PyPI hosted repository does not send etag header

Seems like the response from Nexus when downloading a hosted PyPI artifact doesn't include an etag or expires header.  This prevents pip from caching the artifact.  I see Maven handles this better by synthesizing an etag on upload if none is set:  MavenFacetUtils.java

You can see here for how pip handles the caching, and why an etag or expires header is desirable.
 
The response looks like:
 
HTTP/1.1 200 OK

Date: Mon, 02 Oct 2017 16:49:10 GMT

Server: Nexus/3.5.0-02 (OSS)

X-Frame-Options: SAMEORIGIN

X-Content-Type-Options: nosniff

Last-Modified: Mon, 25 Sep 2017 22:13:17 GMT

Content-Type: application/zip

Content-Length: 51711