Can not get response body in the body_filter on my custom plugin

[showcup]

Can not get response body in the body_filter on my custom plugin，The following code is in body_filter:

function _M.body_filter(conf,ctx)
    local final_body = core.response.hold_body_chunk(ctx)
    if not final_body then
        core.log.warn(' response body is nil')
        return
    end
    --final_body = transform(final_body)
    ngx.arg[1] = final_body
end

final_body is nil when it runs, I want to transform response , these codes refer to the response-rewrite plugin. In response-rewrite, response body can be modified through filters, but respone body cannot be obtained in my custom plugin please help me!

[showcup]

@tzssangglass I've noticed that you frequently appear in discussions. Could you take a look at my question?

[tokers]

Yes, the body filter can be run multiple times, as APISIX sends a response body in the stream way.

[showcup]

Yes, the body filter can be run multiple times, as APISIX sends a response body in the stream way.

So the response is nil, what is the problem？

[showcup]

@tokers 能帮忙看下问题出在哪里吗？

[tokers]

Which line is line 180? I can't capture it quickly.

[showcup]

Which line is line 180? I can't capture it quickly.

[tokers]

@showcup The purpose of the hold_body_chunk method is to hold the whole response body, so before it read all the body from the upstream, it will return nil. So such a warning message is normal and useless.