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-rw-r--r--.gitignore2
-rw-r--r--docs/admin_api/media_admin_api.md23
-rw-r--r--synapse/handlers/federation.py11
-rw-r--r--synapse/rest/client/v1/admin.py22
-rw-r--r--synapse/rest/media/v1/media_repository.py20
-rw-r--r--synapse/rest/media/v1/media_storage.py36
-rw-r--r--synapse/rest/media/v1/preview_url_resource.py55
-rw-r--r--synapse/rest/media/v1/thumbnail_resource.py3
-rw-r--r--synapse/server.py6
-rw-r--r--synapse/server.pyi3
-rw-r--r--synapse/state.py197
-rw-r--r--synapse/storage/events.py57
-rw-r--r--synapse/storage/room.py153
-rw-r--r--tests/rest/media/__init__.py14
-rw-r--r--tests/rest/media/v1/__init__.py14
-rw-r--r--tests/rest/media/v1/test_media_storage.py86
-rw-r--r--tests/test_state.py4
17 files changed, 525 insertions, 181 deletions
diff --git a/.gitignore b/.gitignore
index 491047c352..c8901eb206 100644
--- a/.gitignore
+++ b/.gitignore
@@ -46,3 +46,5 @@ static/client/register/register_config.js
 
 env/
 *.config
+
+.vscode/
diff --git a/docs/admin_api/media_admin_api.md b/docs/admin_api/media_admin_api.md
new file mode 100644
index 0000000000..abdbc1ea86
--- /dev/null
+++ b/docs/admin_api/media_admin_api.md
@@ -0,0 +1,23 @@
+# List all media in a room
+
+This API gets a list of known media in a room.
+
+The API is:
+```
+GET /_matrix/client/r0/admin/room/<room_id>/media
+```
+including an `access_token` of a server admin.
+
+It returns a JSON body like the following:
+```
+{
+    "local": [
+        "mxc://localhost/xwvutsrqponmlkjihgfedcba",
+        "mxc://localhost/abcdefghijklmnopqrstuvwx"
+    ],
+    "remote": [
+        "mxc://matrix.org/xwvutsrqponmlkjihgfedcba",
+        "mxc://matrix.org/abcdefghijklmnopqrstuvwx"
+    ]
+}
+```
diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index 677532c87b..8ee9434c9b 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -808,13 +808,12 @@ class FederationHandler(BaseHandler):
         event_ids = list(extremities.keys())
 
         logger.debug("calling resolve_state_groups in _maybe_backfill")
+        resolve = logcontext.preserve_fn(
+            self.state_handler.resolve_state_groups_for_events
+        )
         states = yield logcontext.make_deferred_yieldable(defer.gatherResults(
-            [
-                logcontext.preserve_fn(self.state_handler.resolve_state_groups)(
-                    room_id, [e]
-                )
-                for e in event_ids
-            ], consumeErrors=True,
+            [resolve(room_id, [e]) for e in event_ids],
+            consumeErrors=True,
         ))
         states = dict(zip(event_ids, [s.state for s in states]))
 
diff --git a/synapse/rest/client/v1/admin.py b/synapse/rest/client/v1/admin.py
index 5022808ea9..0615e5d807 100644
--- a/synapse/rest/client/v1/admin.py
+++ b/synapse/rest/client/v1/admin.py
@@ -289,6 +289,27 @@ class QuarantineMediaInRoom(ClientV1RestServlet):
         defer.returnValue((200, {"num_quarantined": num_quarantined}))
 
 
+class ListMediaInRoom(ClientV1RestServlet):
+    """Lists all of the media in a given room.
+    """
+    PATTERNS = client_path_patterns("/admin/room/(?P<room_id>[^/]+)/media")
+
+    def __init__(self, hs):
+        super(ListMediaInRoom, self).__init__(hs)
+        self.store = hs.get_datastore()
+
+    @defer.inlineCallbacks
+    def on_GET(self, request, room_id):
+        requester = yield self.auth.get_user_by_req(request)
+        is_admin = yield self.auth.is_server_admin(requester.user)
+        if not is_admin:
+            raise AuthError(403, "You are not a server admin")
+
+        local_mxcs, remote_mxcs = yield self.store.get_media_mxcs_in_room(room_id)
+
+        defer.returnValue((200, {"local": local_mxcs, "remote": remote_mxcs}))
+
+
 class ResetPasswordRestServlet(ClientV1RestServlet):
     """Post request to allow an administrator reset password for a user.
     This needs user to have administrator access in Synapse.
@@ -487,3 +508,4 @@ def register_servlets(hs, http_server):
     SearchUsersRestServlet(hs).register(http_server)
     ShutdownRoomRestServlet(hs).register(http_server)
     QuarantineMediaInRoom(hs).register(http_server)
+    ListMediaInRoom(hs).register(http_server)
diff --git a/synapse/rest/media/v1/media_repository.py b/synapse/rest/media/v1/media_repository.py
index 485db8577a..bb79599379 100644
--- a/synapse/rest/media/v1/media_repository.py
+++ b/synapse/rest/media/v1/media_repository.py
@@ -472,8 +472,10 @@ class MediaRepository(object):
 
