fix(logger): prevent meta_filter from caching access-phase verdict for log phase

[waterWang]

Description

Fixes #13724

Since 3.16.0, every logger plugin carries an access-phase handler (_M.access = log_util.check_and_read_req_body, introduced in #13034). Because the plugin now runs in access, run_plugin("access", ...) invokes meta_filter(), which evaluates the plugin's _meta.filter and caches the verdict for the rest of the request. This causes two problems:

A. Filter conditions on response-phase variables are decided before those variables have values.

A filter referencing $status or $upstream_status is evaluated against 0 / empty at access phase, and that wrong verdict is reused at log phase.

B. $status is cached as 0, corrupting the output of every plugin on the request.

status is not in no_cacheable_var_names, so the access-phase read of $status (which is 0 at access time) is cached into ctx.var for the remainder of the request. Every plugin that later reads $status gets 0.

Changes

apisix/plugin.lua

Include ngx.get_phase() in the meta_filter cache key so that access-phase and log-phase verdicts are cached separately. The log-phase call recomputes the verdict with correct response-phase variables.

apisix/core/ctx.lua

Add status to no_cacheable_var_names so that $status is never cached. Each read fetches from ngx.var.status directly, avoiding the access-phase 0 contamination.

Related

• This re-introduces the class of problem previously addressed in fix: meta.filter in plugin doesn't work in response-rewrite plugin #8162 / fix: APISIX extended variables cannot be used in _meta.filter #8256.