Example: Abstract Connection classes

packages/connect-multichain/src/multichain/connections/default-connection.ts

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+import type { Connection, ConnectionEvents, ConnectParams } from './types';
+import { type Scope, TransportType } from '../../domain';
+import { EventEmitter } from '../../domain/events';
+import { DefaultTransport } from '../transports/default';
+
+/**
+ * Strategy that talks to the in-page MetaMask provider (extension or in-app
+ * webview) over the standard `window.postMessage` transport.
+ *
+ * In contrast to MWP, this connection is also used in a "passive" mode while
+ * the SDK is idle so that the SDK can observe `wallet_sessionChanged` events
+ * emitted by the extension without an explicit user connect action.
+ */
+export class DefaultConnection
+  extends EventEmitter<ConnectionEvents>
+  implements Connection
+{
+  readonly type = TransportType.Browser;
+
+  readonly #transport: DefaultTransport;
+
+  #notificationUnsubscribe: (() => void) | undefined;
+
+  // eslint-disable-next-line no-restricted-syntax -- Constructors can't use hash names; factory is preferred
+  private constructor(transport: DefaultTransport) {
+    super();
+    this.#transport = transport;
+    this.#notificationUnsubscribe = transport.onNotification((data) => {
+      this.emit('notification', data);
+    });
+  }
+
+  /**
+   * Factory used by `MultichainClient` to construct a fresh connection.
+   *
+   * @returns A new `DefaultConnection` with a ready-to-use transport.
+   */
+  static create(): DefaultConnection {
+    return new DefaultConnection(new DefaultTransport());
+  }
+
+  get transport(): DefaultTransport {
+    return this.#transport;
+  }
+
+  isConnected(): boolean {
+    return this.#transport.isConnected();
+  }
+
+  /**
+   * Connect against the in-page MetaMask provider, opening or reusing a CAIP
+   * session as needed.
+   *
+   * @param params - Standard connect parameters.
+   */
+  async connect(params: ConnectParams): Promise<void> {
+    await this.#transport.connect(params);
+  }
+
+  /**
+   * Initialise the transport's message listener and emit an initial
+   * `wallet_sessionChanged` event without performing a `wallet_createSession`
+   * request. Used to keep a passive listener open when the SDK is idle.
+   *
+   * Mirrors the prior `MultichainClient` behaviour of catching init errors
+   * with `console.error('Passive init failed:', ...)`.
+   */
+  async initPassive(): Promise<void> {
+    try {
+      await this.#transport.init();
+    } catch (error) {
+      console.error('Passive init failed:', error);
+    }
+  }
+
+  async disconnect(scopes: Scope[] = []): Promise<void> {
+    await this.#transport.disconnect(scopes);
+  }
+
+  /**
+   * Releases the notification subscription. The DefaultTransport itself has
+   * no explicit teardown beyond this; the underlying `window` message
+   * listener is shared across `DefaultTransport` instances and is safe to
+   * leave in place.
+   */
+  async dispose(): Promise<void> {
+    this.#notificationUnsubscribe?.();
+    this.#notificationUnsubscribe = undefined;
+  }
+}

packages/connect-multichain/src/multichain/connections/index.ts

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+export { DefaultConnection } from './default-connection';
+export { MwpConnection } from './mwp-connection';
+export type {
+  Connection,
+  ConnectionContext,
+  ConnectionEvents,
+  ConnectParams,
+  MwpConnectFlow,
+  MwpConnectParams,
+} from './types';