     @defer.inlineCallbacks
     def generate_local_exact_thumbnail(self, media_id, t_width, t_height,
-                                       t_method, t_type):
-        input_path = self.filepaths.local_media_filepath(media_id)
+                                       t_method, t_type, url_cache):
+        input_path = yield self.media_storage.ensure_media_is_in_local_cache(FileInfo(
+            None, media_id, url_cache=url_cache,
+        ))
 
         thumbnailer = Thumbnailer(input_path)
         t_byte_source = yield make_deferred_yieldable(threads.deferToThread(
@@ -486,6 +488,7 @@ class MediaRepository(object):
                 file_info = FileInfo(
                     server_name=None,
                     file_id=media_id,
+                    url_cache=url_cache,
                     thumbnail=True,
                     thumbnail_width=t_width,
                     thumbnail_height=t_height,
@@ -512,7 +515,9 @@ class MediaRepository(object):
     @defer.inlineCallbacks
     def generate_remote_exact_thumbnail(self, server_name, file_id, media_id,
                                         t_width, t_height, t_method, t_type):
-        input_path = self.filepaths.remote_media_filepath(server_name, file_id)
+        input_path = yield self.media_storage.ensure_media_is_in_local_cache(FileInfo(
+            server_name, file_id, url_cache=False,
+        ))
 
         thumbnailer = Thumbnailer(input_path)
         t_byte_source = yield make_deferred_yieldable(threads.deferToThread(
@@ -570,12 +575,9 @@ class MediaRepository(object):
         if not requirements:
             return
 
-        if server_name:
-            input_path = self.filepaths.remote_media_filepath(server_name, file_id)
-        elif url_cache:
-            input_path = self.filepaths.url_cache_filepath(media_id)
-        else:
-            input_path = self.filepaths.local_media_filepath(media_id)
+        input_path = yield self.media_storage.ensure_media_is_in_local_cache(FileInfo(
+            server_name, file_id, url_cache=url_cache,
+        ))
 
         thumbnailer = Thumbnailer(input_path)
         m_width = thumbnailer.width
diff --git a/synapse/rest/media/v1/media_storage.py b/synapse/rest/media/v1/media_storage.py
index 041ae396cd..e8e8b3986d 100644
--- a/synapse/rest/media/v1/media_storage.py
+++ b/synapse/rest/media/v1/media_storage.py
@@ -18,6 +18,7 @@ from twisted.protocols.basic import FileSender
 
 from ._base import Responder
 
+from synapse.util.file_consumer import BackgroundFileConsumer
 from synapse.util.logcontext import make_deferred_yieldable
 
 import contextlib
@@ -26,6 +27,7 @@ import logging
 import shutil
 import sys
 
+
 logger = logging.getLogger(__name__)
 
 
@@ -151,6 +153,37 @@ class MediaStorage(object):
 
         defer.returnValue(None)
 
+    @defer.inlineCallbacks
+    def ensure_media_is_in_local_cache(self, file_info):
+        """Ensures that the given file is in the local cache. Attempts to
+        download it from storage providers if it isn't.
+
+        Args:
+            file_info (FileInfo)
+
+        Returns:
+            Deferred[str]: Full path to local file
+        """
+        path = self._file_info_to_path(file_info)
+        local_path = os.path.join(self.local_media_directory, path)
+        if os.path.exists(local_path):
+            defer.returnValue(local_path)
+
+        dirname = os.path.dirname(local_path)
+        if not os.path.exists(dirname):
+            os.makedirs(dirname)
+
+        for provider in self.storage_providers:
+            res = yield provider.fetch(path, file_info)
+            if res:
+                with res:
+                    consumer = BackgroundFileConsumer(open(local_path, "w"))
+                    yield res.write_to_consumer(consumer)
+                    yield consumer.wait()
+                defer.returnValue(local_path)
+
+        raise Exception("file could not be found")
+
     def _file_info_to_path(self, file_info):
         """Converts file_info into a relative path.
 
@@ -228,9 +261,8 @@ class FileResponder(Responder):
     def __init__(self, open_file):
         self.open_file = open_file
 
-    @defer.inlineCallbacks
     def write_to_consumer(self, consumer):
-        yield FileSender().beginFileTransfer(self.open_file, consumer)
+        return FileSender().beginFileTransfer(self.open_file, consumer)
 
     def __exit__(self, exc_type, exc_val, exc_tb):
         self.open_file.close()
diff --git a/synapse/rest/media/v1/preview_url_resource.py b/synapse/rest/media/v1/preview_url_resource.py
index 981f01e417..31fe7aa75c 100644
--- a/synapse/rest/media/v1/preview_url_resource.py
+++ b/synapse/rest/media/v1/preview_url_resource.py
@@ -12,6 +12,19 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
+import cgi
+import datetime
+import errno
+import fnmatch
+import itertools
+import logging
+import os
+import re
+import shutil
+import sys
+import traceback
+import ujson as json
+import urlparse
 
 from twisted.web.server import NOT_DONE_YET
 from twisted.internet import defer
@@ -33,18 +46,6 @@ from synapse.http.server import (
 from synapse.util.async import ObservableDeferred
 from synapse.util.stringutils import is_ascii
 
