Clean up the blacklist/whitelist handling.

Always set the config key with an empty list, even if a list isn't specified.
This means that the codepaths are the same for both the empty list and
for a missing key. Since the behaviour is the same for both cases this
makes the code somewhat easier to reason about.

synapse/config/repository.py

@@ -100,13 +100,13 @@ class ContentRepositoryConfig(Config):
                     "to work"
                 )
 
-            if "url_preview_ip_range_whitelist" in config:
             self.url_preview_ip_range_whitelist = IPSet(
-                    config["url_preview_ip_range_whitelist"]
+                config.get("url_preview_ip_range_whitelist", ())
             )
 
-            if "url_preview_url_blacklist" in config:
-                self.url_preview_url_blacklist = config["url_preview_url_blacklist"]
+            self.url_preview_url_blacklist = config.get(
+                "url_preview_url_blacklist", ()
+            )
 
     def default_config(self, **kwargs):
         media_store = self.default_path("media_store")

synapse/http/client.py

@@ -380,7 +380,6 @@ class CaptchaServerHttpClient(SimpleHttpClient):
 class SpiderEndpointFactory(object):
     def __init__(self, hs):
         self.blacklist = hs.config.url_preview_ip_range_blacklist
-        if hasattr(hs.config, "url_preview_ip_range_whitelist"):
         self.whitelist = hs.config.url_preview_ip_range_whitelist
         self.policyForHTTPS = hs.get_http_client_context_factory()
 

synapse/rest/media/v1/preview_url_resource.py

@@ -56,7 +56,6 @@ class PreviewUrlResource(Resource):
         self.client = SpiderHttpClient(hs)
         self.media_repo = media_repo
 
-        if hasattr(hs.config, "url_preview_url_blacklist"):
         self.url_preview_url_blacklist = hs.config.url_preview_url_blacklist
 
         # simple memory cache mapping urls to OG metadata
@@ -86,8 +85,6 @@ class PreviewUrlResource(Resource):
         else:
             ts = self.clock.time_msec()
 
-        # impose the URL pattern blacklist
-        if hasattr(self, "url_preview_url_blacklist"):
         url_tuple = urlparse.urlsplit(url)
         for entry in self.url_preview_url_blacklist:
             match = True