flipper/docs/extending/create-plugin.mdx

---
id: create-plugin
title: Client Plugin API
---

import Tabs from '@theme/Tabs';
import TabItem from '@theme/TabItem';
import {FbInternalOnly, OssOnly} from 'internaldocs-fb-helpers';

## FlipperPlugin

The plugin implementation that runs on the (mobile) application side of things is called the _client plugin_ in Flipper terminology.
To build a client plugin, implement the `FlipperPlugin` interface.

The ID that is returned from your implementation needs to match the `name` defined in your JavaScript counterpart's `package.json`.


<Tabs defaultValue="android" values={[{label: 'Android', value: 'android'}, { label: 'iOS', value: 'ios'}, { label: 'C++', value: 'cpp'}, { label: 'React Native (JS)', value: 'rn' }, { label: 'React (JS)', value: 'js' }]}>
<TabItem value="android">

```java
public class MyFlipperPlugin implements FlipperPlugin {
  private FlipperConnection mConnection;

  @Override
  public String getId() {
    return "MyFlipperPlugin";
  }

  @Override
  public void onConnect(FlipperConnection connection) throws Exception {
    mConnection = connection;
  }

  @Override
  public void onDisconnect() throws Exception {
    mConnection = null;
  }

  @Override
  public boolean runInBackground() {
  	return false;
  }
}
```

</TabItem>
<TabItem value="ios">

```objc
@interface MyFlipperPlugin : NSObject<FlipperPlugin>
@end

@implementation MyFlipperPlugin

- (NSString*)identifier { return @"MyFlipperPlugin"; }
- (void)didConnect:(FlipperConnection*)connection {}
- (void)didDisconnect {}
- (BOOL)runInBackground {}

@end
```

</TabItem>
<TabItem value="cpp">

```cpp
class MyFlipperPlugin : public FlipperPlugin {
public:
  std::string identifier() const override { return "MyFlipperPlugin"; }
  void didConnect(std::shared_ptr<FlipperConnection> conn) override;
  void didDisconnect() override;
  bool runInBackground() override;
};
```

</TabItem>
<TabItem value="rn">

<div class="warning">

Please note that using Flipper from JavaScript in React Native requires the package [`react-native-flipper`](https://www.npmjs.com/package/react-native-flipper) to be installed in the hosting application.

</div>

```javascript
import {addPlugin} from 'react-native-flipper';

addPlugin({
  getId() {
    return 'MyFlipperPlugin';
  },
  onConnect(connection) {
    console.log('connected');
  },
  onDisconnect() {
    console.log('disconnected');
  },
  runInBackground() {
    return false;
  },
});
```
</TabItem>
<TabItem value="js">

<div class="warning">

Please note that using Flipper from JavaScript in your browser requires the package [`js-flipper`](https://www.npmjs.com/package/js-flipper) to be installed in the hosting application.

</div>

```javascript
import {flipperClient} from 'js-flipper';

// We want to import and start flipper client only in development and test modes
// We want to exclude it from our production build
let flipperClientPromise;
if (process.env.NODE_ENV !== 'production') {
  flipperClientPromise = import('js-flipper').then(({flipperClient}) => {
    flipperClient.start('React Tic-Tac-Toe');
    return flipperClient;
  });
}

flipperClientPromise?.then((flipperClient) => {
  flipperClient.addPlugin({
    getId() {
      return 'MyFlipperPlugin';
    },
    onConnect(connection) {
      console.log('connected');
    },
    onDisconnect() {
      console.log('disconnected');
    },
    runInBackground() {
      return false;
    },
  });
});
```
</TabItem>
</Tabs>


## Using FlipperConnection

`onConnect` will be called when your plugin becomes active. This will provide a `FlipperConnection` allowing you to register receivers for desktop method calls and respond with data.

