feat: add getInitialURL and subscribe options to linking config

For apps with push notifications linking to screens inside the app, currently we need to handle them separately (e.g. [instructions for firebase](https://rnfirebase.io/messaging/notifications#handling-interaction), [instructions for expo notifications](https://docs.expo.io/push-notifications/receiving-notifications/)). But if we add a link in the notification to use for deep linking, we can instead reuse the same deep linking logic instead.

This commit adds the `getInitialURL` and `subscribe` options which internally used `Linking` API to allow more advanced implementations by combining it with other sources such as push notifications.

Example usage with Firebase notifications could look like this:

```js
const linking = {
  prefixes: ['myapp://', 'https://myapp.com'],
  async getInitialURL() {
    // Check if app was opened from a deep link
    const url = await Linking.getInitialURL();

    if (url != null) {
      return url;
    }

    // Check if there is an initial firebase notification
    const message = await messaging().getInitialNotification();

    // Get the `url` property from the notification which corresponds to a screen
    // This property needs to be set on the notification payload when sending it
    return message?.notification.url;
  },
  subscribe(listener) {
    const onReceiveURL = ({ url }: { url: string }) => listener(url);

    // Listen to incoming links from deep linking
    Linking.addEventListener('url', onReceiveURL);

    // Listen to firebase push notifications
    const unsubscribeNotification = messaging().onNotificationOpenedApp(
      (message) => {
        const url = message.notification.url;

        if (url) {
          // If the notification has a `url` property, use it for linking
          listener(url);
        }
      }
    );

    return () => {
      // Clean up the event listeners
      Linking.removeEventListener('url', onReceiveURL);
      unsubscribeNotification();
    };
  },
  config,
};
```

packages/native/src/types.tsx

@@ -49,6 +49,20 @@ export type LinkingOptions = {
    * ```
    */
   config?: { initialRouteName?: string; screens: PathConfigMap };
+  /**
+   * Custom function to get the initial URL used for linking.
+   * Uses `Linking.getInitialURL()` by default.
+   * Not supported on the web.
+   */
+  getInitialURL?: () => Promise<string | null | undefined>;
+  /**
+   * Custom function to get subscribe to URL updates.
+   * Uses `Linking.addEventListener('url', callback)` by default.
+   * Not supported on the web.
+   */
+  subscribe?: (
+    listener: (url: string) => void
+  ) => undefined | void | (() => void);
   /**
    * Custom function to parse the URL to a valid navigation state (advanced).
    * Only applicable on Web.

packages/native/src/useLinking.native.tsx

@@ -16,6 +16,22 @@ export default function useLinking(
     enabled = true,
     prefixes,
     config,
+    getInitialURL = () =>
+      Promise.race([
+        Linking.getInitialURL(),
+        new Promise<undefined>((resolve) =>
+          // Timeout in 150ms if `getInitialState` doesn't resolve
+          // Workaround for https://github.com/facebook/react-native/issues/25675
+          setTimeout(resolve, 150)
+        ),
+      ]),
+    subscribe = (listener) => {
+      const callback = ({ url }: { url: string }) => listener(url);
+
+      Linking.addEventListener('url', callback);
+
+      return () => Linking.removeEventListener('url', callback);
+    },
     getStateFromPath = getStateFromPathDefault,
   }: LinkingOptions
 ) {
@@ -48,14 +64,16 @@ export default function useLinking(
   const enabledRef = React.useRef(enabled);
   const prefixesRef = React.useRef(prefixes);
   const configRef = React.useRef(config);
+  const getInitialURLRef = React.useRef(getInitialURL);
   const getStateFromPathRef = React.useRef(getStateFromPath);
 
   React.useEffect(() => {
     enabledRef.current = enabled;
     prefixesRef.current = prefixes;
     configRef.current = config;
+    getInitialURLRef.current = getInitialURL;
     getStateFromPathRef.current = getStateFromPath;
-  }, [config, enabled, getStateFromPath, prefixes]);
+  }, [config, enabled, prefixes, getInitialURL, getStateFromPath]);
 
   const extractPathFromURL = React.useCallback((url: string) => {
     for (const prefix of prefixesRef.current) {
@@ -80,15 +98,7 @@ export default function useLinking(
       return undefined;
     }
 
-    const url = await (Promise.race([
-      Linking.getInitialURL(),
-      new Promise((resolve) =>
-        // Timeout in 150ms if `getInitialState` doesn't resolve
-        // Workaround for https://github.com/facebook/react-native/issues/25675
-        setTimeout(resolve, 150)
-      ),
-    ]) as Promise<string | null | undefined>);
-
+    const url = await getInitialURLRef.current();
     const path = url ? extractPathFromURL(url) : null;
 
     if (path) {
@@ -99,7 +109,7 @@ export default function useLinking(
   }, [extractPathFromURL]);
 
   React.useEffect(() => {
-    const listener = ({ url }: { url: string }) => {
+    const listener = (url: string) => {
       if (!enabled) {
         return;
       }
@@ -122,10 +132,8 @@ export default function useLinking(
       }
     };
 
-    Linking.addEventListener('url', listener);
-
-    return () => Linking.removeEventListener('url', listener);
-  }, [enabled, extractPathFromURL, ref]);
+    return subscribe(listener);
+  }, [enabled, ref, subscribe, extractPathFromURL]);
 
   return {
     getInitialState,