Added unsubscribe return function to wsProvider.on() (#1780)

* Added unsubscribe return function to wsProvider.on()

* Updated mocks, added noop to http provider

packages/rpc-provider/src/http/index.ts

@@ -84,8 +84,11 @@ export default class HttpProvider implements ProviderInterface {
    * @description HTTP Provider does not have 'on' emitters. WebSockets should be used instead.
    */
   // eslint-disable-next-line @typescript-eslint/no-unused-vars
-  public on (type: ProviderInterfaceEmitted, sub: ProviderInterfaceEmitCb): void {
+  public on (type: ProviderInterfaceEmitted, sub: ProviderInterfaceEmitCb): () => void {
     l.error('HTTP Provider does not have \'on\' emitters, use WebSockets instead');
+    return (): void => {
+      // noop
+    };
   }
 
   /**

packages/rpc-provider/src/mock/index.ts

@@ -104,8 +104,11 @@ export default class Mock implements ProviderInterface {
     return true;
   }
 
-  public on (type: ProviderInterfaceEmitted, sub: ProviderInterfaceEmitCb): void {
+  public on (type: ProviderInterfaceEmitted, sub: ProviderInterfaceEmitCb): () => void {
     this.emitter.on(type, sub);
+    return (): void => {
+      this.emitter.removeListener(type, sub);
+    };
   }
 
   // eslint-disable-next-line @typescript-eslint/require-await

packages/rpc-provider/src/types.ts

@@ -47,7 +47,7 @@ export interface ProviderInterface {
   clone (): ProviderInterface;
   disconnect (): void;
   isConnected (): boolean;
-  on (type: ProviderInterfaceEmitted, sub: ProviderInterfaceEmitCb): void;
+  on (type: ProviderInterfaceEmitted, sub: ProviderInterfaceEmitCb): () => void;
   send (method: string, params: any[]): Promise<any>;
   subscribe (type: string, method: string, params: any[], cb: ProviderInterfaceCallback): Promise<number>;
   unsubscribe (type: string, method: string, id: number): Promise<boolean>;

packages/rpc-provider/src/ws/Provider.ts

@@ -167,9 +167,13 @@ export default class WsProvider implements WSProviderInterface {
    * @summary Listens on events after having subscribed using the [[subscribe]] function.
    * @param  {ProviderInterfaceEmitted} type Event
    * @param  {ProviderInterfaceEmitCb}  sub  Callback
+   * @return unsubscribe function
    */
-  public on (type: ProviderInterfaceEmitted, sub: ProviderInterfaceEmitCb): void {
+  public on (type: ProviderInterfaceEmitted, sub: ProviderInterfaceEmitCb): () => void {
     this._eventemitter.on(type, sub);
+    return (): void => {
+      this._eventemitter.removeListener(type, sub);
+    };
   }
 
   /**