how to logging response body into access.log

[gracekk]

I try to use $resp_body in config.yml but failed.
Any ideas?
Or Can I use http-logger plugin write resp_body into file?

nginx_config:
http:
error_log_level: "info"
enable_access_log: true
access_log: logs/access.log
access_log_format: '{"@timestamp":"$time_iso8601","host":"$hostname","server_ip":"$server_addr","client_ip":"$remote_addr","xff":"$http_x_forwarded_for","domain":"$host","url":"$uri","referer":"$http_referer","args":"$args","upstreamtime":"$upstream_response_time","responsetime":"$request_time","request_method":"$request_method","status":"$status","size":"$body_bytes_sent","resp_body":"$resp_body","request_body":"$request_body","request_length":"$request_length","protocol":"$server_protocol","upstreamhost":"$upstream_addr","file_dir":"$uri","http_user_agent":"$http_user_agent"}'
access_log_format_escape: json
http_configuration_snippet: |
log_format my-custom-logs-format
'{"@timestamp":"$time_iso8601",'
'"host":"$hostname",'
'"server_ip":"$server_addr",'
'"client_ip":"$remote_addr",'
'"xff":"$http_x_forwarded_for",'
'"domain":"$host",'
'"url":"$uri",'
'"referer":"$http_referer",'
'"args":"$args",'
'"upstreamtime":"$upstream_response_time",'
'"responsetime":"$request_time",'
'"request_method":"$request_method",'
'"status":"$status",'
'"size":"$body_bytes_sent",'
'"request_body":"$request_body",'
'"request_length":"$request_length",'
'"protocol":"$server_protocol",'
'"upstreamhost":"$upstream_addr",'
'"file_dir":"$uri",'
'"resp_body:"$resp_body",'
'"http_user_agent":"$http_user_agent"'
'}';

[soulbird]

There is no built-in variable support to get the response body, if your response body size is unpredictable, I suggest you don't log it, it will make your log size very large.
But, If you insist on doing this, you can use the following way:
1、Set a var like:

set $resp_body '';

2、set log format:

access_log_format $resp_body;

3、Customize a plugin to assign a value to $resp_bdoy：

function _M.body_filter(conf, ctx)
    local body = core.response.hold_body_chunk(ctx)
    ctx.var.resp_body = body
    .............
end

[gracekk]

Thx for replay.
set $resp_body '' in this part?
http_server_configuration_snippet: |
set $resp_body '';

[juzn01]

request feature: can you add this as an plugin like proxy-mirror ???,some time my develop team need response from upstream via apisix before apisix send backto client.