Hi,

First of all, thanks @wtorsi for your time taking a look on this issue.

I have a similar issue when trying to POST arrays using the HttpClient component together with Mime. Let's say I am trying to send an array of tags for creating a media file.

$formFields = [
    'media' => [
        'tags' => [
            [
                'name' => 'first-tag'
            ],
            [
                'name' => 'first-tag'
            ]
        ],
    ],
];

Using the PR code, as result, I have the following field names:

name=media
name=media

However, when sending a form-data, what I expect on the backend is something like:

name=media[tags][0][name]
name=media[tags][1][name]

I changed a bit the closure function to have the result I was expecting, which I am not sure it is the correct way.

$prepare = function ($item, $key, $root = null) use (&$values, &$prepare) {
    $fieldName =  $root ? $root . '['.$key.']' : $key;

    if (\is_array($item)) {
        array_walk($item, $prepare, $fieldName);

        return;
    }

    $values[] = $this->preparePart($fieldName, $item);
};

Any thoughts?

Closing as it seems to have been fixed by #34032