Allow configuring the Riot URL used in notification emails

The URLs used for notification emails were hardcoded to use either matrix.to
or vector.im; but for self-hosted setups where Riot is also self-hosted it
may be desirable to allow configuring an alternative Riot URL.

Fixes #1809.

Signed-off-by: Adrian Perez de Castro <aperez@igalia.com>

synapse/config/emailconfig.py

@@ -68,6 +68,9 @@ class EmailConfig(Config):
             self.email_notif_for_new_users = email_config.get(
                 "notif_for_new_users", True
             )
+            self.email_riot_base_url = email_config.get(
+                "riot_base_url", None
+            )
             if "app_name" in email_config:
                 self.email_app_name = email_config["app_name"]
             else:
@@ -85,6 +88,9 @@ class EmailConfig(Config):
     def default_config(self, config_dir_path, server_name, **kwargs):
         return """
         # Enable sending emails for notification events
+        # Defining a custom URL for Riot is only needed if email notifications
+        # should contain links to a self-hosted installation of Riot; when set
+        # the "app_name" setting is ignored.
         #email:
         #   enable_notifs: false
         #   smtp_host: "localhost"
@@ -95,4 +101,5 @@ class EmailConfig(Config):
         #   notif_template_html: notif_mail.html
         #   notif_template_text: notif_mail.txt
         #   notif_for_new_users: True
+        #   riot_base_url: "http://localhost/riot"
         """

synapse/push/mailer.py

@@ -439,15 +439,23 @@ class Mailer(object):
                 })
 
     def make_room_link(self, room_id):
-        # need /beta for Universal Links to work on iOS
-        if self.app_name == "Vector":
-            return "https://vector.im/beta/#/room/%s" % (room_id,)
+        if self.hs.config.email_riot_base_url:
+            base_url = self.hs.config.email_riot_base_url
+        elif self.app_name == "Vector":
+            # need /beta for Universal Links to work on iOS
+            base_url = "https://vector.im/beta/#/room"
         else:
-            return "https://matrix.to/#/%s" % (room_id,)
+            base_url = "https://matrix.to/#"
+        return "%s/%s" % (base_url, room_id)
 
     def make_notif_link(self, notif):
-        # need /beta for Universal Links to work on iOS
-        if self.app_name == "Vector":
+        if self.hs.config.email_riot_base_url:
+            return "%s/#/room/%s/%s" % (
+                self.hs.config.email_riot_base_url,
+                notif['room_id'], notif['event_id']
+            )
+        elif self.app_name == "Vector":
+            # need /beta for Universal Links to work on iOS
             return "https://vector.im/beta/#/room/%s/%s" % (
                 notif['room_id'], notif['event_id']
             )