From c2b7fb29de07bfe4c46dc90c426c52fb38d27b12 Mon Sep 17 00:00:00 2001
From: Pavel Feldman <pavel.feldman@gmail.com>
Date: Wed, 14 May 2025 20:15:09 -0700
Subject: [PATCH] chore: start trace server (#427)

---
 src/program.ts    | 10 ++++++++++
 src/transport.ts  |  2 +-
 tests/sse.spec.ts |  8 ++++----
 3 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/src/program.ts b/src/program.ts
index 59fb566..1f49736 100644
--- a/src/program.ts
+++ b/src/program.ts
@@ -18,6 +18,8 @@ import { program } from 'commander';
 
 import { startHttpTransport, startStdioTransport } from './transport.js';
 import { resolveCLIConfig } from './config.js';
+// @ts-ignore
+import { startTraceViewerServer } from 'playwright-core/lib/server';
 
 import type { Connection } from './connection.js';
 import { packageJSON } from './context.js';
@@ -59,6 +61,14 @@ program
         startHttpTransport(config, +options.port, options.host, connectionList);
       else
         await startStdioTransport(config, connectionList);
+
+      if (config.saveTrace) {
+        const server = await startTraceViewerServer();
+        const urlPrefix = server.urlPrefix('human-readable');
+        const url = urlPrefix + '/trace/index.html?trace=' + config.browser.launchOptions.tracesDir + '/trace.json';
+        // eslint-disable-next-line no-console
+        console.error('\nTrace viewer listening on ' + url);
+      }
     });
 
 function setupExitWatchdog(connectionList: Connection[]) {
diff --git a/src/transport.ts b/src/transport.ts
index 2ab7f03..d75bbc4 100644
--- a/src/transport.ts
+++ b/src/transport.ts
@@ -140,6 +140,6 @@ export function startHttpTransport(config: FullConfig, port: number, hostname: s
       'If your client supports streamable HTTP, you can use the /mcp endpoint instead.',
     ].join('\n');
     // eslint-disable-next-line no-console
-    console.log(message);
+    console.error(message);
   });
 }
diff --git a/tests/sse.spec.ts b/tests/sse.spec.ts
index 6c02107..73a0a25 100644
--- a/tests/sse.spec.ts
+++ b/tests/sse.spec.ts
@@ -35,10 +35,10 @@ const test = baseTest.extend<{ serverEndpoint: string }>({
   serverEndpoint: async ({}, use) => {
     const cp = spawn('node', [path.join(path.dirname(__filename), '../cli.js'), '--port', '0'], { stdio: 'pipe' });
     try {
-      let stdout = '';
-      const url = await new Promise<string>(resolve => cp.stdout?.on('data', data => {
-        stdout += data.toString();
-        const match = stdout.match(/Listening on (http:\/\/.*)/);
+      let stderr = '';
+      const url = await new Promise<string>(resolve => cp.stderr?.on('data', data => {
+        stderr += data.toString();
+        const match = stderr.match(/Listening on (http:\/\/.*)/);
         if (match)
           resolve(match[1]);
       }));