Expo background sync demo

demos/react-native-supabase-background-sync/.env.local.template

@@ -0,0 +1,4 @@
+# Replace the credentials below with your Supabase, PowerSync and Expo project details.
+EXPO_PUBLIC_SUPABASE_URL=https://foo.supabase.co
+EXPO_PUBLIC_SUPABASE_ANON_KEY=foo
+EXPO_PUBLIC_POWERSYNC_URL=https://foo.powersync.journeyapps.com

demos/react-native-supabase-background-sync/.gitignore

@@ -0,0 +1,47 @@
+# Learn more https://docs.github.com/en/get-started/getting-started-with-git/ignoring-files
+
+# dependencies
+node_modules/
+
+# Expo
+.expo/
+dist/
+web-build/
+
+# Native
+*.orig.*
+*.jks
+*.p8
+*.p12
+*.key
+*.mobileprovision
+
+# Metrom
+.metro-health-check*
+
+# debug
+npm-debug.*
+
+# macOS
+.DS_Store
+*.pem
+
+# local env files
+.env*.local
+.env
+
+# typescript
+*.tsbuildinfo
+
+# IDE
+.vscode
+.fleet
+.idea
+
+ios/
+
+# @generated expo-cli sync-2b81b286409207a5da26e14c78851eb30d8ccbdb
+# The following patterns were generated by expo-cli
+
+expo-env.d.ts
+# @end expo-cli

demos/react-native-supabase-background-sync/LICENSE

@@ -0,0 +1,121 @@
+Creative Commons Legal Code
+
+CC0 1.0 Universal
+
+    CREATIVE COMMONS CORPORATION IS NOT A LAW FIRM AND DOES NOT PROVIDE
+    LEGAL SERVICES. DISTRIBUTION OF THIS DOCUMENT DOES NOT CREATE AN
+    ATTORNEY-CLIENT RELATIONSHIP. CREATIVE COMMONS PROVIDES THIS
+    INFORMATION ON AN "AS-IS" BASIS. CREATIVE COMMONS MAKES NO WARRANTIES
+    REGARDING THE USE OF THIS DOCUMENT OR THE INFORMATION OR WORKS
+    PROVIDED HEREUNDER, AND DISCLAIMS LIABILITY FOR DAMAGES RESULTING FROM
+    THE USE OF THIS DOCUMENT OR THE INFORMATION OR WORKS PROVIDED
+    HEREUNDER.
+
+Statement of Purpose
+
+The laws of most jurisdictions throughout the world automatically confer
+exclusive Copyright and Related Rights (defined below) upon the creator
+and subsequent owner(s) (each and all, an "owner") of an original work of
+authorship and/or a database (each, a "Work").
+
+Certain owners wish to permanently relinquish those rights to a Work for
+the purpose of contributing to a commons of creative, cultural and
+scientific works ("Commons") that the public can reliably and without fear
+of later claims of infringement build upon, modify, incorporate in other
+works, reuse and redistribute as freely as possible in any form whatsoever
+and for any purposes, including without limitation commercial purposes.
+These owners may contribute to the Commons to promote the ideal of a free
+culture and the further production of creative, cultural and scientific
+works, or to gain reputation or greater distribution for their Work in
+part through the use and efforts of others.
+
+For these and/or other purposes and motivations, and without any
+expectation of additional consideration or compensation, the person
+associating CC0 with a Work (the "Affirmer"), to the extent that he or she
+is an owner of Copyright and Related Rights in the Work, voluntarily
+elects to apply CC0 to the Work and publicly distribute the Work under its
+terms, with knowledge of his or her Copyright and Related Rights in the
+Work and the meaning and intended legal effect of CC0 on those rights.
+
+1. Copyright and Related Rights. A Work made available under CC0 may be
+protected by copyright and related or neighboring rights ("Copyright and
+Related Rights"). Copyright and Related Rights include, but are not
+limited to, the following:
+
+  i. the right to reproduce, adapt, distribute, perform, display,
+     communicate, and translate a Work;
+ ii. moral rights retained by the original author(s) and/or performer(s);
+iii. publicity and privacy rights pertaining to a person's image or
+     likeness depicted in a Work;
+ iv. rights protecting against unfair competition in regards to a Work,
+     subject to the limitations in paragraph 4(a), below;
+  v. rights protecting the extraction, dissemination, use and reuse of data
+     in a Work;
+ vi. database rights (such as those arising under Directive 96/9/EC of the
+     European Parliament and of the Council of 11 March 1996 on the legal
+     protection of databases, and under any national implementation
