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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Constify + save a few bytes in conf pool

Save a few bytes in conf pool when processing 'AllowOverrideList'.

The 'override_list' table is allocated from the cmd->pool, just as all strings from argv[].
So there is no need to duplicate them.

+ some minor style issues

Save a few bytes in conf pool
Submitted by: jailletc36
Reviewed/backported by: jim


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mod_ssl: forward EOR (only) brigades to the core_output_filter().

mod_ssl: don't FLUSH output (blocking) on read.
This defeats deferred write (and pipelining), eg. check_pipeline() is not
expecting the pipe to be flushed under it.
So let OpenSSL >= 0.9.8m issue the flush when necessary (earlier versions
are known to not handle all the cases, so we keep flushing with those).


mod_ssl: follow up to r1705823.
Oups, every #if needs a #endif...

mod_ssl: pass through metadata buckets untouched in ssl_io_filter_output(),
the core output filter needs them.

Proposed by: jorton


mod_ssl: follow up to r1705194, r1705823, r1705826 and r1705828.
Add CHANGES entry, and restore ap_process_request_after_handler()'s comment
as prior to r1705194 (the change makes no sense now).


mod_ssl: follow up to r1705823.
We still need to flush in the middle of a SSL/TLS handshake.


mod_ssl: follow up to r1705823.
Flush SSL/TLS handshake data when writing (instead of before reading),
and only when necessary (openssl < 0.9.8m or proxy/client side).


mod_ssl: follow up to r1707230: fix (inverted) logic for SSL_in_connect_init().

Submitted by: ylavic
Reviewed/backported by: jim


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merge of 1708107,1709587,1709602,1709995,1710231,1710419,1710572,1710583 from trunk, addition of master conn_rec*, minor bump of mmn

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alignment (SPARC64, PPC64).
Submitted by: ylavic
Reviewed by: jim, minfrin


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           fields as described in RFC7230. See OWS definition.
Submitted by: jailletc36
Reviewed by: ylavic, minfrin


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