How to reset post data properly

Question

I have this piece of code that I am calling within the loop to get image metadata ( title/caption and description ). It works fine but it only works for the first post in the loop. So I assume it needs to be reset. From looking here I think wp_rest_postdata(); is the right way to reset the query, but still the output fails for all but the first post, it repeats the data from the first post for every other post.

function get_image_metadata() {

    $image_id = get_post_thumbnail_id($post->ID);
    $args = array(
        'post_type' => 'attachment',
        'post_status' => null,
        'post_parent' => $post->ID,
        'include'  => $image_id
        ); 
    $image_data = get_posts($args);

    if ($image_data && isset($image_data[0])) {
        $meta_output['title'] = $image_data[0]->post_title; 
        $meta_output['caption'] =  $image_data[0]->post_excerpt; 
        $meta_output['description'] =  $image_data[0]->post_content; 
    }
    //wp_reset_query();
    wp_rest_postdata();
    return $meta_output;
}

Answer 1

When using get_posts() you don't actually setup post data unless you do so explicitly, via setup_postdata() inside your (usually a foreach) loop.

So, since you're not setting up post data, you shouldn't need to reset post data.

but still the output fails for all but the first post

I think that's because you're calling the global $post inside your function, but aren't globalizing it first:

$image_id = get_post_thumbnail_id($post->ID);
$args = array(
    'post_type' => 'attachment',
    'post_status' => null,
    'post_parent' => $post->ID,
    'include'  => $image_id
    ); 
$image_data = get_posts($args);

Try adding global $post; before using $post->ID:

global $post;
$image_id = get_post_thumbnail_id($post->ID);
$args = array(
    'post_type' => 'attachment',
    'post_status' => null,
    'post_parent' => $post->ID,
    'include'  => $image_id
    ); 
$image_data = get_posts($args);

If that's not the problem, can you clarify:

1. What data you get from $iamge_data
2. The context in which you are calling the function