Send data to external API after response is complete using WordPress shutdown - tweakswp.com tutorial

shutdown-external-api-after-response.php

<?php
/**
 * Sending data to an external API after the response is complete
 *
 * Uses fastcgi_finish_request() to flush output to the browser, then
 * fires the WordPress 'shutdown' action to POST data to an external
 * endpoint without blocking the user's page load.
 *
 * Tutorial: https://tweakswp.com/
 */

/**
 * Queue a payload to POST to an external API on shutdown.
 *
 * @param string $endpoint  Full URL of the external API endpoint.
 * @param array  $payload   Data to send as JSON.
 */
function tweakswp_send_after_response( string $endpoint, array $payload ): void {
    add_action(
        'shutdown',
        static function () use ( $endpoint, $payload ) {

            // Flush output to the browser if FastCGI is available.
            // After this call, the user's browser receives the complete response
            // and the connection is closed. PHP continues executing.
            if ( function_exists( 'fastcgi_finish_request' ) ) {
                fastcgi_finish_request();
            }

            // Do NOT use wp_remote_post() here — it respects WP_HTTP_BLOCK_EXTERNAL
            // and depends on hooks that may have already fired. Use a direct cURL call.
            $ch = curl_init( $endpoint );
            curl_setopt_array( $ch, [
                CURLOPT_POST           => true,
                CURLOPT_POSTFIELDS     => wp_json_encode( $payload ),
                CURLOPT_RETURNTRANSFER => true,
                CURLOPT_TIMEOUT        => 10,
                CURLOPT_HTTPHEADER     => [
                    'Content-Type: application/json',
                    'Accept: application/json',
                ],
            ] );
            $result = curl_exec( $ch );
            $status = curl_getinfo( $ch, CURLINFO_HTTP_CODE );
            curl_close( $ch );

            if ( WP_DEBUG ) {
                error_log( sprintf( '[shutdown API] %s → HTTP %d', $endpoint, $status ) );
            }
        },
        10
    );
}

// Usage example: send a conversion event after a WooCommerce order is placed.
add_action( 'woocommerce_thankyou', function ( int $order_id ) {
    $order = wc_get_order( $order_id );
    if ( ! $order ) {
        return;
    }

    tweakswp_send_after_response(
        'https://analytics.example.com/v1/events',
        [
            'event'      => 'purchase',
            'order_id'   => $order_id,
            'total'      => $order->get_total(),
            'currency'   => $order->get_currency(),
            'user_email' => $order->get_billing_email(),
        ]
    );
} );