Fix the use of the default 'flush' provider.
Improve documentation for the "flusher" parameter.
Remove useless empty lines.

See http://mail-archives.apache.org/mod_mbox/httpd-dev/200812.mbox/%3C494226C0.4050407@force-elite.com%3E for some more explanation.
A python script is given there to test.
I had to tweak it to have it work
(use:
        fd, payload = passfd.recvfd(conn.fileno())
instead of:
        fd = passfd.recvfd(conn.fileno())
)


This is a r1058621 regression, where somehow "char *flusher" has been turned into a "char flusher[]". So it is been broken since the beginning of 2.4.x

After this change (i.e. r1058621), 'flusher' is no more a pointer (NULL'ed when the structure it belongs to is created) but the address of an array within a structure. It can not be NULL anymore.
So, we now have to look at the content of the array itself to see if it has been initialized or if we have to use the default value instead.
Submitted by: jailletc36
Reviewed/backported by: jim


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For the "SSLStaplingReturnResponderErrors off" case, make sure to only
staple responses with certificate status "good". Also avoids including
inaccurate responses when the OCSP responder is not completely up
to date in terms of the CA-issued certificates (and provides interim
"unknown" or "extended revoked" [RFC 6960] status replies).

Log a certificate status other than "good" in stapling_check_response().

Propagate the "ok" status from stapling_check_response() back via both
stapling_renew_response() and get_and_check_cached_response() to the
callback code in stapling_cb(), enabling the decision whether to include
or skip the response.


insert missing LOGNO in ssl_util_stapling.c
Submitted by: kbrand
Reviewed/backported by: jim


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core: Limit to ten the number of tolerated empty lines between request,
and consume them before the pipelining check to avoid possible response
delay when reading the next request without flushing.

Before this commit, the maximum number of empty lines was the same as
configured LimitRequestFields, defaulting to 100, which was way too much.
We now use a fixed/hard limit of 10 (DEFAULT_LIMIT_BLANK_LINES).

check_pipeline() is changed to check for (up to the limit) and comsume the
trailing [CR]LFs so that they won't be interpreted as pipelined requests,
otherwise we would block on the next read without flushing data, and hence
possibly delay pending response(s) until the next/real request comes in or
the keepalive timeout expires.
 
Finally, when the maximum number of empty line is reached in
read_request_line(), or that request line does not contains at least a method
and an (valid) URI, we can fail early and avoid some failure detected in
further processing.


core: follow up to r1710095.
Simplify logic in check_pipeline(), and log unexpected errors.


core: follow up to r1710095, r1710105.
We can do this in a single (no inner) loop, and simplify again the logic.

Submitted by: ylavic
Reviewed/backported by: jim


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follow-up r1715371 


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Merge r1708107, r1709587, r1709602, r1709995, r1710231, r1710419, r1710572, r1710583, r1715023 from trunk:

mod_ssl: performing protocol switch directly after ALPN selection, mod_http2: connection hook inits network filters to force TLS handshake, reads input only if H2Direct explicitly enabled, changes H2Direct default to off even for cleartext connections

new ap_is_allowed_protocol() for testing configured protocols, added H2Upgrade on/off directive, changed H2Direct default back to on when h2c is in Protocols

moved ssl handshake trigger from mod_http2 to new process_connection hook in mod_ssl

mod_ssl: check request-server for TLS settings compatible to handshake server, allow request if equal, renegotiation checks: remember last used cipher_suite for optimizations, deny any regnegotiation in presence of master connection

announce protocol choices on first request

fixing compilation issue for older platform

disabling protocol upgrades on slave connections

first request on master connection only reports more preferred protocols in Upgrade header

mod_ssl: follow up to r1709602.
Fix "HTTP spoken on HTTPS port" broken by the SSL handshake trigger moved to
process_connection hook (r1709602) along with H2Direct speculative read.

Submitted by: icing, ylavic
Reviewed/backported by: jim


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