SSI: fixed incorrect or duplicate stub output. Following 3518:eb3aaf8bd2a9 (0.8.37), r->request_output is only set if there are data in the first buffer sent in the subrequest. As a result, following the change mentioned this flag cannot be used to prevent duplicate ngx_http_ssi_stub_output() calls, since it is not set if there was already some output, but the first buffer was empty. Still, when there are multiple subrequests, even an empty subrequest response might be delayed by the postpone filter, leading to a second call of ngx_http_ssi_stub_output() during finalization from ngx_http_writer() the subreqest buffers are released by the postpone filter. Since r->request_output is not set after the first call, this resulted in duplicate stub output. Additionally, checking only the first buffer might be wrong in some unusual cases. For example, the first buffer might be empty if $r->flush() is called before printing any data in the embedded Perl module. Depending on the postpone_output value and corresponding sizes, this issue can result in either duplicate or unexpected stub output, or "zero size buf in writer" alerts. Following 8124:f5515e727656 (1.23.4), it became slightly easier to reproduce the issue, as empty static files and empty cache items now result in a response with an empty buffer. Before the change, an empty proxied response can be used to reproduce the issue. Fix is check all buffers and set r->request_output if any non-empty buffers are sent. This ensures that all unusual cases of non-empty responses are covered, and also that r->request_output will be set after the first stub output, preventing duplicate output. Reported by Jan Gassen.

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


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

cat << END >> $NGX_AUTOCONF_ERR

----------------------------------------
checking for $ngx_type

END

ngx_found=no

for ngx_try in $ngx_type $ngx_types
do

    cat << END > $NGX_AUTOTEST.c

#include <sys/types.h>
#include <signal.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <sys/resource.h>
#include <netinet/in.h>
$NGX_INCLUDE_INTTYPES_H

int main(void) {
    $ngx_try i = 0;
    return (int) i;
}

END

    ngx_test="$CC $CC_TEST_FLAGS $CC_AUX_FLAGS \
              -o $NGX_AUTOTEST $NGX_AUTOTEST.c $NGX_LD_OPT $ngx_feature_libs"

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

    if [ -x $NGX_AUTOTEST ]; then
        if [ $ngx_try = $ngx_type ]; then
            echo " found"
            ngx_found=yes
        else
            echo ", $ngx_try used"
            ngx_found=$ngx_try
        fi
    fi

    if [ $ngx_found = no ]; then
        if [ $ngx_try = $ngx_type ]; then
            echo $ngx_n " $ngx_try not found$ngx_c"
        else
            echo $ngx_n ", $ngx_try not found$ngx_c"
        fi

        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*

    if [ $ngx_found != no ]; then
        break
    fi
done

if [ $ngx_found = no ]; then
    echo
    echo "$0: error: can not define $ngx_type"

    exit 1
fi

if [ $ngx_found != yes ]; then
    echo "typedef $ngx_found  $ngx_type;"   >> $NGX_AUTO_CONFIG_H
fi