WordPress at a glance
function is not described

wp_import_handle_upload() WP 2.0.0

Handle importer uploading and add attachment.

No Hooks.

Return

Array. Uploaded file's details on success, error message on failure

Usage

wp_import_handle_upload();

Changelog

Since 2.0.0 Introduced.

Code of wp import handle upload: wp-admin/includes/import.php WP 5.2.2

<?php
function wp_import_handle_upload() {
	if ( ! isset( $_FILES['import'] ) ) {
		return array(
			'error' => __( 'File is empty. Please upload something more substantial. This error could also be caused by uploads being disabled in your php.ini or by post_max_size being defined as smaller than upload_max_filesize in php.ini.' ),
		);
	}

	$overrides                 = array(
		'test_form' => false,
		'test_type' => false,
	);
	$_FILES['import']['name'] .= '.txt';
	$upload                    = wp_handle_upload( $_FILES['import'], $overrides );

	if ( isset( $upload['error'] ) ) {
		return $upload;
	}

	// Construct the object array
	$object = array(
		'post_title'     => wp_basename( $upload['file'] ),
		'post_content'   => $upload['url'],
		'post_mime_type' => $upload['type'],
		'guid'           => $upload['url'],
		'context'        => 'import',
		'post_status'    => 'private',
	);

	// Save the data
	$id = wp_insert_attachment( $object, $upload['file'] );

	/*
	 * Schedule a cleanup for one day from now in case of failed
	 * import or missing wp_import_cleanup() call.
	 */
	wp_schedule_single_event( time() + DAY_IN_SECONDS, 'importer_scheduled_cleanup', array( $id ) );

	return array(
		'file' => $upload['file'],
		'id'   => $id,
	);
}