notifications-api/docs/message-sending-path.md

How messages are queued and sent

There are several ways for notifications to come into the API.

• Messages sent through the API enter through app/notifications/post_notifications.py
• One-off messages sent from the UI enter through create_one_off_notification in app/service/rest.py
• CSV uploads enter through app/job/rest.py

API messages and one-off UI messages come in one at a time, and take slightly-separate routes that both end up at persist_notification, which writes to the database, and provider_tasks.deliver_sms, which enqueues the sending.

For CSV uploads, the CSV is first stored in S3 and queued as a Job. When the job runs, it iterates through the rows, running process_job.save_sms to send notifications through persist_notification and provider_tasks.deliver_sms.