[lldb][mcp] Get the running MCP server connection information

[aperez]

Currently AFAICT we don't have a way to get the MCP server socket after it started. So this change introduces a new protocol-server subcommand that allows us to query the location of a running server:

(lldb) protocol-server start MCP listen://localhost:0
MCP server started with connection listeners: connection://[::1]:36051, connection://[127.0.0.1]:36051
(lldb) protocol-server get MCP
MCP server connection listeners: connection://[::1]:36051, connection://[127.0.0.1]:36051
(lldb) protocol-server stop MCP
(lldb) protocol-server get MCP
error: MCP server is not running

[llvmbot]

@llvm/pr-subscribers-lldb

Author: Alexandre Perez (aperez)

Changes

Currently AFAICT we don't have a way to get the MCP server socket after it started. So this change introduces a new protocol-server subcommand that allows us to query the location of a running server:

(lldb) protocol-server start MCP listen://localhost:0
MCP server started with connection listeners: connection://[::1]:36051, connection://[127.0.0.1]:36051
(lldb) protocol-server get MCP
MCP server connection listeners: connection://[::1]:36051, connection://[127.0.0.1]:36051
(lldb) protocol-server stop MCP
(lldb) protocol-server get MCP
error: MCP server is not running

---

Full diff: https://github.com/llvm/llvm-project/pull/162752.diff

3 Files Affected:

• (modified) lldb/source/Commands/CommandObjectProtocolServer.cpp (+44-1)
• (modified) lldb/source/Plugins/Protocol/MCP/ProtocolServerMCP.cpp (+1)
• (modified) lldb/test/API/commands/protocol/TestMCPUnixSocket.py (+13)

diff --git a/lldb/source/Commands/CommandObjectProtocolServer.cpp b/lldb/source/Commands/CommandObjectProtocolServer.cpp
index c5ab9e9f05bec..ff9d38c84ed2d 100644
--- a/lldb/source/Commands/CommandObjectProtocolServer.cpp
+++ b/lldb/source/Commands/CommandObjectProtocolServer.cpp
@@ -131,15 +131,58 @@ class CommandObjectProtocolServerStop : public CommandObjectParsed {
   }
 };
 
+class CommandObjectProtocolServerGet : public CommandObjectParsed {
+public:
+  CommandObjectProtocolServerGet(CommandInterpreter &interpreter)
+      : CommandObjectParsed(interpreter, "protocol-server get",
+                            "get protocol server connection information",
+                            "protocol-server get <protocol>") {
+    AddSimpleArgumentList(lldb::eArgTypeProtocol, eArgRepeatPlain);
+  }
+
+  ~CommandObjectProtocolServerGet() override = default;
+
+protected:
+  void DoExecute(Args &args, CommandReturnObject &result) override {
+    if (args.GetArgumentCount() < 1) {
+      result.AppendError("no protocol specified");
+      return;
+    }
+
+    llvm::StringRef protocol = args.GetArgumentAtIndex(0);
+    ProtocolServer *server = ProtocolServer::GetOrCreate(protocol);
+    if (!server) {
+      result.AppendErrorWithFormatv(
+          "unsupported protocol: {0}. Supported protocols are: {1}", protocol,
+          llvm::join(ProtocolServer::GetSupportedProtocols(), ", "));
+      return;
+    }
+
+    Socket *socket = server->GetSocket();
+    if (!socket) {
+      result.AppendErrorWithFormatv("{0} server is not running", protocol);
+      return;
+    }
+
+    std::string address =
+        llvm::join(socket->GetListeningConnectionURI(), ", ");
+    result.AppendMessageWithFormatv(
+        "{0} server connection listeners: {1}", protocol, address);
+    result.SetStatus(eReturnStatusSuccessFinishNoResult);
+  }
+};
+
 CommandObjectProtocolServer::CommandObjectProtocolServer(
     CommandInterpreter &interpreter)
     : CommandObjectMultiword(interpreter, "protocol-server",
-                             "Start and stop a protocol server.",
+                             "Start, stop, and query protocol servers.",
                              "protocol-server") {
   LoadSubCommand("start", CommandObjectSP(new CommandObjectProtocolServerStart(
                               interpreter)));
   LoadSubCommand("stop", CommandObjectSP(
                              new CommandObjectProtocolServerStop(interpreter)));
+  LoadSubCommand("get", CommandObjectSP(
+                            new CommandObjectProtocolServerGet(interpreter)));
 }
 
 CommandObjectProtocolServer::~CommandObjectProtocolServer() = default;
diff --git a/lldb/source/Plugins/Protocol/MCP/ProtocolServerMCP.cpp b/lldb/source/Plugins/Protocol/MCP/ProtocolServerMCP.cpp
index 33bdd5eec3644..390cf3eeb16a5 100644
--- a/lldb/source/Plugins/Protocol/MCP/ProtocolServerMCP.cpp
+++ b/lldb/source/Plugins/Protocol/MCP/ProtocolServerMCP.cpp
@@ -144,6 +144,7 @@ llvm::Error ProtocolServerMCP::Stop() {
 
   m_server.reset(nullptr);
   m_server_info_handle.Remove();
+  m_listener.reset();
 
   return llvm::Error::success();
 }
diff --git a/lldb/test/API/commands/protocol/TestMCPUnixSocket.py b/lldb/test/API/commands/protocol/TestMCPUnixSocket.py
index ea9255cc60ef5..9edb97eb791b9 100644
--- a/lldb/test/API/commands/protocol/TestMCPUnixSocket.py
+++ b/lldb/test/API/commands/protocol/TestMCPUnixSocket.py
@@ -32,3 +32,16 @@ def test_unix_socket(self):
             startstr="MCP server started with connection listeners:",
             substrs=[f"unix-connect://{socket_file}"],
         )
+
+        self.expect(
+            "protocol-server get MCP",
+            startstr="MCP server connection listeners:",
+            substrs=[f"unix-connect://{socket_file}"],
+        )
+
+        self.runCmd("protocol-server stop MCP", check=False)
+        self.expect(
+            "protocol-server get MCP",
+            error=True,
+            substrs=["MCP server is not running"],
+        )

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[JDevlieghere]

Looks useful, LGTM

[splhack]

Nice!

Is it possible to add --json option or Python API as follow up? So that Python script could get the status reliably without worrying about stdout format change.

[aperez]

@splhack I can put up a PR with a --json option as follow up.