Subscriptions

Use this when working in helios-subscriptions, the FHIR topic-based Subscriptions engine. It is consumed by helios-rest and helios-hfs. The engine evaluates resource events against SubscriptionTopic criteria and delivers notifications over channels.

Behavior

• Enable with HFS_SUBSCRIPTIONS_ENABLED=true.
• Channels: rest-hook (HTTP callback), websocket, email, and messaging.
• The messaging channel is separately gated by HFS_SUBSCRIPTION_MESSAGING_ENABLED.
• Endpoint safety: rest-hook delivery to private/loopback endpoints is blocked unless HFS_SUBSCRIPTION_ALLOW_PRIVATE_ENDPOINTS=true.
• Notification bundles follow the topic-based subscription spec; delivery failures retry with backoff (engine/retry.rs).
• WebSocket subscriptions use binding tokens (ws_token) managed per connection (ws_manager).

Channels (crates/subscriptions/src/channels/)

rest_hook, websocket (+ ws_manager, ws_token), email, messaging.

Environment

Variable	Description
HFS_SUBSCRIPTIONS_ENABLED	Master switch for the subscriptions engine
HFS_SUBSCRIPTION_MESSAGING_ENABLED	Enable the messaging channel
HFS_SUBSCRIPTION_ALLOW_PRIVATE_ENDPOINTS	Allow rest-hook delivery to private/loopback URLs (opt-in)
HFS_BASE_URL	Base URL used in notification links

Exact defaults are read in crates/rest/src/lib.rs and crates/subscriptions/src/config.rs.

Key API

SubscriptionEngine, SubscriptionConfig / MessagingSettings, ResourceEvent / ResourceEventType, WebSocketManager, WsBindingTokenManager, MessagingChannel, SubscriptionError.

Code map / tests

engine/ (+ retry), evaluator/ (filter_match), manager/ (filters, status), notification/ (builder, messaging), topics/, channels/, event.rs, config.rs. CI: .github/workflows/inferno-subscription.yml, subscriptions-channels.yml, subscriptions-smoke.yml. Unit tests inline in src/; integration tests under crates/subscriptions/tests/ where present.