API disabled in the context of body_filter_by_lua

[jensonzheng]

Hello, I would like to inquire why it is not possible to send HTTP requests using resty.http during the header_filter or body_filter phases.

Currently, there is a requirement to determine whether to retry a request based on the HTTP response status, and also to modify the original body and header information. I have tried retrying in the balance try_callback method, but it does not support modifying content by calling functions like kong.service.request.set_raw_body.

[chronolaw]

resty.http bases on ngx.tcp.socket, it only works in the phases which can yield. see https://github.com/openresty/lua-nginx-module?tab=readme-ov-file#ngxsockettcp.

[jensonzheng]

If requests cannot be sent during the header_filter or body_filter phase, what other methods can I try to resolve this issue, modify the message based on the result, and resend it?

I attempted to send the request using resty.http during the access phase and process the result myself. It works for non-streaming requests, but for streaming request responses, the result cannot be directly output using methods like ngx.print(). Do you have any suggestions?

[chronolaw]

I don't know the business context, but obviously header_filter/body_filter can not invoke any http request, perhaps we should change the thinking of the way.

[jensonzheng]

Thanks.
Additionally, I'd like to know if I send an SSE request during the access phase and obtain the streaming chunk results, how can I set it to kong to ensure that subsequent plugins can function properly? Is it by using the ngx.print(chunk) method, such as following codes:

function TestHandler:access(conf)
  kong.service.request.enable_buffering()
  ngx.header["Content-Type"] = "text/event-stream"
  ngx.status = "200"
  for i = 1, 30 do
    chunk = "data: " .. i .. "\n\n"
    ngx.print(chunk)
    -- kong.response.set_raw_body("hello world\n")  -- no work
    ngx.flush(true)
    ngx.sleep(1)
  end

  ngx.exit(200)
end

[chronolaw]

Store them in the ngx.ctx?

[jensonzheng]

i want to return them like sse protocol

[jensonzheng]

The issue I'm currently facing is this: when there's only one TestHandler plugin in the request, the mocked chunk content can be output one per second as coded. However, if I add another plugin before it, the response content becomes non-streaming and will be output entirely after 30 seconds.