♻️(backend) use additional http extra methods for content action

We used one drf extra action with both PATCH and GET https methods and
then split in two private methods and call them based on the http method
of the request. DRF allow to do this by using a mapping annotation
allowing us to have directly twi viewset actions used
django-rest-framework.org/api-guide/viewsets/#marking-extra-actions-for-routing

src/backend/core/api/viewsets.py

@@ -1850,8 +1850,11 @@ class DocumentViewSet(
 
         return drf.response.Response("authorized", headers=request.headers, status=200)
 
-    def _content_patch(self, request, document):
+    @drf.decorators.action(detail=True, methods=["patch"])
+    def content(self, request, *args, **kwargs):
         """Update the raw Yjs content of a document stored in S3."""
+        document = self.get_object()
+
         serializer = serializers.DocumentContentSerializer(data=request.data)
         serializer.is_valid(raise_exception=True)
 
@@ -1913,8 +1916,26 @@ class DocumentViewSet(
 
         return drf_response.Response(status=status.HTTP_204_NO_CONTENT)
 
-    def _content_retrieve(self, request, document):
-        """Retrieve the raw content file ni s3 and stream it."""
+    @content.mapping.get
+    def content_retrieve(self, request, *args, **kwargs):
+        """
+        Retrieve the raw content file from s3 and stream it.
+
+        We implement a HTTP cache based on the ETag and LastModified headers.
+        We retrieve the ETag and LastModified from the S3 head operation, save them in cache to
+        reuse them in future requests.
+        We check in the request if the ETag is present in the If-None-Match header and if it's the
+        same as the one from the S3 head operation, we return a 304 response.
+        If the ETag is not present or not the same, we do the same check based on the LastModifed
+        value if present in the If-Modified-Since header.
+        """
+        document = self.get_object()
+        # The S3 call to fetch the document can take time and the database
+        # connection is useless in this process. Hence we are closing it now
+        # to prevent having a massive number of database connections during
+        # the web-socket re-connection burst.
+        connection.close()
+
         if not (
             content_metadata := cache.get(
                 utils.get_content_metadata_cache_key(document.id)
@@ -1993,24 +2014,6 @@ class DocumentViewSet(
 
         return response
 
-    @drf.decorators.action(detail=True, methods=["patch", "get"], url_path="content")
-    def content(self, request, *args, **kwargs):
-        """Retrieve or update content stored in s3."""
-        document = self.get_object()
-
-        if request.method == "PATCH":
-            return self._content_patch(request, document)
-
-        if request.method == "GET":
-            # The S3 call to fetch the document can take time and the database
-            # connection is useless in this process. Hence we are closing it now
-            # to prevent having a massive number of database connections during
-            # the web-socket re-connection burst.
-            connection.close()
-            return self._content_retrieve(request, document)
-
-        return drf_response.Response(status=status.HTTP_501_NOT_IMPLEMENTED)
-
     @drf.decorators.action(detail=True, methods=["get"], url_path="media-check")
     def media_check(self, request, *args, **kwargs):
         """