-import os
-import re
-import fnmatch
-import cgi
-import ujson as json
-import urlparse
-import itertools
-import datetime
-import errno
-import shutil
-
-import logging
 logger = logging.getLogger(__name__)
 
 
@@ -286,17 +287,28 @@ class PreviewUrlResource(Resource):
             url_cache=True,
         )
 
-        try:
-            with self.media_storage.store_into_file(file_info) as (f, fname, finish):
+        with self.media_storage.store_into_file(file_info) as (f, fname, finish):
+            try:
                 logger.debug("Trying to get url '%s'" % url)
                 length, headers, uri, code = yield self.client.get_file(
                     url, output_stream=f, max_size=self.max_spider_size,
                 )
+            except Exception as e:
                 # FIXME: pass through 404s and other error messages nicely
+                logger.warn("Error downloading %s: %r", url, e)
+                raise SynapseError(
+                    500, "Failed to download content: %s" % (
+                        traceback.format_exception_only(sys.exc_type, e),
+                    ),
+                    Codes.UNKNOWN,
+                )
+            yield finish()
 
-                yield finish()
-
-            media_type = headers["Content-Type"][0]
+        try:
+            if "Content-Type" in headers:
+                media_type = headers["Content-Type"][0]
+            else:
+                media_type = "application/octet-stream"
             time_now_ms = self.clock.time_msec()
 
             content_disposition = headers.get("Content-Disposition", None)
@@ -336,10 +348,11 @@ class PreviewUrlResource(Resource):
             )
 
         except Exception as e:
-            raise SynapseError(
-                500, ("Failed to download content: %s" % e),
-                Codes.UNKNOWN
-            )
+            logger.error("Error handling downloaded %s: %r", url, e)
+            # TODO: we really ought to delete the downloaded file in this
+            # case, since we won't have recorded it in the db, and will
+            # therefore not expire it.
+            raise
 
         defer.returnValue({
             "media_type": media_type,
diff --git a/synapse/rest/media/v1/thumbnail_resource.py b/synapse/rest/media/v1/thumbnail_resource.py
index 12e84a2b7c..58ada49711 100644
--- a/synapse/rest/media/v1/thumbnail_resource.py
+++ b/synapse/rest/media/v1/thumbnail_resource.py
@@ -164,7 +164,8 @@ class ThumbnailResource(Resource):
 
         # Okay, so we generate one.
         file_path = yield self.media_repo.generate_local_exact_thumbnail(
-            media_id, desired_width, desired_height, desired_method, desired_type
+            media_id, desired_width, desired_height, desired_method, desired_type,
+            url_cache=media_info["url_cache"],
         )
 
         if file_path:
diff --git a/synapse/server.py b/synapse/server.py
index ff8a8fbc46..3173aed1d0 100644
--- a/synapse/server.py
+++ b/synapse/server.py
@@ -66,7 +66,7 @@ from synapse.rest.media.v1.media_repository import (
     MediaRepository,
     MediaRepositoryResource,
 )
-from synapse.state import StateHandler
+from synapse.state import StateHandler, StateResolutionHandler
 from synapse.storage import DataStore
 from synapse.streams.events import EventSources
 from synapse.util import Clock
@@ -102,6 +102,7 @@ class HomeServer(object):
         'v1auth',
         'auth',
         'state_handler',
+        'state_resolution_handler',
         'presence_handler',
         'sync_handler',
         'typing_handler',
@@ -224,6 +225,9 @@ class HomeServer(object):
     def build_state_handler(self):
         return StateHandler(self)
 
+    def build_state_resolution_handler(self):
+        return StateResolutionHandler(self)
+
     def build_presence_handler(self):
         return PresenceHandler(self)
 
diff --git a/synapse/server.pyi b/synapse/server.pyi
index 41416ef252..c3a9a3847b 100644
--- a/synapse/server.pyi
+++ b/synapse/server.pyi
@@ -34,6 +34,9 @@ class HomeServer(object):
     def get_state_handler(self) -> synapse.state.StateHandler:
         pass
 
+    def get_state_resolution_handler(self) -> synapse.state.StateResolutionHandler:
+        pass
+
     def get_deactivate_account_handler(self) -> synapse.handlers.deactivate_account.DeactivateAccountHandler:
         pass
 
diff --git a/synapse/state.py b/synapse/state.py
index 4c8247e7c2..273f9911ca 100644
--- a/synapse/state.py
+++ b/synapse/state.py
@@ -58,7 +58,11 @@ class _StateCacheEntry(object):
     __slots__ = ["state", "state_group", "state_id", "prev_group", "delta_ids"]
 
     def __init__(self, state, state_group, prev_group=None, delta_ids=None):
+        # dict[(str, str), str] map  from (type, state_key) to event_id
         self.state = frozendict(state)
+
+        # the ID of a state group if one and only one is involved.
+        # otherwise, None otherwise?
         self.state_group = state_group
 
         self.prev_group = prev_group
@@ -81,31 +85,19 @@ class _StateCacheEntry(object):
 
 
 class StateHandler(object):
-    """ Responsible for doing state conflict resolution.
+    """Fetches bits of state from the stores, and does state resolution
+    where necessary
     """
 
