A generated event bus: publish/subscribe as a gRPC service in sixteen languages

Most systems eventually grow an event bus, and most event buses arrive as a heavyweight broker plus a client library per language. grpc-over-datachannels takes the generator's route instead: define the bus once as a gRPC service — grpcdc.events.v1.EventBus — and generate the broker and clients in all sixteen languages from that one schema.

The whole API is two calls

Publish takes routing tags, an opaque payload (typically your own serialized event proto), and a publisher id, and returns a broker-assigned sequence number. Subscribe takes a containment filter and returns a stream of events. An event carries its tags, payload, the broker-global sequence (1-based, in publish order), publisher id, and the broker's wall-clock timestamp.

Tag-value filtering

Tags are typed values — string, int64, double, bool, or any enum carried by number so it survives peers that do not know the enum. A subscription filter is a list of (tag, value) pairs, and an event is delivered when its tag list contains every pair in the filter; an empty filter receives everything, and the same tag may appear several times when an event must carry several values. There is no query language to learn and no stringly-typed topic hierarchy to govern: matching is set containment, evaluated the same way in every generated implementation.

Why generated matters here

Because the bus is just a .proto, publishers and subscribers can be browser tabs, native services, or mixed pairs over a DataChannel, and the broker itself has a generated implementation per language — including a git-backed event log variant for durable, inspectable history. Sequence numbers make ordering claims testable, and the same generated BDD scenarios that grade the runtimes grade the bus. If your architecture needs events, you already have the client: it was generated with your other stubs.

Update (v0.35.12): the event bus now has a dedicated repository — browser-grpc/eventbus — with the schema, the full Python and JavaScript trees, generated sources for the other fourteen languages, and CI. Run the demo with docker run --rm ghcr.io/browser-grpc/eventbus-demo:latest.