Substituting same value multiple times with nginx sub_filter

Edit: Reproducible example: https://github.com/searchingforlife/nginx-substitution

I am trying to add/inject arbitrary number of scripts to an HTML file/output. They all filter on the same value </body> to inject themselves.

nginx version: nginx/1.16.1

Imagine we have two conf files like so (simplified):

# script_one.conf

sub_filter "</body>" "<script src='/one.js'></script></body>";

# script_two.conf

sub_filter "</body>" "<script src='/two.js'></script></body>";

And our main nginx conf file:

location /one {
  sub_filter_once off;
  include /script_one.conf;
  include /script_two.conf;
}

This however does not seem to work and nginx only adds the first script. If the filter value is different (say one filters on </head> and the other on </body>), then nginx injects both scripts.

Is there a way to get around this limitation and have nginx inject both scripts? I know I can create a new conf file that combines both scripts into one and include that but that just doesn't scale when you have 10+ scripts to inject that can be combined in various ways depending on the location.

This is speculation, I haven't verified it from nginx source code. I assume nginx stores the keys to replace in a hash structure, that is, replace x with y.

Now, when nginx reads the configuration file in order, it first adds a key </body> to the replace map, and then replaces it with the second one.

I ended up thinking a different approach which only rewrites once. If anyone is interested, see the solution branch: https://github.com/searchingforlife/nginx-substitution/tree/solution

Basically, we create a variable that holds names of scripts to inject, and then inject them all at once. This way, we end up only rewriting once.

location ~ ^/ {
  set $js_args "one,two";
  include scripts.conf;
}

# scripts.conf

if ($js_args ~ "^$") {
  set $js_args '';
}

set $scripts "";

if ($js_args ~* "(,|^)one([,]|$)") {
  set $scripts "${scripts}<script src='/one.js'></script>";
}

if ($js_args ~* "(,|^)two([,]|$)") {
  set $scripts "${scripts}<script src='/two.js'></script>";
}

sub_filter "</body>" "${scripts}</body>";