FormData Handling Nested Arrays Incorrectly in Rails 7.1.2

[makoto-atarashi]

Issue Overview

After upgrading Rails from version 7.0.6 to 7.1.2, FormData that is including nested array sent from frontend is being received differently on backend, causing processing troubles.

Steps to Reproduce

1. Use the following frontend JavaScript code, which was working correctly with Rails 7.0.6, to send data to backend.

let formData = new FormData();

formData.append("items[][foo]", "FOO");
formData.append("items[][bar]", "BAR");
formData.append("items[][baz]", "BAZ");
formData.append("items[][list][][a]", "A");
formData.append("items[][list][][b]", "B");

fetch("/api_url", {
  method: "POST",
  body: formData
})
  .then(response => response.json())
  .then(data => {
    console.log(data);
  })
  .catch(error => {
    console.error(error);
  });

2. Upgrade to Rails 7.1.2 and use the same frontend code to send data to the backend again.

Expected Behavior

Expecting the data to be received on Rails 7.1.2 as it was on Rails 7.0.6.

Actual Behavior

Data received on Rails 7.0.6 was in the following format:

Parameters: {"items"=>[{"foo"=>"FOO", "bar"=>"BAR", "baz"=>"BAZ", "list"=>[{"a"=>"A", "b"=>"B"}]}], "host"=>"example.com"}

However, on Rails 7.1.2, it has changed as follows, and params[:items][:list] is not received as an array as expected:

Parameters: {"items"=>[{"foo"=>"FOO", "bar"=>"BAR", "baz"=>"BAZ", "list[]a"=>"A", "list[]b"=>"B"}], "host"=>"example.com"}

Environment

Rails Version: 7.0.6 -> 7.1.2
Ruby version: ruby 3.2.2-p53
Front End: JavaScript, Fetch API

Specific Issue Points

On Rails 7.0.6, params[:items][:list] was correctly received as an array, but on Rails 7.1.2, params[:items][:list] is not received as an array as expected.

[fatkodima]

Same as (similar to) #49783 ?

[orhantoy]

I don't see a difference between 7.0.6 and 7.1.2 when using that exact JS frontend code with new vanilla Rails apps.
Do you have special middleware or callbacks in your controllers that could be doing something to the params?

[makoto-atarashi]

Thank you for your comment. After conducting further investigation, it seems that the root cause of this issue lies in the upgrade of the Rack middleware rather than in Rails itself. Considering this, I am inclined to withdraw this issue here, as it appears to be more relevant to the Rack middleware.

• Nested parameters parsing error in rack 3.0.8 rack/rack#2128

Would you agree with closing this issue given the context provided?
Your thoughts or any additional insights on this matter would be appreciated.

[orhantoy]

@makoto-atarashi That rack issue does not seem to apply to the issue you're having and I couldn't reproduce the params you're seeing logged regardless of the version of rack. Would you mind reproducing the issue with a small Rails app and sharing it here publicly?

[rails-bot]

This issue has been automatically closed because there has been no follow-up response from the original author. We currently don't have enough information in order to take action. Please reach out if you have any additional information that will help us move this issue forward.