Introduce a middleware that allows for HttpResponses to be thrown from inner utility functions, to avoid boilerplate in views

entries/from_url.py

@@ -1,35 +1,35 @@
-from typing import Union
 from urllib.parse import urlparse
 
 from django.contrib.sites.models import Site
 from django.http import HttpResponse
 from django.urls import resolve, Resolver404
 from micropub.views import error
+from lemoncurry.middleware import ResponseException
 
 from .models import Entry
 
 
-def from_url(url: str) -> Union[Entry, HttpResponse]:
+def from_url(url: str) -> Entry:
     domain = Site.objects.get_current().domain
     if not url:
-        return error.bad_req('url parameter required')
+        raise ResponseException(error.bad_req('url parameter required'))
     if '//' not in url:
         url = '//' + url
     parts = urlparse(url, scheme='https')
     if parts.scheme not in ('http', 'https') or parts.netloc != domain:
-        return error.bad_req('url does not point to this site')
+        raise ResponseException(error.bad_req('url does not point to this site'))
 
     try:
         match = resolve(parts.path)
     except Resolver404:
-        return error.bad_req('url does not point to a valid page on this site')
+        raise ResponseException(error.bad_req('url does not point to a valid page on this site'))
 
     if match.view_name != 'entries:entry':
-        return error.bad_req('url does not point to an entry on this site')
+        raise ResponseException(error.bad_req('url does not point to an entry on this site'))
 
     try:
         entry = Entry.objects.get(pk=match.kwargs['id'])
     except Entry.DoesNotExist:
-        return error.bad_req('url does not point to an existing entry')
+        raise ResponseException(error.bad_req('url does not point to an existing entry'))
 
     return entry

lemoncurry/middleware.py

@@ -0,0 +1,14 @@
+from django.http import HttpRequest, HttpResponse
+from django.utils.deprecation import MiddlewareMixin
+
+
+class ResponseException(Exception):
+    def __init__(self, response: HttpResponse) -> None:
+        self.response = response
+
+
+class ResponseExceptionMiddleware(MiddlewareMixin):
+    def process_exception(self, request: HttpRequest, exception: Exception) -> HttpResponse:
+        if isinstance(exception, ResponseException):
+            return exception.response
+        raise exception

lemoncurry/settings/base.py

@@ -118,6 +118,7 @@ MIDDLEWARE = [
     'django.contrib.messages.middleware.MessageMiddleware',
     'django.contrib.sites.middleware.CurrentSiteMiddleware',
     'django.middleware.clickjacking.XFrameOptionsMiddleware',
+    'lemoncurry.middleware.ResponseExceptionMiddleware',
 ]
 
 ROOT_URLCONF = 'lemoncurry.urls'

micropub/views/delete.py

@@ -17,8 +17,6 @@ def delete(request):
         return error.unsupported_type(request.content_type)
     url = normalise[request.content_type](request)
     entry = from_url(url)
-    if isinstance(entry, HttpResponse):
-        return entry
 
     if entry.author != request.token.user:
         return error.forbid('entry belongs to another user')