refactor: Extract MessageDict.hydrate_recipient_info().

This is a first step to eventually slimming the message cache,
but there are still some moving parts there to be worked through.

The more immediate benefit of extracting this function is that
we can put tests on it.  Also, it isolates some functionality
that may go away as our clients gets smarter.

zerver/lib/message.py

@@ -171,32 +171,6 @@ class MessageDict(object):
             id=sender_id,
             realm_id=sender_realm_id))
 
-        display_recipient = get_display_recipient_by_id(
-            recipient_id,
-            recipient_type,
-            recipient_type_id
-        )
-
-        if recipient_type == Recipient.STREAM:
-            display_type = "stream"
-        elif recipient_type in (Recipient.HUDDLE, Recipient.PERSONAL):
-            assert not isinstance(display_recipient, Text)
-            display_type = "private"
-            if len(display_recipient) == 1:
-                # add the sender in if this isn't a message between
-                # someone and themself, preserving ordering
-                recip = {'email': sender_email,
-                         'full_name': sender_full_name,
-                         'short_name': sender_short_name,
-                         'id': sender_id,
-                         'is_mirror_dummy': sender_is_mirror_dummy}
-                if recip['email'] < display_recipient[0]['email']:
-                    display_recipient = [recip, display_recipient[0]]
-                elif recip['email'] > display_recipient[0]['email']:
-                    display_recipient = [display_recipient[0], recip]
-        else:
-            raise AssertionError("Invalid recipient type %s" % (recipient_type,))
-
         obj = dict(
             id                = message_id,
             sender_email      = sender_email,
@@ -204,16 +178,23 @@ class MessageDict(object):
             sender_short_name = sender_short_name,
             sender_realm_str  = sender_realm_str,
             sender_id         = sender_id,
-            type              = display_type,
-            display_recipient = display_recipient,
+            recipient_type_id = recipient_type_id,
+            recipient_type    = recipient_type,
             recipient_id      = recipient_id,
             subject           = subject,
             timestamp         = datetime_to_timestamp(pub_date),
             avatar_url        = avatar_url,
             client            = sending_client_name)
 
-        if obj['type'] == 'stream':
-            obj['stream_id'] = recipient_type_id
+        obj['raw_display_recipient'] = get_display_recipient_by_id(
+            recipient_id,
+            recipient_type,
+            recipient_type_id
+        )
+
+        obj['sender_is_mirror_dummy'] = sender_is_mirror_dummy
+
+        MessageDict.hydrate_recipient_info(obj)
 
         obj['subject_links'] = bugdown.subject_links(sender_realm_id, subject)
 
@@ -264,6 +245,55 @@ class MessageDict(object):
                             for reaction in reactions]
         return obj
 
+    @staticmethod
+    def hydrate_recipient_info(obj):
+        # type: (Dict[str, Any]) -> None
+        '''
+        This method hyrdrates recipient info with things
+        like full names and emails of senders.  Eventually
+        our clients should be able to hyrdrate these fields
+        themselves with info they already have on users.
+        '''
+
+        display_recipient = obj['raw_display_recipient']
+        recipient_type = obj['recipient_type']
+        recipient_type_id = obj['recipient_type_id']
+        sender_is_mirror_dummy = obj['sender_is_mirror_dummy']
+
+        del obj['raw_display_recipient']
+        del obj['recipient_type']
+        del obj['recipient_type_id']
+        del obj['sender_is_mirror_dummy']
+
+        sender_email = obj['sender_email']
+        sender_full_name = obj['sender_full_name']
+        sender_short_name = obj['sender_short_name']
+        sender_id = obj['sender_id']
+
+        if recipient_type == Recipient.STREAM:
+            display_type = "stream"
+        elif recipient_type in (Recipient.HUDDLE, Recipient.PERSONAL):
+            assert not isinstance(display_recipient, Text)
+            display_type = "private"
+            if len(display_recipient) == 1:
+                # add the sender in if this isn't a message between
+                # someone and themself, preserving ordering
+                recip = {'email': sender_email,
+                         'full_name': sender_full_name,
+                         'short_name': sender_short_name,
+                         'id': sender_id,
+                         'is_mirror_dummy': sender_is_mirror_dummy}
+                if recip['email'] < display_recipient[0]['email']:
+                    display_recipient = [recip, display_recipient[0]]
+                elif recip['email'] > display_recipient[0]['email']:
+                    display_recipient = [display_recipient[0], recip]
+        else:
+            raise AssertionError("Invalid recipient type %s" % (recipient_type,))
+
+        obj['display_recipient'] = display_recipient
+        obj['type'] = display_type
+        if obj['type'] == 'stream':
+            obj['stream_id'] = recipient_type_id
 
 class ReactionDict(object):
     @staticmethod

zerver/tests/test_messages.py

@@ -2608,3 +2608,77 @@ class SoftDeactivationMessageTest(ZulipTestCase):
         assert_um_count(long_term_idle_user, soft_deactivated_user_msg_count)
         assert_um_count(cordelia, general_user_msg_count + 1)
         assert_last_um_content(cordelia, force_text(message))
+
+class MessageHydrationTest(ZulipTestCase):
+    def test_hydrate_stream_recipient_info(self):
+        # type: () -> None
+        realm = get_realm('zulip')
+        cordelia = self.example_user('cordelia')
+
+        stream_id = get_stream('Verona', realm).id
+
+        obj = dict(
+            raw_display_recipient='Verona',
+            recipient_type=Recipient.STREAM,
+            recipient_type_id=stream_id,
+            sender_is_mirror_dummy=False,
+            sender_email=cordelia.email,
+            sender_full_name=cordelia.full_name,
+            sender_short_name=cordelia.short_name,
+            sender_id=cordelia.id,
+        )
+
+        MessageDict.hydrate_recipient_info(obj)
+
+        self.assertEqual(obj, dict(
+            display_recipient='Verona',
+            stream_id=stream_id,
+            type='stream',
+            sender_email=cordelia.email,
+            sender_full_name=cordelia.full_name,
+            sender_short_name=cordelia.short_name,
+            sender_id=cordelia.id,
+        ))
+
+    def test_hydrate_pm_recipient_info(self):
+        # type: () -> None
+        cordelia = self.example_user('cordelia')
+
+        obj = dict(
+            raw_display_recipient=[
+                dict(
+                    email='aaron@example.com',
+                    full_name='Aaron Smith',
+                ),
+            ],
+            recipient_type=Recipient.PERSONAL,
+            recipient_type_id=None,
+            sender_is_mirror_dummy=False,
+            sender_email=cordelia.email,
+            sender_full_name=cordelia.full_name,
+            sender_short_name=cordelia.short_name,
+            sender_id=cordelia.id,
+        )
+
+        MessageDict.hydrate_recipient_info(obj)
+
+        self.assertEqual(obj, dict(
+            display_recipient=[
+                dict(
+                    email='aaron@example.com',
+                    full_name='Aaron Smith',
+                ),
+                dict(
+                    email=cordelia.email,
+                    full_name=cordelia.full_name,
+                    id=cordelia.id,
+                    short_name=cordelia.short_name,
+                    is_mirror_dummy=False,
+                ),
+            ],
+            type='private',
+            sender_email=cordelia.email,
+            sender_full_name=cordelia.full_name,
+            sender_short_name=cordelia.short_name,
+            sender_id=cordelia.id,
+        ))