     def __init__(self, hs):
         self.clock = hs.get_clock()
         self.store = hs.get_datastore()
         self.hs = hs
-
-        # dict of set of event_ids -> _StateCacheEntry.
-        self._state_cache = None
-        self.resolve_linearizer = Linearizer(name="state_resolve_lock")
+        self._state_resolution_handler = hs.get_state_resolution_handler()
 
     def start_caching(self):
-        logger.debug("start_caching")
-
-        self._state_cache = ExpiringCache(
-            cache_name="state_cache",
-            clock=self.clock,
-            max_len=SIZE_OF_CACHE,
-            expiry_ms=EVICTION_TIMEOUT_SECONDS * 1000,
-            iterable=True,
-            reset_expiry_on_get=True,
-        )
-
-        self._state_cache.start()
+        # TODO: remove this shim
+        self._state_resolution_handler.start_caching()
 
     @defer.inlineCallbacks
     def get_current_state(self, room_id, event_type=None, state_key="",
@@ -127,7 +119,7 @@ class StateHandler(object):
             latest_event_ids = yield self.store.get_latest_event_ids_in_room(room_id)
 
         logger.debug("calling resolve_state_groups from get_current_state")
-        ret = yield self.resolve_state_groups(room_id, latest_event_ids)
+        ret = yield self.resolve_state_groups_for_events(room_id, latest_event_ids)
         state = ret.state
 
         if event_type:
@@ -164,7 +156,7 @@ class StateHandler(object):
             latest_event_ids = yield self.store.get_latest_event_ids_in_room(room_id)
 
         logger.debug("calling resolve_state_groups from get_current_state_ids")
-        ret = yield self.resolve_state_groups(room_id, latest_event_ids)
+        ret = yield self.resolve_state_groups_for_events(room_id, latest_event_ids)
         state = ret.state
 
         defer.returnValue(state)
@@ -174,7 +166,7 @@ class StateHandler(object):
         if not latest_event_ids:
             latest_event_ids = yield self.store.get_latest_event_ids_in_room(room_id)
         logger.debug("calling resolve_state_groups from get_current_user_in_room")
-        entry = yield self.resolve_state_groups(room_id, latest_event_ids)
+        entry = yield self.resolve_state_groups_for_events(room_id, latest_event_ids)
         joined_users = yield self.store.get_joined_users_from_state(room_id, entry)
         defer.returnValue(joined_users)
 
@@ -183,7 +175,7 @@ class StateHandler(object):
         if not latest_event_ids:
             latest_event_ids = yield self.store.get_latest_event_ids_in_room(room_id)
         logger.debug("calling resolve_state_groups from get_current_hosts_in_room")
-        entry = yield self.resolve_state_groups(room_id, latest_event_ids)
+        entry = yield self.resolve_state_groups_for_events(room_id, latest_event_ids)
         joined_hosts = yield self.store.get_joined_hosts(room_id, entry)
         defer.returnValue(joined_hosts)
 
@@ -241,7 +233,7 @@ class StateHandler(object):
             defer.returnValue(context)
 
         logger.debug("calling resolve_state_groups from compute_event_context")
-        entry = yield self.resolve_state_groups(
+        entry = yield self.resolve_state_groups_for_events(
             event.room_id, [e for e, _ in event.prev_events],
         )
 
@@ -283,16 +275,16 @@ class StateHandler(object):
         defer.returnValue(context)
 
     @defer.inlineCallbacks
-    @log_function
-    def resolve_state_groups(self, room_id, event_ids):
+    def resolve_state_groups_for_events(self, room_id, event_ids):
         """ Given a list of event_ids this method fetches the state at each
         event, resolves conflicts between them and returns them.
 
+        Args:
+            room_id (str):
+            event_ids (list[str]):
+
         Returns:
-            a Deferred tuple of (`state_group`, `state`, `prev_state`).
-            `state_group` is the name of a state group if one and only one is
-            involved. `state` is a map from (type, state_key) to event, and
-            `prev_state` is a list of event ids.
+            Deferred[_StateCacheEntry]: resolved state
         """
         logger.debug("resolve_state_groups event_ids %s", event_ids)
 
@@ -303,13 +295,7 @@ class StateHandler(object):
             room_id, event_ids
         )
 
-        logger.debug(
-            "resolve_state_groups state_groups %s",
-            state_groups_ids.keys()
-        )
-
-        group_names = frozenset(state_groups_ids.keys())
-        if len(group_names) == 1:
+        if len(state_groups_ids) == 1:
             name, state_list = state_groups_ids.items().pop()
 
             prev_group, delta_ids = yield self.store.get_state_group_delta(name)
@@ -321,6 +307,92 @@ class StateHandler(object):
                 delta_ids=delta_ids,
             ))
 
