] = self.encode_room(
-                room, time_now, token_id, joined=False
+                room, time_now, token_id, joined=False, only_fields=event_fields
             )
 
         return joined
 
     @staticmethod
-    def encode_room(room, time_now, token_id, joined=True):
+    def encode_room(room, time_now, token_id, joined=True, only_fields=None):
         """
         Args:
             room (JoinedSyncResult|ArchivedSyncResult): sync result for a
@@ -289,7 +291,7 @@ class SyncRestServlet(RestServlet):
                 of transaction IDs
             joined (bool): True if the user is joined to this room - will mean
                 we handle ephemeral events
-
+            only_fields(list<str>): Optional. The list of event fields to include.
         Returns:
             dict[str, object]: the room, encoded in our response format
         """
@@ -298,6 +300,7 @@ class SyncRestServlet(RestServlet):
             return serialize_event(
                 event, time_now, token_id=token_id,
                 event_format=format_event_for_client_v2_without_room_id,
+                only_event_fields=only_fields,
             )
 
         state_dict = room.state