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: A [subscription.<name>] block declares that a component should be subscribed to a channel. The channel field defaults to the subscription's name. When a message arrives on the channel, the runtime invokes the component's function with the message body as the argument. Optional fields: function (required when the component exports more than one), and the four mapping blocks - param-mapping, param-encoding, result-decoding, result-mapping - which apply in pipeline order to bridge the Message and the WIT call. See the mapping module docs for details.
2. Publishing: composable publish starts the runtime, publishes a single message to the named channel, waits for processing, and exits.

Configuration

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

[subscription.names]
component = "greeter"