+        result = yield self._state_resolution_handler.resolve_state_groups(
+            room_id, state_groups_ids, self._state_map_factory,
+        )
+        defer.returnValue(result)
+
+    def _state_map_factory(self, ev_ids):
+        return self.store.get_events(
+            ev_ids, get_prev_content=False, check_redacted=False,
+        )
+
+    def resolve_events(self, state_sets, event):
+        logger.info(
+            "Resolving state for %s with %d groups", event.room_id, len(state_sets)
+        )
+        state_set_ids = [{
+            (ev.type, ev.state_key): ev.event_id
+            for ev in st
+        } for st in state_sets]
+
+        state_map = {
+            ev.event_id: ev
+            for st in state_sets
+            for ev in st
+        }
+
+        with Measure(self.clock, "state._resolve_events"):
+            new_state = resolve_events_with_state_map(state_set_ids, state_map)
+
+        new_state = {
+            key: state_map[ev_id] for key, ev_id in new_state.items()
+        }
+
+        return new_state
+
+
+class StateResolutionHandler(object):
+    """Responsible for doing state conflict resolution.
+
+    Note that the storage layer depends on this handler, so all functions must
+    be storage-independent.
+    """
+    def __init__(self, hs):
+        self.clock = hs.get_clock()
+
+        # dict of set of event_ids -> _StateCacheEntry.
+        self._state_cache = None
+        self.resolve_linearizer = Linearizer(name="state_resolve_lock")
+
+    def start_caching(self):
+        logger.debug("start_caching")
+
+        self._state_cache = ExpiringCache(
+            cache_name="state_cache",
+            clock=self.clock,
+            max_len=SIZE_OF_CACHE,
+            expiry_ms=EVICTION_TIMEOUT_SECONDS * 1000,
+            iterable=True,
+            reset_expiry_on_get=True,
+        )
+
+        self._state_cache.start()
+
+    @defer.inlineCallbacks
+    @log_function
+    def resolve_state_groups(self, room_id, state_groups_ids, state_map_factory):
+        """Resolves conflicts between a set of state groups
+
+        Always generates a new state group (unless we hit the cache), so should
+        not be called for a single state group
+
+        Args:
+            room_id (str): room we are resolving for (used for logging)
+            state_groups_ids (dict[int, dict[(str, str), str]]):
+                 map from state group id to the state in that state group
+                (where 'state' is a map from state key to event id)
+
+        Returns:
+            Deferred[_StateCacheEntry]: resolved state
+        """
+        logger.debug(
+            "resolve_state_groups state_groups %s",
+            state_groups_ids.keys()
+        )
+
+        group_names = frozenset(state_groups_ids.keys())
+
         with (yield self.resolve_linearizer.queue(group_names)):
             if self._state_cache is not None:
                 cache = self._state_cache.get(group_names, None)
@@ -351,15 +423,17 @@ class StateHandler(object):
                 with Measure(self.clock, "state._resolve_events"):
                     new_state = yield resolve_events_with_factory(
                         state_groups_ids.values(),
-                        state_map_factory=lambda ev_ids: self.store.get_events(
-                            ev_ids, get_prev_content=False, check_redacted=False,
-                        ),
+                        state_map_factory=state_map_factory,
                     )
             else:
                 new_state = {
                     key: e_ids.pop() for key, e_ids in state.items()
                 }
 
+            # if the new state matches any of the input state groups, we can
+            # use that state group again. Otherwise we will generate a state_id
+            # which will be used as a cache key for future resolutions, but
+            # not get persisted.
             state_group = None
             new_state_event_ids = frozenset(new_state.values())
             for sg, events in state_groups_ids.items():
@@ -396,30 +470,6 @@ class StateHandler(object):
 
             defer.returnValue(cache)
 
-    def resolve_events(self, state_sets, event):
-        logger.info(
-            "Resolving state for %s with %d groups", event.room_id, len(state_sets)
-        )
-        state_set_ids = [{
-            (ev.type, ev.state_key): ev.event_id
-            for ev in st
-        } for st in state_sets]
-
-        state_map = {
-            ev.event_id: ev
-            for st in state_sets
-            for ev in st
-        }
-
-        with Measure(self.clock, "state._resolve_events"):
-            new_state = resolve_events_with_state_map(state_set_ids, state_map)
-
-        new_state = {
-            key: state_map[ev_id] for key, ev_id in new_state.items()
-        }
-
-        return new_state
-
 
 def _ordered_events(events):
     def key_func(e):
@@ -437,8 +487,8 @@ def resolve_events_with_state_map(state_sets, state_map):
             state_sets.
 
     Returns
-        dict[(str, str), synapse.events.FrozenEvent]:
-            a map from (type, state_key) to event.
+        dict[(str, str), str]:
+            a map from (type, state_key) to event_id.
     """
     if len(state_sets) == 1:
         return state_sets[0]
@@ -460,6 +510,21 @@ def _seperate(state_sets):
     """Takes the state_sets and figures out which keys are conflicted and
     which aren't. i.e., which have multiple different event_ids associated
     with them in different state sets.
+
+    Args:
+        state_sets(list[dict[(str, str), str]]):
+            List of dicts of (type, state_key) -> event_id, which are the
+            different state groups to resolve.
+
+    Returns:
+        (dict[(str, str), str], dict[(str, str), set[str]]):
+            A tuple of (unconflicted_state, conflicted_state), where:
+
+            unconflicted_state is a dict mapping (type, state_key)->event_id
+            for unconflicted state keys.
+
+            conflicted_state is a dict mapping (type, state_key) to a set of
+            event ids for conflicted state keys.
     """
     unconflicted_state = dict(state_sets[0])
     conflicted_state = {}
@@ -500,8 +565,8 @@ def resolve_events_with_factory(state_sets, state_map_factory):
             a Deferred of dict of event_id to event.
 
