Better options would be:

1. Send partial HTTP response (206) with progress details which may be handled using AJAX progress API at the client before sending final response. This is processing and network intensive but may be needed in certain scenarios like drawing graphics etc. You cannot recover from connection loss.

2. Handover the task to a job scheduler and return the jobid. Client can then poll jobid using a status API or get the status pushed using a webhook. This is the more optimal approach for majority of cases.