<Tabs defaultValue="android" values={[{label: 'Android', value: 'android'}, { label: 'iOS', value: 'ios'}, { label: 'C++', value: 'cpp'}, { label: 'React Native (JS)', value: 'rn' }, { label: 'React (JS)', value: 'js' }]}>
<TabItem value="android">

```java
connection.receive("getData", new FlipperReceiver() {
  @Override
  public void onReceive(FlipperObject params, FlipperResponder responder) throws Exception {
    responder.success(
        new FlipperObject.Builder()
            .put("data", MyData.get())
            .build());
  }
});
```

</TabItem>
<TabItem value="ios">

```objc
@interface MyFlipperPlugin : NSObject<FlipperPlugin>
@end

@implementation MyFlipperPlugin

- (NSString*)identifier { return @"MyFlipperPlugin"; }

- (void)didConnect:(FlipperConnection*)connection
{
  [connection receive:@"getData" withBlock:^(NSDictionary *params, FlipperResponder *responder) {
    [responder success:@{
      @"data":[MyData get],
    }];
  }];
}

- (void)didDisonnect {}

@end
```

</TabItem>
<TabItem value="cpp">

```cpp
void MyFlipperPlugin::didConnect(std::shared_ptr<FlipperConnection> conn) {
  conn->receive("getData", [](const folly::dynamic &params,
                             std::unique_ptr<FlipperResponder> responder) {
    dynamic response = folly::dynamic::object("data", getMyData());
    responder->success(response);
  });
}
```

</TabItem>
<TabItem value="rn">

```javascript
addPlugin({
  getId() {
    return 'MyFlipperPlugin';
  },
  onConnect(connection) {
    console.log('connected');
    connection.receive('getData', (data, responder) => {
      console.log('incoming data', data);
      // respond with some data
      responder.success({
        ack: true,
      });
    });
  },
  // ...as-is
});
```

</TabItem>
<TabItem value="js">

```javascript
flipperClient.addPlugin({
  getId() {
    return 'MyFlipperPlugin';
  },
  onConnect(connection) {
    console.log('connected');
    connection.receive('getData', (data) => {
      console.log('incoming data', data);
      // return data to send it as a response
      return {
        ack: true,
      };
    });
    // Flipper client can also send the data you return from your async functions
    connection.receive('getDataAsync', async (data) => {
      console.log('incoming data', data);
      const myAsyncData = await doAsyncStuff();
      // return data to send it as a response
      return {
        data: myAsyncData,
      };
    });
    // Flipper client catches your exceptions and sends them as an error response to the desktop
    connection.receive('getErrorData', (data) => {
      console.log('incoming data', data);
      throw new Error('Ooops');
    });
    // It catches the execptions in your async functions as well
    connection.receive('getErrorDataAsync', async (data) => {
      console.log('incoming data', data);
      const myAsyncData = await doAsyncStuff();
      if (!myAsyncData) {
        throw new Error('Ooops! Async data is not there!!!');
      }
    });
  },
  // ...as-is
});
```

</TabItem>
</Tabs>

## Push data to the desktop

You don't have to wait for the desktop to request data though, you can also push data directly to the desktop. If the JS plugin subscribes to the same method, it will receive the data.

<Tabs defaultValue="android" values={[{label: 'Android', value: 'android'}, { label: 'iOS', value: 'ios'}, { label: 'C++', value: 'cpp'}, { label: 'React Native (JS)', value: 'rn' }, { label: 'React (JS)', value: 'js' }]}>
<TabItem value="android">

```java
connection.send("MyMessage",
    new FlipperObject.Builder()
        .put("message", "Hello")
        .build()
```

</TabItem>
<TabItem value="ios">

```objc
[connection send:@"getData" withParams:@{@"message":@"hello"}];
```

</TabItem>
<TabItem value="cpp">

```cpp
void MyFlipperPlugin::didConnect(std::shared_ptr<FlipperConnection> conn) {
  dynamic message = folly::dynamic::object("message", "hello");
  conn->send("getData", message);
}
```

</TabItem>
<TabItem value="rn">

```javascript
addPlugin({
  getId() {
    return 'MyFlipperPlugin';
  },
  onConnect(connection) {
    console.log('connected');
    connection.send('newRow', {message: 'Hello'});
  },
  // ...as-is
});
```

</TabItem>
<TabItem value="js">

```javascript
flipperClient.addPlugin({
  getId() {
    return 'MyFlipperPlugin';
  },
  onConnect(connection) {
    console.log('connected');
    connection.send('newRow', {message: 'Hello'});
  },
  // ...as-is
});
```

</TabItem>
</Tabs>

### Using a plugin instance to send data

It is often useful to get an instance of a Flipper plugin to send data to it. Flipper makes this simple with built-in support.

