mastodon: read max toot size from v2 API

relates to snarfed#1533

models.py

@@ -247,11 +247,15 @@ def __getattr__(self, name):
     elif self.key.kind() == 'Mastodon':
       args = (auth_entity.instance(),) + args
       inst = auth_entity.app.get().instance_info
+      if inst:
+        j = json_loads(inst)
+        truncate_text_length = j.get("configuration", {}).get('statuses', {}).get('max_characters', None) or j.get('max_toot_chars', None)
+      else:
+        truncate_text_length = None
       kwargs = {
         'user_id': json_loads(auth_entity.user_json).get('id'),
         # https://docs-develop.pleroma.social/backend/API/differences_in_mastoapi_responses/#instance
-        'truncate_text_length':
-          json_loads(inst).get('max_toot_chars') if inst else None,
+        'truncate_text_length': truncate_text_length,
       }
     elif self.key.kind() == 'Twitter':
       kwargs = {'username': self.key_id()}

tests/test_mastodon.py

@@ -1,10 +1,8 @@
 """Unit tests for mastodon.py.
 """
-from granary.mastodon import API_BLOCKS, API_SEARCH
-from granary.tests.test_mastodon import STATUS
+from granary.mastodon import API_BLOCKS
 from oauth_dropins import mastodon as oauth_mastodon
-from oauth_dropins.webutil import util
-from oauth_dropins.webutil.util import json_dumps, json_loads
+from oauth_dropins.webutil.util import json_dumps
 
 from . import testutil
 from mastodon import Mastodon
@@ -59,3 +57,9 @@ def test_gr_class_with_max_toot_chars(self):
     app.instance_info = '{"max_toot_chars": 999}'
     app.put()
     self.assert_equals(999, self.m.gr_source.TRUNCATE_TEXT_LENGTH)
+
+  def test_gr_class_with_max_characters(self):
+    app = self.auth_entity.app.get()
+    app.instance_info = '{"configuration": {"statuses": {"max_characters": 888}}}'
+    app.put()
+    self.assert_equals(888, self.m.gr_source.TRUNCATE_TEXT_LENGTH)