messaging

Messaging Example

This example demonstrates a component that subscribes to a channel and is invoked when messages are published.

Structure

• config.toml: Component configuration with a subscription property
• publish.sh: Publishes a message via composable publish

This example reuses the greeter component from the hello-world example.

Running the Example

Change into the examples/messaging directory.

Publish a name via publish.sh (it will build the greeter component if not already built):

./publish.sh Alice

Output:

... invocation complete component=greeter function=greet result="Hello, Alice!"

You can also run composable publish directly:

composable publish config.toml --channel names --body Bob

How It Works

1. Subscription: The subscription property on a component tells the runtime to create a channel and subscribe the component to it. When a message arrives, the runtime invokes the component's exported function with the message body as the argument.
2. Publishing: composable publish starts the runtime, publishes a single message to the named channel, waits for processing, and exits.

Note

At this time, the component must export exactly one function, but more configuration options will be available for subscriptions soon, including the target function.

Configuration

[component.greeter]
uri = "../hello-world/greeter/target/wasm32-unknown-unknown/release/greeter.wasm"
subscription = "names"