automatically resync media, and don't send media server already has (#583)

anki/media.py

@@ -466,3 +466,17 @@ create table log (fname text primary key, type int);
         assert not self.db.scalar("select count() from log")
         cnt = self.db.scalar("select count() from media")
         return cnt
+
+    def forceResync(self):
+        self.db.execute("delete from media")
+        self.db.execute("delete from log")
+        self.db.execute("update meta set usn = 0, dirMod = 0")
+        self.db.commit()
+
+    def removeExisting(self, files):
+        "Remove files from list of files to sync."
+        # add temporary index
+        self.db.execute("create index if not exists ix_fname_tmp on log(fname)")
+        self.db.executemany("delete from log where fname=?", ((f,) for f in files))
+        self.db.execute("drop index ix_fname_tmp")
+        self.db.commit()

anki/sync.py

@@ -656,10 +656,17 @@ class MediaSyncer(object):
     def sync(self, mediaUsn):
         # step 1: check if there have been any changes
         runHook("sync", "findMedia")
-        self.col.media.findChanges()
         lusn = self.col.media.usn()
+        # if first sync or resync, clear list of files we think we've sent
+        if not lusn:
+            self.col.media.forceResync()
+        self.col.media.findChanges()
         if lusn == mediaUsn and not self.col.media.hasChanged():
             return "noChanges"
+        # step 1.5: if resyncing, we need to get the list of files the server
+        # has and remove them from our local list of files to sync
+        files = self.server.mediaList()
+        self.col.media.removeExisting(files)
         # step 2: send/recv deletions
         runHook("sync", "removeMedia")
         lrem = self.removed()
@@ -691,6 +698,8 @@ class MediaSyncer(object):
         s = self.server.mediaSanity()
         c = self.mediaSanity()
         if c != s:
+            # if the sanity check failed, force a resync
+            self.col.media.forceResync()
             raise Exception("""\
 Media sanity check failed. Please copy and paste the text below:\n%s\n%s""" %
                             (c, s))
@@ -739,6 +748,10 @@ class RemoteMediaServer(HttpSyncer):
         return json.loads(
             self.req("mediaSanity"))
 
+    def mediaList(self):
+        return json.loads(
+            self.req("mediaList"))
+
     # only for unit tests
     def mediatest(self, n):
         return json.loads(