     Returns
-        Deferred[dict[(str, str), synapse.events.FrozenEvent]]:
-            a map from (type, state_key) to event.
+        Deferred[dict[(str, str), str]]:
+            a map from (type, state_key) to event_id.
     """
     if len(state_sets) == 1:
         defer.returnValue(state_sets[0])
diff --git a/synapse/storage/events.py b/synapse/storage/events.py
index 33fccfa7a8..dd28c2efe3 100644
--- a/synapse/storage/events.py
+++ b/synapse/storage/events.py
@@ -386,11 +386,18 @@ class EventsStore(SQLBaseStore):
                                 if all_single_prev_not_state:
                                     continue
 
-                            state = yield self._calculate_state_delta(
-                                room_id, ev_ctx_rm, new_latest_event_ids
+                            logger.info(
+                                "Calculating state delta for room %s", room_id,
                             )
-                            if state:
-                                current_state_for_room[room_id] = state
+                            current_state = yield self._get_new_state_after_events(
+                                ev_ctx_rm, new_latest_event_ids,
+                            )
+                            if current_state is not None:
+                                delta = yield self._calculate_state_delta(
+                                    room_id, current_state,
+                                )
+                                if delta is not None:
+                                    current_state_for_room[room_id] = delta
 
                 yield self.runInteraction(
                     "persist_events",
@@ -467,20 +474,22 @@ class EventsStore(SQLBaseStore):
         defer.returnValue(new_latest_event_ids)
 
     @defer.inlineCallbacks
-    def _calculate_state_delta(self, room_id, events_context, new_latest_event_ids):
-        """Calculate the new state deltas for a room.
+    def _get_new_state_after_events(self, events_context, new_latest_event_ids):
+        """Calculate the current state dict after adding some new events to
+        a room
 
-        Assumes that we are only persisting events for one room at a time.
+        Args:
+            events_context (list[(EventBase, EventContext)]):
+                events and contexts which are being added to the room
+
+            new_latest_event_ids (iterable[str]):
+                the new forward extremities for the room.
 
         Returns:
-            3-tuple (to_delete, to_insert, new_state) where both are state dicts,
-            i.e. (type, state_key) -> event_id. `to_delete` are the entries to
-            first be deleted from current_state_events, `to_insert` are entries
-            to insert. `new_state` is the full set of state.
-            May return None if there are no changes to be applied.
+            Deferred[dict[(str,str), str]|None]:
+                None if there are no changes to the room state, or
+                a dict of (type, state_key) -> event_id].
         """
-        # Now we need to work out the different state sets for
-        # each state extremities
         state_sets = []
         state_groups = set()
         missing_event_ids = []
@@ -523,12 +532,12 @@ class EventsStore(SQLBaseStore):
                 state_sets.extend(group_to_state.itervalues())
 
         if not new_latest_event_ids:
-            current_state = {}
+            defer.returnValue({})
         elif was_updated:
             if len(state_sets) == 1:
                 # If there is only one state set, then we know what the current
                 # state is.
-                current_state = state_sets[0]
+                defer.returnValue(state_sets[0])
             else:
                 # We work out the current state by passing the state sets to the
                 # state resolution algorithm. It may ask for some events, including
@@ -537,8 +546,7 @@ class EventsStore(SQLBaseStore):
                 # up in the db.
 
                 logger.info(
-                    "Resolving state for %s with %i state sets",
-                    room_id, len(state_sets),
+                    "Resolving state with %i state sets", len(state_sets),
                 )
 
                 events_map = {ev.event_id: ev for ev, _ in events_context}
@@ -567,9 +575,22 @@ class EventsStore(SQLBaseStore):
                     state_sets,
                     state_map_factory=get_events,
                 )
+                defer.returnValue(current_state)
         else:
             return
 
+    @defer.inlineCallbacks
+    def _calculate_state_delta(self, room_id, current_state):
+        """Calculate the new state deltas for a room.
+
+        Assumes that we are only persisting events for one room at a time.
+
+        Returns:
+            3-tuple (to_delete, to_insert, new_state) where both are state dicts,
+            i.e. (type, state_key) -> event_id. `to_delete` are the entries to
+            first be deleted from current_state_events, `to_insert` are entries
+            to insert. `new_state` is the full set of state.
+        """
         existing_state = yield self.get_current_state_ids(room_id)
 
         existing_events = set(existing_state.itervalues())
diff --git a/synapse/storage/room.py b/synapse/storage/room.py
index d91c853070..cf2c4dae39 100644
--- a/synapse/storage/room.py
+++ b/synapse/storage/room.py
@@ -533,73 +533,114 @@ class RoomStore(SQLBaseStore):
         )
         self.is_room_blocked.invalidate((room_id,))
 
