Introduce VSCode companion extension (#3917)

2 files changed, 123 insertions, 0 deletions

diff --git a/packages/vscode-ide-companion/src/extension.ts b/packages/vscode-ide-companion/src/extension.ts
new file mode 100644
index 00000000..ecc63048
--- /dev/null
+++ b/packages/vscode-ide-companion/src/extension.ts
@@ -0,0 +1,14 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import * as vscode from 'vscode';
+import { startIDEServer } from './ide-server';
+
+export async function activate(context: vscode.ExtensionContext) {
+  startIDEServer(context);
+}
+
+export function deactivate() {}
diff --git a/packages/vscode-ide-companion/src/ide-server.ts b/packages/vscode-ide-companion/src/ide-server.ts
new file mode 100644
index 00000000..6d25367c
--- /dev/null
+++ b/packages/vscode-ide-companion/src/ide-server.ts
@@ -0,0 +1,109 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import * as vscode from 'vscode';
+import { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js';
+import { StreamableHTTPServerTransport } from '@modelcontextprotocol/sdk/server/streamableHttp.js';
+import express, { Request, Response } from 'express';
+
+export async function startIDEServer(_context: vscode.ExtensionContext) {
+  const app = express();
+  app.use(express.json());
+
+  const mcpServer = createMcpServer();
+  const transport = new StreamableHTTPServerTransport({
+    sessionIdGenerator: undefined,
+    enableJsonResponse: true,
+  });
+
+  mcpServer.connect(transport);
+
+  app.post('/mcp', async (req: Request, res: Response) => {
+    console.log('Received MCP request:', req.body);
+    try {
+      await transport.handleRequest(req, res, req.body);
+    } catch (error) {
+      console.error('Error handling MCP request:', error);
+      if (!res.headersSent) {
+        res.status(500).json({
+          jsonrpc: '2.0',
+          error: {
+            code: -32603,
+            message: 'Internal server error',
+          },
+          id: null,
+        });
+      }
+    }
+  });
+
+  // Handle GET requests for SSE streams
+  app.get('/mcp', async (req: Request, res: Response) => {
+    res.status(405).set('Allow', 'POST').send('Method Not Allowed');
+  });
+
+  // Start the server
+  // TODO(#3918): Generate dynamically and write to env variable
+  const PORT = 3000;
+  app.listen(PORT, (error) => {
+    if (error) {
+      console.error('Failed to start server:', error);
+      vscode.window.showErrorMessage(
+        `Companion server failed to start on port ${PORT}: ${error.message}`,
+      );
+    }
+    console.log(`MCP Streamable HTTP Server listening on port ${PORT}`);
+  });
+}
+
+const createMcpServer = () => {
+  const server = new McpServer({
+    name: 'vscode-ide-server',
+    version: '1.0.0',
+  });
+  server.registerTool(
+    'getActiveFile',
+    {
+      description:
+        '(IDE Tool) Get the path of the file currently active in VS Code.',
+      inputSchema: {},
+    },
+    async () => {
+      try {
+        const activeEditor = vscode.window.activeTextEditor;
+        const filePath = activeEditor
+          ? activeEditor.document.uri.fsPath
+          : undefined;
+        if (filePath) {
+          return {
+            content: [{ type: 'text', text: `Active file: ${filePath}` }],
+          };
+        } else {
+          return {
+            content: [
+              {
+                type: 'text',
+                text: 'No file is currently active in the editor.',
+              },
+            ],
+          };
+        }
+      } catch (error) {
+        return {
+          content: [
+            {
+              type: 'text',
+              text: `Failed to get active file: ${
+                (error as Error).message || 'Unknown error'
+              }`,
+            },
+          ],
+        };
+      }
+    },
+  );
+  return server;
+};