add "localhost" to ALLOWED_HOSTS

if PAPERLESS_URL is set and ALLOWED_HOSTS is NOT set

Signed-off-by: Florian Brandes <florian.brandes@posteo.de>

docs/configuration.rst

@@ -170,6 +170,9 @@ PAPERLESS_ALLOWED_HOSTS=<comma-separated-list>
 
     Can also be set using PAPERLESS_URL (see above).
 
+    If manually set, please remember to include "localhost". Otherwise docker
+    healthcheck will fail.
+
     Defaults to "*", which is all hosts.
 
 PAPERLESS_CORS_ALLOWED_HOSTS=<comma-separated-list>

src/paperless/settings.py

@@ -251,7 +251,8 @@ if _paperless_url:
     if _allowed_hosts:
         ALLOWED_HOSTS.append(_paperless_uri.hostname)
     else:
-        ALLOWED_HOSTS = [_paperless_uri.hostname]
+        # always allow localhost. Necessary e.g. for healthcheck in docker.
+        ALLOWED_HOSTS = [_paperless_uri.hostname] + ["localhost"]
 
 # The secret key has a default that should be fine so long as you're hosting
 # Paperless on a closed network.  However, if you're putting this anywhere