Wikimedia Bugzilla is closed!

For ESI and some mobile use cases (first section retrieval) we need to be able to return just the body or even just the first section of the body from the cache. Range requests can be used to do this while sharing the same cache entry. To avoid a need for the client to know the ranges, we can set headers on our content that indicate those ranges. In Varnish, we can then simulate a range request internally with the offsets from those headers. This can be triggered with a special request header. ESI might indicate sub-requests in headers already. Mobile would need to set another header explicitly. 

Possible header:

Range: part=firstsection

(compare normal range requests with 'Range: bytes=1-5')