+    def get_media_mxcs_in_room(self, room_id):
+        """Retrieves all the local and remote media MXC URIs in a given room
+
+        Args:
+            room_id (str)
+
+        Returns:
+            The local and remote media as a lists of tuples where the key is
+            the hostname and the value is the media ID.
+        """
+        def _get_media_mxcs_in_room_txn(txn):
+            local_mxcs, remote_mxcs = self._get_media_mxcs_in_room_txn(txn, room_id)
+            local_media_mxcs = []
+            remote_media_mxcs = []
+
+            # Convert the IDs to MXC URIs
+            for media_id in local_mxcs:
+                local_media_mxcs.append("mxc://%s/%s" % (self.hostname, media_id))
+            for hostname, media_id in remote_mxcs:
+                remote_media_mxcs.append("mxc://%s/%s" % (hostname, media_id))
+
+            return local_media_mxcs, remote_media_mxcs
+        return self.runInteraction("get_media_ids_in_room", _get_media_mxcs_in_room_txn)
+
     def quarantine_media_ids_in_room(self, room_id, quarantined_by):
         """For a room loops through all events with media and quarantines
         the associated media
         """
-        def _get_media_ids_in_room(txn):
-            mxc_re = re.compile("^mxc://([^/]+)/([^/#?]+)")
+        def _quarantine_media_in_room_txn(txn):
+            local_mxcs, remote_mxcs = self._get_media_mxcs_in_room_txn(txn, room_id)
+            total_media_quarantined = 0
 
-            next_token = self.get_current_events_token() + 1
+            # Now update all the tables to set the quarantined_by flag
 
-            total_media_quarantined = 0
+            txn.executemany("""
+                UPDATE local_media_repository
+                SET quarantined_by = ?
+                WHERE media_id = ?
+            """, ((quarantined_by, media_id) for media_id in local_mxcs))
 
-            while next_token:
-                sql = """
-                    SELECT stream_ordering, content FROM events
-                    WHERE room_id = ?
-                        AND stream_ordering < ?
-                        AND contains_url = ? AND outlier = ?
-                    ORDER BY stream_ordering DESC
-                    LIMIT ?
+            txn.executemany(
                 """
-                txn.execute(sql, (room_id, next_token, True, False, 100))
-
-                next_token = None
-                local_media_mxcs = []
-                remote_media_mxcs = []
-                for stream_ordering, content_json in txn:
-                    next_token = stream_ordering
-                    content = json.loads(content_json)
-
-                    content_url = content.get("url")
-                    thumbnail_url = content.get("info", {}).get("thumbnail_url")
-
-                    for url in (content_url, thumbnail_url):
-                        if not url:
-                            continue
-                        matches = mxc_re.match(url)
-                        if matches:
-                            hostname = matches.group(1)
-                            media_id = matches.group(2)
-                            if hostname == self.hostname:
-                                local_media_mxcs.append(media_id)
-                            else:
-                                remote_media_mxcs.append((hostname, media_id))
-
-                # Now update all the tables to set the quarantined_by flag
-
-                txn.executemany("""
-                    UPDATE local_media_repository
+                    UPDATE remote_media_cache
                     SET quarantined_by = ?
-                    WHERE media_id = ?
-                """, ((quarantined_by, media_id) for media_id in local_media_mxcs))
-
-                txn.executemany(
-                    """
-                        UPDATE remote_media_cache
-                        SET quarantined_by = ?
-                        WHERE media_origin = ? AND media_id = ?
-                    """,
-                    (
-                        (quarantined_by, origin, media_id)
-                        for origin, media_id in remote_media_mxcs
-                    )
+                    WHERE media_origin = ? AND media_id = ?
+                """,
+                (
+                    (quarantined_by, origin, media_id)
+                    for origin, media_id in remote_mxcs
                 )
+            )
 
-                total_media_quarantined += len(local_media_mxcs)
-                total_media_quarantined += len(remote_media_mxcs)
+            total_media_quarantined += len(local_mxcs)
+            total_media_quarantined += len(remote_mxcs)
 
