Add basic setup for tild.es link-shortener

Links aren't displayed/used anywhere yet, but this should be the basic
setup needed for a simple link-shortener on the tild.es domain.

Currently, it will support two uses:

* https://tild.es/asdf - redirect to topic with id "asdf"
* https://tild.es/~asdf - redirect to group "~asdf"

salt/salt/nginx/shortener-config.sls

@@ -0,0 +1,16 @@
+/etc/nginx/sites-available/tildes-shortener.conf:
+  file.managed:
+    - source: salt://nginx/tildes-shortener.conf.jinja2
+    - template: jinja
+    - user: root
+    - group: root
+    - mode: 644
+    - makedirs: True
+
+/etc/nginx/sites-enabled/tildes-shortener.conf:
+  file.symlink:
+    - target: /etc/nginx/sites-available/tildes-shortener.conf
+    - makedirs: True
+    - user: root
+    - group: root
+    - mode: 644

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

@@ -0,0 +1,23 @@
+server {
+    listen 443 ssl http2;
+    listen [::]:443 ssl http2;
+
+    add_header Strict-Transport-Security "max-age={{ pillar['hsts_max_age'] }}; includeSubDomains; preload" always;
+
+    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;
+
+    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/;
+    }
+}

salt/salt/top.sls

@@ -28,6 +28,7 @@ base:
     - development
     - prometheus
   'prod':
+    - nginx.shortener-config
     - nginx.static-sites-config
     - raven
     - prod-config

tildes/tildes/routes.py

@@ -90,6 +90,12 @@ def includeme(config: Configurator) -> None:
     with config.route_prefix_context("/api/web"):
         add_intercooler_routes(config)
 
+    # Add routes for the link-shortener under the /shortener path
+    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)
+
 
 def add_intercooler_routes(config: Configurator) -> None:
     """Set up all routes for the (internal-use) Intercooler API endpoints."""

tildes/tildes/views/shortener.py

@@ -0,0 +1,28 @@
+# Copyright (c) 2018 Tildes contributors <code@tildes.net>
+# SPDX-License-Identifier: AGPL-3.0-or-later
+
+"""Views related to the link shortener."""
+
+from pyramid.httpexceptions import HTTPFound
+from pyramid.request import Request
+from pyramid.response import Response
+from pyramid.view import view_config
+
+
+@view_config(route_name="shortener")
+def get_shortener(request: Request) -> Response:
+    """Display a message if someone just visits the base shortener domain."""
+    # pylint: disable=unused-argument
+    return Response("Link-shortener for tildes.net")
+
+
+@view_config(route_name="shortener_group")
+def get_shortener_group(request: Request) -> HTTPFound:
+    """Redirect to the base path of a group."""
+    raise HTTPFound(location=f"/~{request.context.path}")
+
+
+@view_config(route_name="shortener_topic")
+def get_shortener_topic(request: Request) -> HTTPFound:
+    """Redirect to the full permalink for a topic."""
+    raise HTTPFound(location=request.context.permalink)