Leif Hedstrom created TS-2245:
---------------------------------
Summary: Fix the semantics and behavior of e.g.
proxy.config.http.cache.ignore_accept_encoding_mismatch
Key: TS-2245
URL: https://issues.apache.org/jira/browse/TS-2245
Project: Traffic Server
Issue Type: Bug
Components: HTTP
Reporter: Leif Hedstrom
These four configurations options where added to fix a real problem (content
duplications in cache):
{code}
{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}
,
{code}
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. :)
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