Major Description
These four configurations options where added to fix a real problem (content duplications in cache):
{RECT_CONFIG, "proxy.config.http.cache.ignore_accept_mismatch", RECD_INT, "0", RECU_DYNAMIC, RR_NULL, RECC_INT, "[0-1]", RECA_NULL}
,
{RECT_CONFIG, "proxy.config.http.cache.ignore_accept_language_mismatch", RECD_INT, "0", RECU_DYNAMIC, RR_NULL, RECC_INT, "[0-1]", RECA_NULL}
,
{RECT_CONFIG, "proxy.config.http.cache.ignore_accept_encoding_mismatch", RECD_INT, "0", RECU_DYNAMIC, RR_NULL, RECC_INT, "[0-1]", RECA_NULL}
,
{RECT_CONFIG, "proxy.config.http.cache.ignore_accept_charset_mismatch", RECD_INT, "0", RECU_DYNAMIC, RR_NULL, RECC_INT, "[0-1]", RECA_NULL}
,
However, as implemented, they are pretty much useless, and if enabled, have high risk of giving wrong content. To make things worse, they are global configurations, since they are not passable from the HTTPSM into the cache.
I've examine the code thoroughly, and I actually think these configurations had the right intentions, but just implemented it wrong. What they really ought to have been is e.g. proxy.config.http.cache.relax_accept_encoding_match .
What should happen (IMO) is that these four configs (ideally we'd rename them or make new ones) would check if there is no Vary: header in the cached entry. IF there is no Vary: header, AND one of these settings it set, we skip that matching that happens on the cache client header and the incoming client header entirely (give the match a score of 1.0). These configs should ideally also be per-remap overridable, but that requires code changes like TS-1919.
A real use case scenario is this: Assume a content is always served by origin without Content-Encoding, or Vary: header. This would be typical for e.g. a PNG (image).
Upon cache miss, if the first request comes with Accept-Encoding: gzip, everything is fine, and we serve this cached item to all clients thereafter. However, if the first request comes with no Accept-Encoding: header whatsoever, that response can not satisfy a response from a request with AE: gzip, so we get at least two copies of the same object in cache.
I'm curious to get some input on this, and let me know if the explanations makes no sense. 