From 59fdd68c7c8ce2b214f5acd9f44a4038981f4419 Mon Sep 17 00:00:00 2001
From: Jacky Zhao <j.zhao2k19@gmail.com>
Date: Thu, 11 Dec 2025 17:21:30 -0800
Subject: [PATCH 1/2] catch construct error and re-report as protocol error

---
 transport/client.ts         | 18 ++++++++++-
 transport/transport.test.ts | 60 +++++++++++++++++++++++++++++++++++++
 2 files changed, 77 insertions(+), 1 deletion(-)

diff --git a/transport/client.ts b/transport/client.ts
index b9820e2e..5927e4f9 100644
--- a/transport/client.ts
+++ b/transport/client.ts
@@ -480,7 +480,23 @@ export abstract class ClientTransport<
     let metadata: unknown = undefined;
 
     if (this.handshakeExtensions) {
-      metadata = await this.handshakeExtensions.construct();
+      try {
+        metadata = await this.handshakeExtensions.construct();
+      } catch (err) {
+        const errStr = coerceErrorString(err);
+        this.log?.error(
+          `failed to construct handshake metadata for session to ${session.to}: ${errStr}`,
+          session.loggingMetadata,
+        );
+
+        this.protocolError({
+          type: ProtocolError.HandshakeFailed,
+          message: `failed to construct handshake metadata: ${errStr}`,
+        });
+        this.deleteSession(session, { unhealthy: true });
+
+        return;
+      }
     }
 
     // double-check to make sure we haven't transitioned the session yet
diff --git a/transport/transport.test.ts b/transport/transport.test.ts
index 9845da02..8c93f287 100644
--- a/transport/transport.test.ts
+++ b/transport/transport.test.ts
@@ -1590,6 +1590,66 @@ describe.each(testMatrix())(
       });
     });
 
+    test('construct throwing during handshake results in protocol error', async () => {
+      const schema = Type.Object({
+        foo: Type.String(),
+      });
+
+      interface Metadata {
+        foo: string;
+      }
+
+      const constructError = new Error('Failed to construct metadata');
+      const get = vi.fn(async () => {
+        throw constructError;
+      });
+      const parse = vi.fn(async (metadata: Metadata) => ({
+        foo: metadata.foo,
+      }));
+
+      const serverTransport = getServerTransport('SERVER', {
+        schema,
+        validate: parse,
+      });
+      const clientTransport = getClientTransport('client', {
+        schema,
+        construct: get,
+      });
+      const clientHandshakeFailed = vi.fn();
+      clientTransport.addEventListener('protocolError', clientHandshakeFailed);
+      clientTransport.connect(serverTransport.clientId);
+
+      addPostTestCleanup(async () => {
+        clientTransport.removeEventListener(
+          'protocolError',
+          clientHandshakeFailed,
+        );
+        await cleanupTransports([clientTransport, serverTransport]);
+      });
+
+      await waitFor(() => {
+        expect(get).toHaveBeenCalledTimes(1);
+        expect(clientHandshakeFailed).toHaveBeenCalledTimes(1);
+        expect(clientHandshakeFailed).toHaveBeenCalledWith(
+          expect.objectContaining({
+            type: ProtocolError.HandshakeFailed,
+            message:
+              'failed to construct handshake metadata: Failed to construct metadata',
+          }),
+        );
+        // should never get to the server
+        expect(parse).toHaveBeenCalledTimes(0);
+      });
+
+      expect(numberOfConnections(clientTransport)).toBe(0);
+      expect(numberOfConnections(serverTransport)).toBe(0);
+
+      await testFinishesCleanly({
+        clientTransports: [clientTransport],
+        serverTransport,
+      });
+    });
+
     test('server checks request schema on receive', async () => {
       const clientRequestSchema = Type.Object({
         foo: Type.Number(),

From 7e11a2967df7fb29f769c8b9e88af5d82e849947 Mon Sep 17 00:00:00 2001
From: Jacky Zhao <j.zhao2k19@gmail.com>
Date: Thu, 11 Dec 2025 17:22:45 -0800
Subject: [PATCH 2/2] 0.212.1

---
 package-lock.json | 4 ++--
 package.json      | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/package-lock.json b/package-lock.json
index 9c282b04..a2f98ccb 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "@replit/river",
-  "version": "0.212.0",
+  "version": "0.212.1",
   "lockfileVersion": 2,
   "requires": true,
   "packages": {
     "": {
       "name": "@replit/river",
-      "version": "0.212.0",
+      "version": "0.212.1",
       "license": "MIT",
       "dependencies": {
         "@msgpack/msgpack": "^3.1.2",
diff --git a/package.json b/package.json
index c12b48f6..0a85e9cf 100644
--- a/package.json
+++ b/package.json
@@ -1,7 +1,7 @@
 {
   "name": "@replit/river",
   "description": "It's like tRPC but... with JSON Schema Support, duplex streaming and support for service multiplexing. Transport agnostic!",
-  "version": "0.212.0",
+  "version": "0.212.1",
   "type": "module",
   "exports": {
     ".": {