Function hdk::api::emit_signal

pub fn emit_signal<S: Into<String>, J: Into<JsonString>>(
    name: S, 
    arguments: J
) -> ZomeApiResult<()>

Emits a signal that listeners can receive. (Status: MVP)

Part of Holochain's implementation of the Signal/Slot pattern. DNAs can define signals that various other modules can listen to / connect a slot with.

The main use-case of this is to provide a way to have callbacks of the UI get called so that UIs don't have to rely on polling in order to stay updated.

Currently, signals that are emitted with this function will be send over any websocket UI interface that includes an instance of this DNA. (In the future there might ways to connect signals of one instance with slots (i.e. zome functions) of other instances as a more abstract form of a bridge.)

A signal has a name and a set of arguments that are send with it. Currently (=MVP) both can be chosen arbitrarily and it is up to the hApp developer to make the assumptions in the UI match what is provided in the call to emit_signal() in the DNA. As we continue to implement the full ADR on signals (https://github.com/holochain/holochain-rust/blob/develop/doc/architecture/decisions/0013-signals-listeners-model-and-api.md), signals will have to be defined in the DNA so the conductor can check signal signatures when connecting them with slots.

Examples

pub fn handle_receive_chat_message(message: String) -> ZomeApiResult<()> {
    // ...
    hdk::emit_signal("message_received", JsonString::from_json(&format!(
        "{{message: {}}}", message
    )));
    // ...
    Ok(())
}