+     thereof, including any amended or successor version of such
+     directive); and
+vii. other similar, equivalent or corresponding rights throughout the
+     world based on applicable law or treaty, and any national
+     implementations thereof.
+
+2. Waiver. To the greatest extent permitted by, but not in contravention
+of, applicable law, Affirmer hereby overtly, fully, permanently,
+irrevocably and unconditionally waives, abandons, and surrenders all of
+Affirmer's Copyright and Related Rights and associated claims and causes
+of action, whether now known or unknown (including existing as well as
+future claims and causes of action), in the Work (i) in all territories
+worldwide, (ii) for the maximum duration provided by applicable law or
+treaty (including future time extensions), (iii) in any current or future
+medium and for any number of copies, and (iv) for any purpose whatsoever,
+including without limitation commercial, advertising or promotional
+purposes (the "Waiver"). Affirmer makes the Waiver for the benefit of each
+member of the public at large and to the detriment of Affirmer's heirs and
+successors, fully intending that such Waiver shall not be subject to
+revocation, rescission, cancellation, termination, or any other legal or
+equitable action to disrupt the quiet enjoyment of the Work by the public
+as contemplated by Affirmer's express Statement of Purpose.
+
+3. Public License Fallback. Should any part of the Waiver for any reason
+be judged legally invalid or ineffective under applicable law, then the
+Waiver shall be preserved to the maximum extent permitted taking into
+account Affirmer's express Statement of Purpose. In addition, to the
+extent the Waiver is so judged Affirmer hereby grants to each affected
+person a royalty-free, non transferable, non sublicensable, non exclusive,
+irrevocable and unconditional license to exercise Affirmer's Copyright and
+Related Rights in the Work (i) in all territories worldwide, (ii) for the
+maximum duration provided by applicable law or treaty (including future
+time extensions), (iii) in any current or future medium and for any number
+of copies, and (iv) for any purpose whatsoever, including without
+limitation commercial, advertising or promotional purposes (the
+"License"). The License shall be deemed effective as of the date CC0 was
+applied by Affirmer to the Work. Should any part of the License for any
+reason be judged legally invalid or ineffective under applicable law, such
+partial invalidity or ineffectiveness shall not invalidate the remainder
+of the License, and in such case Affirmer hereby affirms that he or she
+will not (i) exercise any of his or her remaining Copyright and Related
+Rights in the Work or (ii) assert any associated claims and causes of
+action with respect to the Work, in either case contrary to Affirmer's
+express Statement of Purpose.
+
+4. Limitations and Disclaimers.
+
+ a. No trademark or patent rights held by Affirmer are waived, abandoned,
+    surrendered, licensed or otherwise affected by this document.
+ b. Affirmer offers the Work as-is and makes no representations or
+    warranties of any kind concerning the Work, express, implied,
+    statutory or otherwise, including without limitation warranties of
+    title, merchantability, fitness for a particular purpose, non
+    infringement, or the absence of latent or other defects, accuracy, or
+    the present or absence of errors, whether or not discoverable, all to
+    the greatest extent permissible under applicable law.
+ c. Affirmer disclaims responsibility for clearing rights of other persons
+    that may apply to the Work or any use thereof, including without
+    limitation any person's Copyright and Related Rights in the Work.
+    Further, Affirmer disclaims responsibility for obtaining any necessary
+    consents, permissions or other rights required for any use of the
+    Work.
+ d. Affirmer understands and acknowledges that Creative Commons is not a
+    party to this document and has no duty or obligation with respect to
+    this CC0 or use of the Work.

