How to log when response body length is less than 1k

[gaoxingliang]

I want to log the response body in file-logger and clickhouse-logger.
but I don't know how to limit the response body length.
I tried with below ideas:

1. register a trunked string in nginx conf.

 body_filter_by_lua 'local resp_body_trunc = string.sub(ngx.arg[1], 1, 1000);ngx.ctx.buffered = (ngx.ctx.buffered or "") .. resp_body_trunc;if ngx.arg[2] then;ngx.var.resp_body_trunc = ngx.ctx.buffered;end';

The original lua code is:

body_filter_by_lua '
        local resp_body = string.sub(ngx.arg[1], 1, 1000)
        ngx.ctx.buffered = (ngx.ctx.buffered or "") .. resp_body
        if ngx.arg[2] then
          ngx.var.resp_body = ngx.ctx.buffered
        end
        ';

but I don't know how to do that in apisix yaml config.

2. use the lua resty filter language:

below using a variable named body_bytes_sent. I don;t know what's the correct variable. some variables from here - https://apisix.apache.org/docs/apisix/plugins/file-logger/

{
    "path": "/usr/local/apisix/logs/apisix.log",
    "include_resp_body": true,
    "include_resp_body_expr":[
        [
            "body_bytes_sent",
            "<",
            1000
        ]
    ]

}

Any idea to NOT log the response body if it's too large？

[MekelCon]

Hello,

list of available variable are here :
http://nginx.org/en/docs/varindex.html

[tokers]

If your client doesn't use the chunked way to receive response body, you can check the response body size via the Content-Length header.

[gaoxingliang]

Hi @tokers , I'm using the chunked version. and I used the variable body_bytes_sent in the include_resp_body_expr
but it's not working.

[tokers]

body_bytes_sent is a variable you can know after the whole response body was sent, while in this logger plugin, the variable will be used in the body_filter phase; in such a case, the body is transmitting, and the total size is unknown. So it doesn't work.

[gaoxingliang]

So any idea to do this?

[tokers]

No way to do this if you use the chunk mechanism.

[gaoxingliang]

From this graph, in the log phase, it can get the total body length stuff:

Maybe we can get some workarounds?