Extensions to give plugins a chance to set specific content-headers.

Added Distribution.content_headers_for() and call it from inside
Handler.response_headers().

This is in support of pulp/pulp_rpm#2947

closes pulp#3897.

CHANGES/plugin_api/3897.feature

@@ -0,0 +1,5 @@
+Added Distribution.content_headers_for() to let plugins affect content-app response headers.
+
+This can be useful, for example, when it's desirable for specific files to
+be served with Cache-control: no-cache.
+

pulpcore/app/models/publication.py

@@ -574,6 +574,17 @@ def content_handler_list_directory(self, rel_path):
         """
         return set()
 
+    def content_headers_for(self, path):
+        """
+        Opportunity for Distribution to specify response-headers for a specific path
+
+        Args:
+            path (str): The path being requested
+        Returns:
+            Empty dictionary, or a dictionary with HTTP Response header/value pairs.
+        """
+        return {}
+
     @hook(BEFORE_DELETE)
     @hook(
         AFTER_UPDATE,

pulpcore/content/handler.py

@@ -344,20 +344,27 @@ def _permit(request, distribution):
         return True
 
     @staticmethod
-    def response_headers(path):
+    def response_headers(path, distribution=None):
         """
         Get the Content-Type and Encoding-Type headers for the requested `path`.
 
         Args:
             path (str): The relative path that was requested.
-
+            distribution(Distribution) : Distribution detail that might want to add headers for path
         Returns:
             headers (dict): A dictionary of response headers.
         """
-        content_type = mime_types.get_type(path)
         headers = {}
-        if content_type:
+        if distribution:
+            headers.update(distribution.content_headers_for(path))
+
+        # If dist didn't hand us a content-type, determine from mime_types and set.
+        content_type = mime_types.get_type(path)
+        if content_type and not "Content-Type".casefold() in (
+            key.casefold() for key in headers.keys()
+        ):
             headers["Content-Type"] = content_type
+
         return headers
 
     @staticmethod
@@ -536,7 +543,7 @@ async def _match_and_stream(self, path, request):
         if content_handler_result is not None:
             return content_handler_result
 
-        headers = self.response_headers(rel_path)
+        headers = self.response_headers(rel_path, distro)
 
         repository = distro.repository
         publication = distro.publication
@@ -568,7 +575,7 @@ async def _match_and_stream(self, path, request):
                     await publication.published_artifact.aget(relative_path=index_path)
 
                     rel_path = index_path
-                    headers = self.response_headers(rel_path)
+                    headers = self.response_headers(rel_path, distro)
                 except ObjectDoesNotExist:
                     dir_list, dates, sizes = await self.list_directory(None, publication, rel_path)
                     dir_list.update(