Generators

cross.stream generators use Nushell expressions to create streams of data that are emitted as frames into the store.

Basic Usage

To create a generator, append a Nushell expression with the topic <topic>.spawn:

"tail -F http.log | lines" | .append log.spawn

The generator will:

• Execute the provided Nushell expression
• Each line written to http.log will be emitted as a frame with topic log.recv
• Automatically restarts if it exits

Lifecycle Events

Generators emit lifecycle events to track their state:

Event	Description
<topic>.start	Generator has started processing
<topic>.recv	Output value from the generator
<topic>.stop	Generator has stopped
<topic>.spawn.error	Error occurred while spawning generator

All events include source_id which is the ID of the generator instance.

Configuration Options

Option	Type	Default	Description
duplex	boolean	false	Enable sending input to the generator’s pipeline via <topic>.send

Bi-directional Communication

When duplex is enabled, you can send data into the generator’s input pipeline via <topic>.send frames:

# Create a websocket connection
"websocat wss://echo.websocket.org" | .append echo.spawn --meta {duplex: true}

# Send input to the websocket
"hello" | .append echo.send

When running this generator:

• Lines received from the websocket server are emitted as <topic>.recv frames
• Content from <topic>.send frames is sent to the websocket server

Error Handling

If a generator encounters an error during spawning a <topic>.spawn.error frame is emitted with:

• source_id: ID of the failed spawn attempt
• reason: Error message describing what went wrong