Logging Subrequests body / uri using access_log

Versions:
lua-nginx-module: 0.10.15
nginx core: 1.16.0

Hello,

First of all congrats for this really nice module!

I'm trying to use the lua-module to generate a log file containing the full requests and responses with the body and headers.

I currently have the hereafter script, which basically set variables, those variables are afterward used in a nginx log_format directive and printed by access_log (taken from there https://www.hardill.me.uk/wordpress/2018/03/14/logging-requests-and-response-with-nginx/):

lua_need_request_body on; 
set $resp_body "";
body_filter_by_lua_block {
  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
}
set $req_header "";
set $resp_header "";
header_filter_by_lua_block {
  local h = ngx.req.get_headers()
  for k, v in pairs(h) do
      ngx.var.req_header =  ngx.var.req_header .. k .. ": " .. v .. "\n"
  end
  local rh = ngx.resp.get_headers()
  for k, v in pairs(rh) do
      ngx.var.resp_header = ngx.var.resp_header .. k .. ": " .. v .. "\n"
  end
}

This is working, however now i'd like to execute this script from a location which is called by a subrequest. We are not using lua for our subrequests, we have made our own module (which launches multiple subrequests and works fine). The problem i'm facing is that the above script will print the body of the response sent to the client and not the one from the subrequest.
I'm sure this lua script is called because multiple subrequests are made to this location and the header variables are concatenated each time (this is not what i want but it allowed me to see that the script is getting called for each subrequest).

Here is the nginx location where i define this script:

location ~/mylocation/([^/]*)/(.*) {
   internal;
   proxy_set_header Host $1;
   proxy_pass http://$1/$2$is_args$args;
   include log_requests.lua;
}

This is to be used only for debugging in case of emergency therefore i do not care of the performance of the script.

Thanks for your help !

Maël

Start by reading the included log_requests.lua configuration and the shown body_filter_by_lua_block and header_filter_by_lua_block handlers, then trace how they are invoked for the internal location's subrequests and how access_log receives their variables. Done means determining the supported behavior for logging each subrequest's body and URI separately.