Cosmo Streams adds three router handlers to enable subscription authorization, initial state delivery, and per-subscriber event filtering without building custom infrastructure.

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Cosmo Streams extends GraphQL subscriptions with three router-level handlers that enable subscription authorization, initial state delivery, and per-subscriber event filtering. The SubscriptionOnStart handler validates access and sends initial data when clients subscribe, OnReceiveEvent filters events per subscriber based on permissions, and OnPublishEvent validates mutation data before events enter the message broker. These handlers run as Go custom modules compiled into the router, eliminating the need for separate subscription services while providing fine-grained control over event-driven GraphQL subscriptions.

Three Handlers for Event Driven GraphQL Subscriptions

Problem 1: "You Can Subscribe to Everything or Nothing"

Problem 2: "New Subscribers See Nothing Until the Next Event"

Problem 3: "All Subscribers Get Identical Events"

The Mutation Side: OnPublishEvent Handler