Upstream: fixed proxy_no_cache when caching errors. Caching errors, notably intercepted errors and internally generated 502/504 errors, as well as handling of cache revalidation with 304, did not take into account u->conf->no_cache predicates configured. As a result, an error might be cached even if configuration explicitly says not to. Fix is to check u->conf->no_cache in these cases. To simplify usage in multiple places, checking u->conf->no_cache is now done in a separate function. As a minor optimization, u->conf->no_cache is only checked if u->cacheable is set. As a side effect, this change also fixes caching errors after proxy_cache_bypass. Also, during cache revalidation u->cacheable is now tested, so 304 responses which disable caching won't extend cacheability of stored responses. Additionally, when caching internally generated 502/504 errors u->cacheable is now explicitly updated from u->headers_in.no_cache and u->headers_in.expired, restoring the behaviour before 8041:0784ab86ad08 (1.23.0) when an error happens while reading the response headers. Reported by Kirill A. Korinsky, https://freenginx.org/pipermail/nginx/2024-April/000082.html

# Copyright (C) Igor Sysoev
# Copyright (C) Nginx, Inc.


echo $ngx_n "checking for $ngx_include ...$ngx_c"

cat << END >> $NGX_AUTOCONF_ERR

----------------------------------------
checking for $ngx_include

END


ngx_found=no

cat << END > $NGX_AUTOTEST.c

$NGX_INCLUDE_SYS_PARAM_H
#include <$ngx_include>

int main(void) {
    return 0;
}

END


ngx_test="$CC -o $NGX_AUTOTEST $NGX_AUTOTEST.c"

eval "$ngx_test >> $NGX_AUTOCONF_ERR 2>&1"

if [ -x $NGX_AUTOTEST ]; then

    ngx_found=yes

    echo " found"

    ngx_name=`echo $ngx_include \
              | tr abcdefghijklmnopqrstuvwxyz/. ABCDEFGHIJKLMNOPQRSTUVWXYZ__`


    have=NGX_HAVE_$ngx_name . auto/have_headers

    eval "NGX_INCLUDE_$ngx_name='#include <$ngx_include>'"

else
    echo " not found"

    echo "----------"    >> $NGX_AUTOCONF_ERR
    cat $NGX_AUTOTEST.c  >> $NGX_AUTOCONF_ERR
    echo "----------"    >> $NGX_AUTOCONF_ERR
    echo $ngx_test       >> $NGX_AUTOCONF_ERR
    echo "----------"    >> $NGX_AUTOCONF_ERR
fi

rm -rf $NGX_AUTOTEST*