Change tild.es to nginx redirect instead of proxy

Previously tild.es urls would proxy_pass through to the views inside the
Pyramid app, but this caused strange behavior in some cases. For
example, anything that caused a 404 response would end up in a broken
page that still appeared to be on the tild.es domain, but would be an
HTML-only page coming from the app, since the CSS and JS would not be
available.

This method is still a bit weird in some ways (now you'll end up on a
404 page at https://tildes.net/shortener/... instead), but I think it's
an improvement overall.

salt/salt/nginx/tildes-shortener.conf.jinja2

@@ -1,26 +1,27 @@
 server {
-    # remove trailing slash from addresses
-    rewrite ^/(.*)/$ https://$host/$1 permanent;
-
     listen 443 ssl http2;
     listen [::]:443 ssl http2;
 
+    server_name tild.es;
+
+    keepalive_timeout 5;
+
     add_header Strict-Transport-Security "max-age={{ pillar['hsts_max_age'] }}; includeSubDomains; preload" always;
 
+    # Are these security headers unnecessary when we're just redirecting?
     add_header X-Content-Type-Options "nosniff" always;
     add_header X-Frame-Options "SAMEORIGIN" always;
     add_header X-Xss-Protection "1; mode=block" always;
     add_header Referrer-Policy "same-origin" always;
 
-    server_name tild.es;
-
-    keepalive_timeout 5;
+    # Exact location match to redirect the root url to tildes.net
+    location = / {
+        return 301 https://tildes.net;
+    }
 
+    # Will match all addresses *except* the root
     location / {
-        proxy_set_header Host $host;
-        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
-        proxy_set_header X-Forwarded-Proto $scheme;
-        proxy_redirect off;
-        proxy_pass http://app_server/shortener/;
+        # Strip any trailing slash while redirecting
+        rewrite ^/(.*)/?$ https://tildes.net/shortener/$1 permanent;
     }
 }

tildes/tildes/routes.py

@@ -109,9 +109,6 @@ def includeme(config: Configurator) -> None:
         add_intercooler_routes(config)
 
     # Add routes for the link-shortener under the /shortener path
-    # The trailing slash is required for the base /shortener/ path because of the way
-    # nginx's proxy_pass will forward the urls from the shortener
-    config.add_route("shortener", "/shortener/")
     with config.route_prefix_context("/shortener"):
         config.add_route("shortener_group", "/~{group_path}", factory=group_by_path)
         config.add_route("shortener_topic", "/{topic_id36}", factory=topic_by_id36)

tildes/tildes/views/shortener.py

@@ -4,19 +4,12 @@
 """Views related to the link shortener."""
 
 from mypy_extensions import NoReturn
-from pyramid.httpexceptions import HTTPFound, HTTPMovedPermanently
+from pyramid.httpexceptions import HTTPMovedPermanently
 from pyramid.request import Request
 from pyramid.security import NO_PERMISSION_REQUIRED
 from pyramid.view import view_config
 
 
-@view_config(route_name="shortener", permission=NO_PERMISSION_REQUIRED)
-def get_shortener(request: Request) -> NoReturn:
-    """Redirect to the site if someone just visits the base shortener domain."""
-    # pylint: disable=unused-argument
-    raise HTTPFound(location="https://tildes.net")
-
-
 @view_config(route_name="shortener_group", permission=NO_PERMISSION_REQUIRED)
 def get_shortener_group(request: Request) -> NoReturn:
     """Redirect to the base path of a group."""