Allow content_handler to return a content artifact

fixes #4635

CHANGES/plugin_api/4635.feature

@@ -0,0 +1,2 @@
+Added content app feature to accept a ``ContentArtifact`` from ``content_handler`` so that the
+plugin writer no longer has to generate a response when dealing with ``ContentArtifacts``.

docs/plugin_dev/api-reference/content-app.rst

@@ -17,7 +17,10 @@ Making a custom Handler is a two-step process:
 If content needs to be served from within the :term:`Distribution`'s base_path,
 overriding the :meth:`~pulpcore.plugin.models.Distribution.content_handler` and
 :meth:`~pulpcore.plugin.models.Distribution.content_handler_directory_listing`
-methods in your Distribution is an easier way to serve this content.
+methods in your Distribution is an easier way to serve this content. The
+:meth:`~pulpcore.plugin.models.Distribution.content_handler` method should
+return an instance of `aiohttp.web_response.Response` or a
+`pulpcore.plugin.models.ContentArtifact`.
 
 Creating your Handler
 ---------------------

pulpcore/content/handler.py

@@ -573,11 +573,22 @@ async def _match_and_stream(self, path, request):
         if not ends_in_slash:
             rel_path = f"{rel_path}/"
 
+        headers = self.response_headers(original_rel_path, distro)
+
         content_handler_result = await sync_to_async(distro.content_handler)(original_rel_path)
         if content_handler_result is not None:
-            return content_handler_result
-
-        headers = self.response_headers(original_rel_path, distro)
+            if isinstance(content_handler_result, ContentArtifact):
+                if content_handler_result.artifact:
+                    return await self._serve_content_artifact(
+                        content_handler_result, headers, request
+                    )
+                else:
+                    return await self._stream_content_artifact(
+                        request, StreamResponse(headers=headers), content_handler_result
+                    )
+            else:
+                # the result is a response so just return it
+                return content_handler_result
 
         repository = distro.repository
         publication = distro.publication