upload image with rest API to the media library

1. Does functions.php continuously execute while WordPress is running?

Yes, it’s run on each page load. You can learn more about the (theme) functions file at https://developer.wordpress.org/themes/basics/theme-functions/.

2. Should this be in functions.php file and how do i get it to execute only once?

It can be put in that file, however, it should be run conditionally, e.g. put it in a function and then call the function from within your template file, or from within a hook. That’s how you can get it to execute only once. (but whether it’s actually going to be executed only once, depends on your code)

Example:

• Code in the active theme’s functions.php file:

  <?php
  /**
   * Your Theme functions and definitions
   *
   * @link https://developer.wordpress.org/themes/basics/theme-functions/
   */
  
  function my_upload_image_function() {
      // your code here which uploads the image
  }
  

• Then in your template file, just call the function when necessary: my_upload_image_function().

• Or you can hook the function on a specific action:

  add_action( 'hook_name', 'my_upload_image_function' );
  

So that’s a brief info about the theme functions file, and now, this is about what your code is trying to do.

• I see you’re making a remote POST request to the /wp/v2/media endpoint, but actually, you could instead use rest_do_request to make API requests internally, or use a WordPress-specific function for uploading files like media_sideload_image() which fetches a remote image and adds it to the WordPress media library.