osf: relay intended action to WB when asking for metadata

 * Add a header to the WB metadata request indicating if this is in
   service of a render or export action.

   The OSF would like to keep metrics on render and export requests.
   MFR does not talk to the OSF directly but does fetch metadata from
   WB, which verifies auth with the OSF.  MFR also downloads data from
   WB, but those requests will not be sent if MFR has cached the
   render/export output.  The only request guaranteed to run is the
   metadata request.  It's up to WB to interpret this and relay it to
   the OSF.

Author: felliott

mfr/providers/osf/provider.py

@@ -69,7 +69,11 @@ async def metadata(self):
         else:
             # URL is for WaterButler v1 API
             self.metrics.add('metadata.wb_api', 'v1')
-            metadata_response = await self._make_request('HEAD', download_url)
+            metadata_response = await self._make_request(
+                'HEAD',
+                download_url,
+                headers={settings.MFR_ACTION_HEADER: self.action or ''}
+            )
             response_code = metadata_response.status
             response_reason = metadata_response.reason
             response_headers = metadata_response.headers

mfr/providers/osf/settings.py

@@ -4,3 +4,4 @@
 config = settings.child('OSF_PROVIDER_CONFIG')
 
 MFR_IDENTIFYING_HEADER = config.get('MFR_IDENTIFYING_HEADER', 'X-Cos-Mfr-Render-Request')
+MFR_ACTION_HEADER = config.get('MFR_ACTION_HEADER', 'X-Cos-Mfr-Request-Action')