Merge r1862968, r1863191, r1867878, r1867882, r1867968, r1867971, r1869421, r1874491...

Merge r1862968, r1863191, r1867878, r1867882, r1867968, r1867971, r1869421, r1874491, r1874511, r1879119, r1879136, r1879860, r1881459, r1881559, r1867970 from trunk:

Add experimental support for fd passing in mod_cgid.  Attaches CGI
script stderr to the error log specific to the vhost, by passing the
appropriate fd over the AF_UNIX socket from the request handling
thread to the cgid server process.

* modules/generators/config5.m4: Add --enable-cgid-fdpassing.

* modules/generators/mod_cgid.c (sock_readhdr): New function, also
  returns auxiliary control data (the stderr fd) if available.
  (sock_write): Take optional aux fd argument, send it as control
  data.  (send_req, get_req): Adjust accordingly to pass/receive the
  stderr fd.
  (cgid_server): Use passed fd if available, limit the lifetime.

PR: 60692

mod_cgid: Continuation of r1862968, experimental fd passing support.

Split out CGI bucket implementation from mod_cgi and use in both
mod_cgi and mod_cgid, bringing stderr handling in mod_cgid up to par
with mod_cgi.  (There is a lot of code which has been copied between
mod_cgi{,d} so there's scope for further reduction of source
duplication between the modules using this header)

* modules/generators/cgi_common.h: Copied from mod_cgi.c, removed
  everything but the CGI bucket implementation with only one change:
  (struct cgi_bucket_data, cgi_bucket_create, cgi_bucket_read): Take a
  timeout on bucket creation, store and use on reads.

* modules/generators/mod_cgi.c [APR_FILES_AS_SOCKETS]: Include
  cgi_common.h.
  (cgi_handler): Pass configured timeout to CGI bucket.

* modules/generators/mod_cgid.c: Include cgi_common.h.
  (log_script_err): Copy from mod_cgi.c.
  (log_script): Use log_script_err.
  (send_req): Take fd for stderr.
  (cgid_child_errfn): Handle fd-passing case by writing error
  to stderr for client to pass through ap_log_rerror.
  (cgid_handler): Create pipe for stderr, pass write-end to
  server via send_req, use read-end to create CGI bucket.  Handle
  stderr output in failure paths.

PR: 54221

* modules/generators/mod_cgid.c (sock_readhdr): Only set up control
  message block when required; add some additional error handling.

* modules/generators/cgi_common.h (cgi_bucket_create):
  Disable APR timeout handling here for all callers.

* modules/generators/mod_cgi.c (cgi_handler): ... drop it here.

PR: 63797

Move common (and near-identical) code for CGI response output handling
to cgi_common.h; the diff between the modules for this code was as
follows:

https://people.apache.org/~jorton/mod_cgi-to-cgid-handler.diff

Change from previous: mod_cgi will now explicitly discard output when
returning HTTP_MOVED_TEMPORARILY for relative redirects (should not be
functionally different), TRACE1 logging of ap_pass_brigade failures
for mod_cgid is dropped.

* modules/generators/cgi_common.h (cgi_handle_response): New function,
  factored out from mod_cgid.
  (discard_script_output): Copied function from mod_cgi/d unchanged.

* modules/generator/mod_cgid.c (cgid_handler),
  modules/generator/mod_cgi.c (cgi_handler): Use cgi_handle_response.

Fix build broken w/o --enable-cgid-fdpassing by r1867968:

* modules/generators/cgi_common.h: Only define CGI bucket type
  if WANT_CGI_BUCKET is defined.

* modules/generators/mod_cgi.c: Always include cgi_common.h, defining
  WANT_CGI_BUCKET iff APR_FILES_AS_SOCKETS is defined

* modules/generators/mod_cgid.c: Always include cgi_common.h, defining
  WANT_CGI_BUCKET iff HAVE_CGID_FDPASSING (--enable-cgid-fdpassing).

Add comment, no functional change.

* modules/generators/cgi_common.h (cgi_handle_request): Factor out
  near-identical common code from mod_cgid, mod_cgi.

* modules/generators/mod_cgid.c (cgid_handler),
  modules/generators/mod_cgi.c (cgi_handler):
  Adjust to use cgi_handle_request.

* modules/generators/cgi_common.h (cgi_handle_request): Catch
  (unlikely) apr_bucket_read() failure when reading request.

* modules/generators/mod_cgid.c (cgid_handler): Bail immediately with
  a 503 response on errors when talking to the daemon.  Check the pid
  returned is not zero.

* modules/generators/mod_cgid.c (get_req): Add basic sanity
  checking for the structure received in the CGI daemon.

* modules/generators/mod_cgid.c (get_cgi_pid): Fix test for pid=0.
  (cgid_handler): Remove duplicated test for pid=0 here added in
  r1879119.

* modules/generators/cgi_common.h (cgi_handle_response): Avoid trying
  to read the output brigade twice in the case of a timeout.

PR: 64709

Further re-unification of code duplicated across mod_cgi/mod_cgid into
cgi_common.h.  Functional changes:

- brings the PR 61980 fix to mod_cgid as well, and
- some mod_cgid-specific APLOGNOs are dropped in favour of the
  code used in the equivalent error path in mod_cgi

... otherwise no user-visible changes (intended).

* modules/generators/cgi_common.h (log_scripterror, log_script_err): Move
  here from mod_cgi.
  (cgi_handle_exec): Move here, renamed from mod_cgi's handle_exec.
  (cgi_optfns_retrieve): New function, split out from mod_cgi's cgi_post_config.

* modules/generators/mod_cgid.c: Adjust accordingly, update to pass
  logno separately.
  (register_hooks): Register cgi_optfns_retrieve.

* modules/generators/mod_cgi.c: Adjust accordingly.
  (register_hooks): Register cgi_optfns_retrieve.

* modules/generators/cgi_common.h (discard_script_output): Simplify
  slightly and ensure constant rather than unlimited memory
  consumption when discarding CGI script output (for e.g. a redirect
  response).

Github: closes #209
Reviewed by: jorton, ylavic, covener

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1918379 13f79535-47bb-0310-9956-ffa450edef68