fix: ignore legacy publicConfig stream in createExternalExtensionProvider

CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed
+
+- Ignore legacy `publicConfig` stream in `createExternalExtensionProvider` to prevent `ObjectMultiplex - orphaned data for stream "publicConfig"` warnings ([#429](https://github.com/MetaMask/providers/pull/429))
+
 ## [22.1.1]
 
 ### Changed

src/extension-provider/createExternalExtensionProvider.test.ts

@@ -157,6 +157,23 @@ describe('createExternalExtensionProvider', () => {
     expect(global.chrome.runtime.connect).toHaveBeenCalledWith('foobar');
   });
 
+  it('ignores messages for the legacy publicConfig stream', async () => {
+    const consoleWarnSpy = jest.spyOn(globalThis.console, 'warn');
+    const { port } = await getInitializedProvider();
+
+    port.notify('publicConfig', {
+      jsonrpc: '2.0',
+      method: 'metamask_chainChanged',
+      params: { chainId: '0x1', networkVersion: '1' },
+    });
+    // Wait for the message to propagate through the stream pipeline.
+    await new Promise((resolve) => setTimeout(resolve, 10));
+
+    expect(consoleWarnSpy).not.toHaveBeenCalledWith(
+      'ObjectMultiplex - orphaned data for stream "publicConfig"',
+    );
+  });
+
   describe('RPC warnings', () => {
     const warnings = [
       {

src/extension-provider/createExternalExtensionProvider.ts

@@ -11,6 +11,12 @@ import { getDefaultExternalMiddleware } from '../utils';
 
 const browser = detect();
 
+/**
+ * The name of the legacy public config substream. The MetaMask extension
+ * still writes to this stream, but the provider no longer uses it.
+ */
+const LegacyPublicConfigStreamName = 'publicConfig';
+
 export type ExtensionType = 'stable' | 'flask' | 'beta' | string;
 
 /**
@@ -32,6 +38,10 @@ export function createExternalExtensionProvider(
     const pluginStream = new PortStream(metamaskPort);
     const streamName = MetaMaskInpageProviderStreamName;
     const mux = new ObjectMultiplex();
+    // The wallet still writes to the legacy `publicConfig` stream. Ignore it
+    // to avoid "ObjectMultiplex - orphaned data" warnings, mirroring how the
+    // MetaMask extension contentscript ignores legacy streams.
+    mux.ignoreStream(LegacyPublicConfigStreamName);
     pipeline(pluginStream, mux, pluginStream, (error: Error | null) => {
       let warningMsg = `Lost connection to "${streamName}".`;
       if (error?.stack) {