Incorrect handling of "If-None-Match" and "If-Modified-Since" request header 
combination
----------------------------------------------------------------------------------------

                 Key: CXF-4231
                 URL: https://issues.apache.org/jira/browse/CXF-4231
             Project: CXF
          Issue Type: Bug
          Components: JAX-RS
    Affects Versions: 2.5
            Reporter: Jan Engehausen


I have a case where I set both a (weak) "ETag" and a "Last-Modified" response 
header. I noticed
that javax.ws.rs.core.Request.evaluatePreconditions(Date, EntityTag) 
unexpectedly returns a
response builder with status code 304 when the ETags differ but the last 
modified dates are
identical. This is because after the failing check against the ETag the current 
code simply performs
the check against the timestamp. According to RFC 2616, section 14.26 
(http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html):
"If none of the entity tags match, then the server MAY perform the requested 
method as if the If-None-Match header field did not exist, but MUST also ignore 
any If-Modified-Since header field(s) in the request. That is, if no entity 
tags match, then the server MUST NOT return a 304 (Not Modified) response."
This is currently not the case.
 
This code change works for my case, but some deeper thought needs to be given 
to possible
request header combinations (If-Match/If-None-Match and If-Modified-Since):
 
    public ResponseBuilder evaluatePreconditions(Date lastModified, EntityTag 
eTag) {
        final ResponseBuilder rb = evaluatePreconditions(eTag);
        if (rb != null) {
            // the ETag conditions match; so now conditions for last modified 
must match
            return evaluatePreconditions(lastModified);
        } else {
            // the ETag conditions do not match, so last modified should be 
ignored
            // see http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html 
(section 14.26 for
            // "If-None-Match", behavior not specified for "If-Match", section 
14.24)
            return null;
        }
    }
 
I assume that the most typical behavior for a browser is to send If-None-Match 
and If-Modified-Since,
and this case is currently not working.

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