custom_fields_by_lua not handled properly by UI

[Nikhil VJ]

Hello, thank you so much to Konga's authors and contributors for making this amazing program.

I've found one potential frontend-side bug that might need just a simple tweak to fix, documenting it here.

Steps to replicate:

• Add "File log" plugin
• Try to pass a valid custom_fields_by_lua value in the custom_fields_by_lua field.

In the UI for File log plugin (I can't confirm if same issue is there for other plugins too which use the same field), the custom_fields_by_lua input doesn't accept any kind of input, even if it's valid in the actual plugin add/update api call to Kong.

This is a valid api call to Kong, made for updating a plugin on a service:

curl -X PATCH  http://localhost:8001/services/REDACTED/plugins/REDACTED \
  --header "Content-Type: application/json" \
  --data '{
    "name": "file-log",
    "config": {
      "path": "/data/log.log",
      "reopen": true,
      "custom_fields_by_lua": {
        "client_ip": "return nil",
        "route": "return nil"
      }
    }
  }'

But if I tried to put anything like the above json in the custom_fields_by_lua field in UI, I get an error response: "schema violation (config.custom_fields_by_lua: expected a map)"

Full CURL of the failed plugin update api call (with irrelevant parts removed / redacted):

curl 'http://REDACTED/kong/plugins/REDACTED' \
  -X 'PATCH' \
  -H 'Accept: application/json, text/plain, */*' \
  -H 'Content-Type: application/json;charset=UTF-8' \
  --data-raw '{"instance_name":null,"name":"file-log","consumer":null,"route":null,"tags":null,"updated_at":1686822097,"service":{"id":"REDACTED"},"protocols":["grpc","grpcs","http","https"],"id":"REDACTED","created_at":1686822097,"enabled":true,"config":{"path":"/data/log.log","reopen":true,"custom_fields_by_lua":"{ \"client_ip\": \"return nil\",  \"route\": \"return nil\" }"},"token":"REDACTED"}' 

Relevant parts of response:

{
  "statusCode": 400,
  "body": {
    "code": 2,
    "name": "schema violation",
    "fields": {
      "config": {
        "custom_fields_by_lua": "expected a map"
      }
    },
    "message": "schema violation (config.custom_fields_by_lua: expected a map)"
  }

Screenshot:

---

On the other hand, when there is an existing plugin having a proper custom_fields_by_lua configuration loaded, when the Konga GUI reads it, backend is sending the data properly, but GUI is failing to render the same.
Response of /plugins GET api is having:

"config": {
        "custom_fields_by_lua": {
          "request.headers.postman-token": "return nil",
          "authenticated_entity": "return nil",

proper. But UI is showing "[object Object]" in the form field. Screenshot:

My inference:

• backend is sending data correctly; frontend needs to stringify the custom_fields_by_lua json before populating in field
• when updating, frontend needs to parse the custom_fields_by_lua json value to JSON before sending, which presently it is sending stringified/quoted. Or, backend needs to parse the same into JSON before validating / proceeding to hit Kong api.

I have not run the source code of Konga to properly troubleshoot this - am just using the dockerized end product. Hoping someone can look into this and fix.

Thanks again for making this amazing program.