fix: gracefully end sub-stream on port disconnect to prevent Premature close errors

Author: salimtb

shared/modules/caip-stream.test.ts

@@ -40,6 +40,18 @@ class MockStream extends Duplex {
   }
 }
 
+const createMockPort = () => {
+  // Minimal chrome.runtime.Port‐like stub
+  const listeners: (() => void)[] = [];
+  return {
+    onDisconnect: {
+      addListener: (fn: () => void) => listeners.push(fn),
+      // helper used by tests
+      _trigger: () => listeners.forEach((fn) => fn()),
+    },
+  };
+};
+
 describe('CAIP Stream', () => {
   describe('createCaipStream', () => {
     it('pipes and unwraps a caip-348 message from source stream to the substream', async () => {
@@ -92,5 +104,26 @@ describe('CAIP Stream', () => {
 
       await expect(promise).resolves.toBe(undefined);
     });
+
+    it('does not emit an error on “Premature close” after graceful shutdown', async () => {
+      const sourceStream = new MockStream();
+      const mockPort = createMockPort();
+      (sourceStream as unknown as { _port: typeof mockPort })._port = mockPort;
+
+      const providerStream = createCaipStream(sourceStream);
+
+      const errorSpy = jest.fn();
+      providerStream.on('error', errorSpy);
+
+      // Trigger disconnect
+      (
+        mockPort as unknown as { onDisconnect: { _trigger: () => void } }
+      ).onDisconnect._trigger();
+
+      // Give the event loop a tick to propagate potential errors
+      await new Promise((r) => setImmediate(r));
+
+      expect(errorSpy).not.toHaveBeenCalled();
+    });
   });
 });

shared/modules/caip-stream.ts

@@ -65,9 +65,38 @@ export class CaipStream extends Duplex {
 export const createCaipStream = (portStream: Duplex): Duplex => {
   const caipStream = new CaipStream();
 
-  pipeline(portStream, caipStream, portStream, (err: Error) => {
-    caipStream.substream.destroy();
-    console.log('MetaMask CAIP stream', err);
+  /** Cleanly end the CAIP side if the port goes away. */
+  const handlePortGone = () => {
+    // End only once
+    if (
+      !caipStream.substream.destroyed &&
+      !caipStream.substream.writableEnded
+    ) {
+      caipStream.substream.end();
+    }
+  };
+
+  /* ---------- 1. Listen for tab / iframe shutdown signals ---------- */
+
+  // a. Node-style streams emit 'close' and/or 'end'
+  portStream.once?.('close', handlePortGone);
+  portStream.once?.('end', handlePortGone);
+
+  // b. chrome.runtime.Port exposes onDisconnect
+  //    (ExtensionPortStream exposes the raw Port at `._port`)
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  const rawPort: chrome.runtime.Port | undefined = (portStream as any)?._port;
+  rawPort?.onDisconnect?.addListener(handlePortGone);
+
+  /* ---------- 2. Wire up the full duplex pipeline ---------- */
+
+  pipeline(portStream, caipStream, portStream, (err: Error | null) => {
+    caipStream.substream.destroy(); // full cleanup
+
+    // Ignore the normal premature-close that used to spam the console
+    if (err && err.message !== 'Premature close') {
+      console.error('MetaMask CAIP stream error:', err);
+    }
   });
 
   return caipStream.substream;