demos/react-native-supabase-background-sync/README.md

@@ -0,0 +1,173 @@
+# PowerSync + Supabase React Native Expo Background Sync
+
+## Overview
+
+Demo app demonstrating background sync using PowerSync, Expo and Supabase.
+
+This demo app uses expo-background-task to run a background task that syncs your PowerSync database in the background. To learn more, see the [Expo Background Task docs](https://docs.expo.dev/versions/latest/sdk/background-task).
+
+## Info
+
+The background sync logic is located in `library/utils.ts`.
+
+## Getting Started
+
+In the repo directory, use [pnpm](https://pnpm.io/installation) to install dependencies:
+
+```bash
+pnpm install
+pnpm build:packages
+```
+
+Then switch into the demo's directory:
+
+```bash
+cd demos/react-native-supabase-background-sync
+```
+
+Set up the Environment variables: Copy the `.env` file:
+
+```bash
+cp .env.local.template .env.local
+```
+
+And then edit `.env.local` to insert your credentials for `Supabase`.
+
+### Run on iOS (see [configuring background modes on iOS](https://docs.expo.dev/versions/latest/sdk/task-manager/#configuration))
+
+To enable background tasks in PowerSync on iOS, you need to add both processing and fetch to the UIBackgroundModes array in your app’s Info.plist (ios/powersyncreactnativebackgroundsync/Info.plist). The fetch mode is required so your app can periodically run background fetches, allowing PowerSync to upload and download data even when the app is not in the foreground:
+
+```xml
+<key>UIBackgroundModes</key>
+<array>
+    <string>processing</string>
+    <string>fetch</string>
+</array>
+```
+
+then run
+
+```sh
+pnpm ios
+```
+
+### Run on Android
+
+```sh
+pnpm android
+```
+
+## Supabase and background sync
+
+The `SupabaseConnector` has been configured to override the default `fetch` function that the `@supabase/supabase-js` SDK uses. By default, the `fetch` function used does not work in the background [see here](https://github.com/facebook/react-native/issues/47437), so we need to override it with a something that works in the background, like `expo/fetch`.
+
+```typescript
+this.client = createClient(AppConfig.supabaseUrl!, AppConfig.supabaseAnonKey!, {
+      auth: {
+        persistSession: true
+      },
+      global: {
+        // Override the default fetch function to use expo-fetch
+        fetch: fetch as any
+      }
+    });
+```
+
+## How to force a background task to run (in development)
+
+### Android
+
+`com.anonymous.powersyncreactnativebackgroundsync` is the package name of the app.
+
+The following command will show you the jobscheduler for your app:
+
+```bash
+adb shell dumpsys jobscheduler | grep -A 40 -m 1 -E "JOB #.* com.anonymous.powersyncreactnativebackgroundsync"
+```
+
+The result should look something like this:
+
+```bash
+JOB #u0a212/0: 74a550e com.anonymous.powersyncreactnativebackgroundsync/androidx.work.impl.background.systemjob.SystemJobService
+```
+
+The number after the `/` is the job ID. In this case, it is 0. You can use this to force the job to run by using the following command:
+
+```bash
+adb shell cmd jobscheduler run -f com.anonymous.powersyncreactnativebackgroundsync 0
+```
+
+### iOS
+
+Background tasks are not supported on iOS simulators.
+
+## ⚠️ Please note
+
+The app needs to be in the background for it to run and ultimately, the OS decides when to run background tasks so forcing it to run might not always work immediately. The background task should run on it's own within 20 minutes after the app is put in the background. Testing background sync seems to work better and more consistently on a physical device. If you don't see any logs after starting your background task, you may need to watch all the logs on the device using `adb logcat` (on Android).
+
+When the background task starts, you will see the following logs:
+
+```javascript
+[Background Task] Starting background task at ...
+[Background Task] Initializing PowerSync
+```
+
+After it has connected to the PowerSync instance, you will see the following log:
+
+```javascript
+[Background Task] Download complete
+Finished task 'background-powersync-task' with eventId ...
+```
+
+At this point, the background task has successfully connected to PowerSync (on a different thread) and inserted a mock list item to simulate pending transactions in the `ps_crud` table. It has not yet uploaded this transaction to the source database.
+
+After a couple of minutes, you will see the following logs:
+
+```javascript
+Could not apply checkpoint due to local data. Will retry at completed upload or next checkpoint.
+
+Could not apply pending checkpoint even after completed upload
+
+Validated and applied checkpoint
+```
+
+Typically this means that the background task has successfully uploaded the transaction to the source database.
+
+## The background task design
+
+This function `initializeBackgroundTask` sets up automatic background syncing for your app. Here's how it works:
+
+### What it does
+
+- Waits for your app to fully load before setting up background tasks
+- Watches for when users switch between your app and other apps
+- Registers the background task to run when the app goes to the background
+- Unregisters the background task when the app comes back to the foreground
+
+### Why this approach
+
+- Prevents conflicts - Avoids having multiple PowerSync connections (on different threads). When a task is unregistered, the connection to PowerSync is closed.
+
+### User experience
+
+- When user minimizes your app or switches to another app → background sync is scheduled to start
+- When user returns to your app → background sync stops if it is running (since the app can sync normally while in use)
+- User doesn't need to do anything - it's completely automatic
+
+### Technical details
+
+- Uses a minimum interval setting to control how often background sync runs (this is use-case dependent)
+- Checks if tasks are already registered to avoid duplicates
+- Includes logging to help with debugging
+
+This ensures your app stays up-to-date even when users aren't actively using it, while being efficient with device resources.
+
+### EAS Build configuration
+
+General information on defining environment variables with Expo can be [found here](https://docs.expo.dev/build-reference/variables/#can-eas-build-use-env-files).
+
+## Learn More
+
+Check out [the PowerSync SDK for React Native on GitHub](https://github.com/powersync-ja/powersync-js/tree/main/packages/react-native) - your feedback and contributions are welcome!
+
+To learn more about PowerSync, see the [PowerSync docs](https://docs.powersync.com).

demos/react-native-supabase-background-sync/android/.gitignore

@@ -0,0 +1,16 @@
+# OSX
+#
+.DS_Store
+
+# Android/IntelliJ
+#
+build/
+.idea
+.gradle
+local.properties
+*.iml
+*.hprof
+.cxx/
+
+# Bundle artifacts
+*.jsbundle