From afd7eebf91299549ae09a310f1763464d89928a9 Mon Sep 17 00:00:00 2001
From: Brad Fitzpatrick <bradfitz@tailscale.com>
Date: Fri, 4 Apr 2025 09:17:35 -0700
Subject: [PATCH] cmd/tsmcp: add a MCP implementation

Change-Id: I6e2a391dfe0929e6c44a537456fb2ea4c06b603b
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
---
 cmd/tsmcp/tsmcp.go | 94 ++++++++++++++++++++++++++++++++++++++++++++++
 go.mod             |  2 +
 go.sum             |  4 ++
 3 files changed, 100 insertions(+)
 create mode 100644 cmd/tsmcp/tsmcp.go

diff --git a/cmd/tsmcp/tsmcp.go b/cmd/tsmcp/tsmcp.go
new file mode 100644
index 000000000..3016f8088
--- /dev/null
+++ b/cmd/tsmcp/tsmcp.go
@@ -0,0 +1,94 @@
+package main
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/mark3labs/mcp-go/mcp"
+	"github.com/mark3labs/mcp-go/server"
+	"tailscale.com/client/local"
+	"tailscale.com/ipn"
+)
+
+func main() {
+	var s Server
+	s.lc = new(local.Client)
+
+	// Create MCP server
+	s.ms = server.NewMCPServer(
+		"Tailscale",
+		"1.0.0",
+	)
+
+	// Add tool
+	toolStatus := mcp.NewTool("get_connection_status",
+		mcp.WithDescription("Check Tailscale's connection status"),
+		// mcp.WithString("name",
+		//     mcp.Required(),
+		//     mcp.Description("Name of the person to greet"),
+		// ),
+	)
+
+	s.ms.AddTool(toolStatus, s.statusHandler)
+
+	toolUp := mcp.NewTool("up",
+		mcp.WithDescription("Turn Tailscale on (run 'tailscale up')"),
+	)
+	s.ms.AddTool(toolUp, s.upHandler)
+
+	toolDown := mcp.NewTool("down",
+		mcp.WithDescription("Turn Tailscale off (run 'tailscale down')"),
+	)
+	s.ms.AddTool(toolDown, s.downHandler)
+
+	// Start the stdio server
+	if err := server.ServeStdio(s.ms); err != nil {
+		fmt.Printf("Server error: %v\n", err)
+	}
+}
+
+type Server struct {
+	lc *local.Client
+	ms *server.MCPServer
+}
+
+func (s *Server) statusHandler(ctx context.Context, request mcp.CallToolRequest) (*mcp.CallToolResult, error) {
+	status, err := s.lc.StatusWithoutPeers(ctx)
+	if err != nil {
+		return nil, fmt.Errorf("failed to get connection status: %w", err)
+	}
+	switch status.BackendState {
+	case "NoState":
+		return mcp.NewToolResultText("In 'NoState', meaning it's broken or wedged or hung or maybe very early in its startup life cycle. But probably broken."), nil
+	case "Starting":
+		return mcp.NewToolResultText("In 'Starting', meaning it's starting up, but not yet fully connected. In particular, the control plane connection might be up, but no DERP yet."), nil
+	default:
+		return mcp.NewToolResultText(status.BackendState), nil
+	}
+}
+
+func (s *Server) upHandler(ctx context.Context, request mcp.CallToolRequest) (*mcp.CallToolResult, error) {
+	_, err := s.lc.EditPrefs(ctx, &ipn.MaskedPrefs{
+		WantRunningSet: true,
+		Prefs: ipn.Prefs{
+			WantRunning: true,
+		},
+	})
+	if err != nil {
+		return nil, fmt.Errorf("failed to turn on Tailscale: %w", err)
+	}
+	return mcp.NewToolResultText("done"), nil
+}
+