             return total_media_quarantined
 
-        return self.runInteraction("get_media_ids_in_room", _get_media_ids_in_room)
+        return self.runInteraction(
+            "quarantine_media_in_room",
+            _quarantine_media_in_room_txn,
+        )
+
+    def _get_media_mxcs_in_room_txn(self, txn, room_id):
+        """Retrieves all the local and remote media MXC URIs in a given room
+
+        Args:
+            txn (cursor)
+            room_id (str)
+
+        Returns:
+            The local and remote media as a lists of tuples where the key is
+            the hostname and the value is the media ID.
+        """
+        mxc_re = re.compile("^mxc://([^/]+)/([^/#?]+)")
+
+        next_token = self.get_current_events_token() + 1
+        local_media_mxcs = []
+        remote_media_mxcs = []
+
+        while next_token:
+            sql = """
+                SELECT stream_ordering, content FROM events
+                WHERE room_id = ?
+                    AND stream_ordering < ?
+                    AND contains_url = ? AND outlier = ?
+                ORDER BY stream_ordering DESC
+                LIMIT ?
+            """
+            txn.execute(sql, (room_id, next_token, True, False, 100))
+
+            next_token = None
+            for stream_ordering, content_json in txn:
+                next_token = stream_ordering
+                content = json.loads(content_json)
+
+                content_url = content.get("url")
+                thumbnail_url = content.get("info", {}).get("thumbnail_url")
+
+                for url in (content_url, thumbnail_url):
+                    if not url:
+                        continue
+                    matches = mxc_re.match(url)
+                    if matches:
+                        hostname = matches.group(1)
+                        media_id = matches.group(2)
+                        if hostname == self.hostname:
+                            local_media_mxcs.append(media_id)
+                        else:
+                            remote_media_mxcs.append((hostname, media_id))
+
+        return local_media_mxcs, remote_media_mxcs
diff --git a/tests/rest/media/__init__.py b/tests/rest/media/__init__.py
new file mode 100644
index 0000000000..a354d38ca8
--- /dev/null
+++ b/tests/rest/media/__init__.py
@@ -0,0 +1,14 @@
+# -*- coding: utf-8 -*-
+# Copyright 2018 New Vector Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
diff --git a/tests/rest/media/v1/__init__.py b/tests/rest/media/v1/__init__.py
new file mode 100644
index 0000000000..a354d38ca8
--- /dev/null
+++ b/tests/rest/media/v1/__init__.py
@@ -0,0 +1,14 @@
+# -*- coding: utf-8 -*-
+# Copyright 2018 New Vector Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
diff --git a/tests/rest/media/v1/test_media_storage.py b/tests/rest/media/v1/test_media_storage.py
new file mode 100644
index 0000000000..eef38b6781
--- /dev/null
+++ b/tests/rest/media/v1/test_media_storage.py
@@ -0,0 +1,86 @@
+# -*- coding: utf-8 -*-
+# Copyright 2018 New Vector Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+
+from twisted.internet import defer
+
+from synapse.rest.media.v1._base import FileInfo
+from synapse.rest.media.v1.media_storage import MediaStorage
+from synapse.rest.media.v1.filepath import MediaFilePaths
+from synapse.rest.media.v1.storage_provider import FileStorageProviderBackend
+
+from mock import Mock
+
+from tests import unittest
+
+import os
+import shutil
+import tempfile
+
+
+class MediaStorageTests(unittest.TestCase):
+    def setUp(self):
+        self.test_dir = tempfile.mkdtemp(prefix="synapse-tests-")
+
+        self.primary_base_path = os.path.join(self.test_dir, "primary")
+        self.secondary_base_path = os.path.join(self.test_dir, "secondary")
+
+        hs = Mock()
+        hs.config.media_store_path = self.primary_base_path
+
+        storage_providers = [FileStorageProviderBackend(
+            hs, self.secondary_base_path
+        )]
+
+        self.filepaths = MediaFilePaths(self.primary_base_path)
+        self.media_storage = MediaStorage(
+            self.primary_base_path, self.filepaths, storage_providers,
+        )
+
+    def tearDown(self):
+        shutil.rmtree(self.test_dir)
+
+    @defer.inlineCallbacks
+    def test_ensure_media_is_in_local_cache(self):
+        media_id = "some_media_id"
+        test_body = "Test\n"
+
+        # First we create a file that is in a storage provider but not in the
+        # local primary media store
+        rel_path = self.filepaths.local_media_filepath_rel(media_id)
+        secondary_path = os.path.join(self.secondary_base_path, rel_path)
+
+        os.makedirs(os.path.dirname(secondary_path))
+
+        with open(secondary_path, "w") as f:
+            f.write(test_body)
+
+        # Now we run ensure_media_is_in_local_cache, which should copy the file
+        # to the local cache.
+        file_info = FileInfo(None, media_id)
+        local_path = yield self.media_storage.ensure_media_is_in_local_cache(file_info)
+
+        self.assertTrue(os.path.exists(local_path))
+
+        # Asserts the file is under the expected local cache directory
+        self.assertEquals(
+            os.path.commonprefix([self.primary_base_path, local_path]),
+            self.primary_base_path,
+        )
+
+        with open(local_path) as f:
+            body = f.read()
+
+        self.assertEqual(test_body, body)
diff --git a/tests/test_state.py b/tests/test_state.py
index feb84f3d48..d16e1b3b8b 100644
--- a/tests/test_state.py
+++ b/tests/test_state.py
@@ -19,7 +19,7 @@ from twisted.internet import defer
 from synapse.events import FrozenEvent
 from synapse.api.auth import Auth
 from synapse.api.constants import EventTypes, Membership
-from synapse.state import StateHandler
+from synapse.state import StateHandler, StateResolutionHandler
 
 from .utils import MockClock
 
@@ -148,11 +148,13 @@ class StateTestCase(unittest.TestCase):
         )
         hs = Mock(spec_set=[
             "get_datastore", "get_auth", "get_state_handler", "get_clock",
+            "get_state_resolution_handler",
         ])
         hs.get_datastore.return_value = self.store
         hs.get_state_handler.return_value = None
         hs.get_clock.return_value = MockClock()
         hs.get_auth.return_value = Auth(hs)
+        hs.get_state_resolution_handler = lambda: StateResolutionHandler(hs)
 
         self.store.get_next_state_group.side_effect = Mock
         self.store.get_state_group_delta.return_value = (None, None)