<FbInternalOnly>

#### Dependency Injection (Android only)

The preferred method to obtain a plugin instance is to use dependency injection when available.
For apps like fb4a that use dependency injection, a Module should have already been created by the create-plugin script.
This module will define a Singleton instance of your plugin that gets added to the FlipperClient.

You should use this instance of the plugin, by having it injected into your product code by the DI framework.
Alternatively, you can modify the plugin's injection module so that it injects a component into the FlipperPlugin.


</FbInternalOnly>

#### using FlipperClient to obtain a plugin instance

Plugins should be treated as singleton instances as there can only be one `FlipperClient` and each `FlipperClient` can only have one instance of a certain plugin. The Flipper API makes this simple by offering a way to get the current client and query it for plugins.

Plugins are identified by the string that their identifier method returns, in this example, "MyFlipperPlugin". Note that null checks may be required as plugins may not be initialized, for example in production builds.

<Tabs defaultValue="android" values={[{label: 'Android', value: 'android'}, { label: 'iOS', value: 'ios'}, { label: 'C++', value: 'cpp'}]}>
<TabItem value="android">

```java
final FlipperClient client = AndroidFlipperClient.getInstanceIfInitialized(context);
if (client != null) {
  final MyFlipperPlugin plugin = client.getPluginByClass(MyFlipperPlugin.class);
  plugin.sendData(myData);
}
```

</TabItem>
<TabItem value="ios">

```objc
FlipperClient *client = [FlipperClient sharedClient];
MyFlipperPlugin *myPlugin = [client pluginWithIdentifier:@"MyFlipperPlugin"];
[myPlugin sendData:myData];
```

</TabItem>
<TabItem value="cpp">

```cpp
auto& client = FlipperClient::instance();
auto myPlugin = client.getPlugin<MyFlipperPlugin>("MyFlipperPlugin");
if (myPlugin) {
  myPlugin->sendData(myData);
}
```
</TabItem>
</Tabs>


Here, `sendData` is an example of a method that might be implemented by the Flipper plugin.

### Bi-directional communication demo

An minimal communication demo for Android and iOS can be found in our Sample project:

* [Desktop implementation](https://github.com/facebook/flipper/blob/main/desktop/plugins/public/example/index.tsx)
* [Android](https://github.com/facebook/flipper/blob/main/android/sample/src/debug/java/com/facebook/flipper/plugins/example/ExampleFlipperPlugin.java) / [iOS](https://github.com/facebook/flipper/tree/7bd4f80c2570bebb52af3cf49e45fc6130d6a473/iOS/Plugins/FlipperKitExamplePlugin/FlipperKitExamplePlugin)

For React Native and JavaScript we have a simple game of Tic Tac Toe:

* [Desktop implementation](https://github.com/facebook/flipper/blob/main/desktop/plugins/public/rn-tic-tac-toe/index.tsx)
* [React Native implementation](https://github.com/facebook/flipper/tree/main/react-native/ReactNativeFlipperExample) / [JavaScript (React) implementation](https://github.com/facebook/flipper/tree/main/js/react-flipper-example)


## Background Plugins

In some cases you may want to provide data to Flipper even when your plugin is not currently active. Returning true in `runInBackground()` will result in `onConnect` being called as soon as Flipper connects, and allow you to use the connection at any time. See the [Client Plugin Lifecycle](client-plugin-lifecycle) for more details.

The benefit is that the desktop plugin can process this data in the background and fire notifications. It also reduces the number of renders and time taken to display the data when the plugin becomes active.

<div class="warning">

Please note that a background plugin could keep some data in memory until a Flipper connection is available, for example to keep statistics about the app startup process.
However, a plugin shouldn't assume it will eventually get a connection, since this depends on whether the user has enabled the plugin on the Desktop side.
So make sure to not store unbounded amounts of data!

</div>