Implement silent push notifications via Expo for rounds and LN receive

[hsjoberg]

https://notifee.app/react-native/docs/overview

https://notifee.app/react-native/docs/events#background-events

We need to implement silent push notification support via Firebase and APM in order to handle round coordination.
This functionality can also be used to for Lightning BOLT11 receive.

Questions and concerns:

• Will we be able to re-use existing react hook code? These are dependent on components being mounted which would not be the case when you wake up the phone
• How do we actually coordinate a round? Bark and aspd is currently pretty limited in what we can do
• Is Notifee up to the task? Otherwise we can do this on the native side. We will then have to figure out how to talk with NitroArk

[hsjoberg]

Expo has support for push notifications
https://docs.expo.dev/push-notifications/push-notifications-setup/

There is also this service that can support Android-forks that do not support Firebase.
https://pushy.me/

[hsjoberg]

Development branch push

[hsjoberg]

https://docs.expo.dev/versions/latest/sdk/notifications/#headless-background-notifications

https://docs.expo.dev/push-notifications/what-you-need-to-know/#headless-background-notifications

[hsjoberg]

This code can trigger a silent push

console.log("Hello");

async function sendSilentPush(expoPushToken: string) {
  const message = {
    to: expoPushToken,
    data: { someData: "goes here" },
    _contentAvailable: true,   // <- enables silent / headless mode
    priority: "high",          // <- helps Android deliver quickly
  };

  const res = await fetch("https://exp.host/--/api/v2/push/send", {
    method: "POST",
    headers: {
      Accept: "application/json",
      "Content-Type": "application/json",
    },
    body: JSON.stringify(message),
  });

  console.log("status", res.status);
  console.log("expo-response", await res.json());
}

sendSilentPush("ExponentPushToken[<token>]");

[hsjoberg]

We should use this helper lib for our round coordinator server https://github.com/expo/expo-server-sdk-node