From 59fb4845d6e49bca6b63cb12a617872682d3133a Mon Sep 17 00:00:00 2001
From: Xiaofu Huang <xiaofhua@microsoft.com>
Date: Tue, 6 May 2025 17:25:38 +0800
Subject: [PATCH 1/3] fix: Expose the MCP child process PID as an accessible
 property in StdioClientTransport

---
 src/client/stdio.ts | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/client/stdio.ts b/src/client/stdio.ts
index 9e35293d3..4f7f5f1b3 100644
--- a/src/client/stdio.ts
+++ b/src/client/stdio.ts
@@ -184,6 +184,10 @@ export class StdioClientTransport implements Transport {
     return this._process?.stderr ?? null;
   }
 
+  get pid(): number | undefined {
+    return this._process?.pid;
+  }
+
   private processReadBuffer() {
     while (true) {
       try {

From 7e134f259edbc0e0af897afc4c52154351e208d4 Mon Sep 17 00:00:00 2001
From: Xiaofu Huang <xiaofhua@microsoft.com>
Date: Tue, 6 May 2025 17:38:26 +0800
Subject: [PATCH 2/3] test: add ut of chile process pod in StdioClientTransport

---
 src/client/stdio.test.ts | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/src/client/stdio.test.ts b/src/client/stdio.test.ts
index 646f9ea5d..96dd5648d 100644
--- a/src/client/stdio.test.ts
+++ b/src/client/stdio.test.ts
@@ -59,3 +59,12 @@ test("should read messages", async () => {
 
   await client.close();
 });
+
+test("should return child process pid", async () => {
+  const client = new StdioClientTransport(serverParameters);
+
+  await client.start();
+  expect(client.pid).toBeDefined();
+  await client.close();
+  expect(client.pid).toBeUndefined();
+});

From d154914db74627bb70bbaf1842a9eb937e67a103 Mon Sep 17 00:00:00 2001
From: root <root@CPC-xiaof-9ATXB.>
Date: Tue, 6 May 2025 10:13:09 +0000
Subject: [PATCH 3/3] fix: change pid return type from undefined to be null

---
 src/client/stdio.test.ts | 4 ++--
 src/client/stdio.ts      | 9 +++++++--
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/src/client/stdio.test.ts b/src/client/stdio.test.ts
index 96dd5648d..b21324469 100644
--- a/src/client/stdio.test.ts
+++ b/src/client/stdio.test.ts
@@ -64,7 +64,7 @@ test("should return child process pid", async () => {
   const client = new StdioClientTransport(serverParameters);
 
   await client.start();
-  expect(client.pid).toBeDefined();
+  expect(client.pid).not.toBeNull();
   await client.close();
-  expect(client.pid).toBeUndefined();
+  expect(client.pid).toBeNull();
 });
diff --git a/src/client/stdio.ts b/src/client/stdio.ts
index 4f7f5f1b3..af29614ec 100644
--- a/src/client/stdio.ts
+++ b/src/client/stdio.ts
@@ -184,8 +184,13 @@ export class StdioClientTransport implements Transport {
     return this._process?.stderr ?? null;
   }
 
-  get pid(): number | undefined {
-    return this._process?.pid;
+  /**
+   * The child process pid spawned by this transport.
+   *
+   * This is only available after the transport has been started.
+   */
+  get pid(): number | null {
+    return this._process?.pid ?? null;
   }
 
   private processReadBuffer() {