+func (s *Server) downHandler(ctx context.Context, request mcp.CallToolRequest) (*mcp.CallToolResult, error) {
+	_, err := s.lc.EditPrefs(ctx, &ipn.MaskedPrefs{
+		WantRunningSet: true,
+		Prefs: ipn.Prefs{
+			WantRunning: false,
+		},
+	})
+	if err != nil {
+		return nil, fmt.Errorf("failed to turn off Tailscale: %w", err)
+	}
+	return mcp.NewToolResultText("done"), nil
+}
diff --git a/go.mod b/go.mod
index 8ca56a4b9..11d837134 100644
--- a/go.mod
+++ b/go.mod
@@ -57,6 +57,7 @@ require (
 	github.com/kballard/go-shellquote v0.0.0-20180428030007-95032a82bc51
 	github.com/klauspost/compress v1.17.11
 	github.com/kortschak/wol v0.0.0-20200729010619-da482cc4850a
+	github.com/mark3labs/mcp-go v0.18.0
 	github.com/mattn/go-colorable v0.1.13
 	github.com/mattn/go-isatty v0.0.20
 	github.com/mdlayher/genetlink v1.3.2
@@ -156,6 +157,7 @@ require (
 	github.com/santhosh-tekuri/jsonschema/v5 v5.3.1 // indirect
 	github.com/xen0n/gosmopolitan v1.2.2 // indirect
 	github.com/ykadowak/zerologlint v0.1.5 // indirect
+	github.com/yosida95/uritemplate/v3 v3.0.2 // indirect
 	go-simpler.org/musttag v0.9.0 // indirect
 	go-simpler.org/sloglint v0.5.0 // indirect
 	go.opentelemetry.io/auto/sdk v1.1.0 // indirect
diff --git a/go.sum b/go.sum
index ca1b5e30c..0970bce6d 100644
--- a/go.sum
+++ b/go.sum
@@ -656,6 +656,8 @@ github.com/maratori/testableexamples v1.0.0 h1:dU5alXRrD8WKSjOUnmJZuzdxWOEQ57+7s
 github.com/maratori/testableexamples v1.0.0/go.mod h1:4rhjL1n20TUTT4vdh3RDqSizKLyXp7K2u6HgraZCGzE=
 github.com/maratori/testpackage v1.1.1 h1:S58XVV5AD7HADMmD0fNnziNHqKvSdDuEKdPD1rNTU04=
 github.com/maratori/testpackage v1.1.1/go.mod h1:s4gRK/ym6AMrqpOa/kEbQTV4Q4jb7WeLZzVhVVVOQMc=
+github.com/mark3labs/mcp-go v0.18.0 h1:YuhgIVjNlTG2ZOwmrkORWyPTp0dz1opPEqvsPtySXao=
+github.com/mark3labs/mcp-go v0.18.0/go.mod h1:KmJndYv7GIgcPVwEKJjNcbhVQ+hJGJhrCCB/9xITzpE=
 github.com/matoous/godox v0.0.0-20230222163458-006bad1f9d26 h1:gWg6ZQ4JhDfJPqlo2srm/LN17lpybq15AryXIRcWYLE=
 github.com/matoous/godox v0.0.0-20230222163458-006bad1f9d26/go.mod h1:1BELzlh859Sh1c6+90blK8lbYy0kwQf1bYlBhBysy1s=
 github.com/matryer/is v1.4.0 h1:sosSmIWwkYITGrxZ25ULNDeKiMNzFSr4V/eqBQP0PeE=
@@ -989,6 +991,8 @@ github.com/yeya24/promlinter v0.2.0 h1:xFKDQ82orCU5jQujdaD8stOHiv8UN68BSdn2a8u8Y
 github.com/yeya24/promlinter v0.2.0/go.mod h1:u54lkmBOZrpEbQQ6gox2zWKKLKu2SGe+2KOiextY+IA=
 github.com/ykadowak/zerologlint v0.1.5 h1:Gy/fMz1dFQN9JZTPjv1hxEk+sRWm05row04Yoolgdiw=
 github.com/ykadowak/zerologlint v0.1.5/go.mod h1:KaUskqF3e/v59oPmdq1U1DnKcuHokl2/K1U4pmIELKg=
+github.com/yosida95/uritemplate/v3 v3.0.2 h1:Ed3Oyj9yrmi9087+NczuL5BwkIc4wvTb5zIM+UJPGz4=
+github.com/yosida95/uritemplate/v3 v3.0.2/go.mod h1:ILOh0sOhIJR3+L/8afwt/kE++YT040gmv5BQTMR2HP4=
 github.com/yuin/goldmark v1.1.25/go.mod h1:3hX8gzYuyVAZsxl0MRgGTJEmQBFcNTphYh9decYSb74=
 github.com/yuin/goldmark v1.1.27/go.mod h1:3hX8gzYuyVAZsxl0MRgGTJEmQBFcNTphYh9decYSb74=
 github.com/yuin/goldmark v1.1.32/go.mod h1:3hX8gzYuyVAZsxl0MRgGTJEmQBFcNTphYh9decYSb74=