messages: Modify access_message for is_history_public_to_subscribers.

This completes the Message side of #2745.

zerver/lib/message.py

@@ -482,17 +482,28 @@ def access_message(user_profile: UserProfile, message_id: int) -> Tuple[Message,
             # You can't access private messages you didn't receive
             raise JsonableError(_("Invalid message(s)"))
         stream = Stream.objects.get(id=message.recipient.type_id)
-        if not stream.is_public():
-            # You can't access messages sent to invite-only streams
-            # that you didn't receive
-            raise JsonableError(_("Invalid message(s)"))
-        # So the message is to a public stream
         if stream.realm != user_profile.realm:
             # You can't access public stream messages in other realms
             raise JsonableError(_("Invalid message(s)"))
 
-    # Otherwise, the message must have been sent to a public
-    # stream in your realm, so return the message, user_message pair
+        if not stream.is_public():
+            if not stream.is_history_public_to_subscribers():
+                # You can't access messages sent to invite-only streams
+                # that you didn't receive
+                raise JsonableError(_("Invalid message(s)"))
+
+            # This stream is an invite-only stream where message
+            # history is available to subscribers.  So we check if
+            # you're subscribed.
+            if not Subscription.objects.filter(user_profile=user_profile, active=True,
+                                               recipient=message.recipient).exists():
+                raise JsonableError(_("Invalid message(s)"))
+
+            # You are subscribed, so let this fall through to the public stream case.
+        else:
+            # Otherwise, the message was sent to a public stream in
+            # your realm, so return the message, user_message pair
+            pass
     return (message, user_message)
 
 def render_markdown(message: Message,

zerver/tests/test_messages.py

@@ -2262,6 +2262,7 @@ class MirroredMessageUsersTest(ZulipTestCase):
         self.assertTrue(bob.is_mirror_dummy)
 
 class StarTests(ZulipTestCase):
+    """This is also the main test for access_message"""
 
     def change_star(self, messages: List[int], add: bool=True, **kwargs: Any) -> HttpResponse:
         return self.client_post("/json/messages/flags",
@@ -2405,6 +2406,18 @@ class StarTests(ZulipTestCase):
         result = self.change_star(message_ids)
         self.assert_json_error(result, 'Invalid message(s)')
 
+        with self.settings(PRIVATE_STREAM_HISTORY_FOR_SUBSCRIBERS=True):
+            # With PRIVATE_STREAM_HISTORY_FOR_SUBSCRIBERS, you still
+            # can't see it if you didn't receive the message and are
+            # not subscribed.
+            result = self.change_star(message_ids)
+            self.assert_json_error(result, 'Invalid message(s)')
+
+            # But if you subscribe, then you can star the message
+            self.subscribe(self.example_user("cordelia"), stream_name)
+            result = self.change_star(message_ids)
+            self.assert_json_success(result)
+
     def test_new_message(self) -> None:
         """
         New messages aren't starred.