feat(mcp-server): add DRAWIO_BASE_URL env for private deployments (#467)

* feat(mcp-server): add DRAWIO_BASE_URL env for private deployments

* Fix postMessage origin check and URL normalization

- Add getOrigin() function to extract scheme+host+port from DRAWIO_BASE_URL
- Use DRAWIO_ORIGIN for postMessage security check instead of full URL
- Add normalizeUrl() to remove trailing slash and avoid double slashes
- This fixes issues when users configure DRAWIO_BASE_URL with trailing slash or path

packages/mcp-server/README.md

@@ -90,7 +90,7 @@ Use the standard MCP configuration with:
 - **Natural Language**: Describe diagrams in plain text - flowcharts, architecture diagrams, etc.
 - **Edit Support**: Modify existing diagrams with natural language instructions
 - **Export**: Save diagrams as `.drawio` files
-- **Self-contained**: Embedded server, works offline (except draw.io UI which loads from embed.diagrams.net)
+- **Self-contained**: Embedded server, works offline (except draw.io UI which loads from `embed.diagrams.net` by default, configurable via `DRAWIO_BASE_URL`)
 
 ## Available Tools
 
@@ -130,6 +130,33 @@ Use the standard MCP configuration with:
 | Variable | Default | Description |
 |----------|---------|-------------|
 | `PORT` | `6002` | Port for the embedded HTTP server |
+| `DRAWIO_BASE_URL` | `https://embed.diagrams.net` | Base URL for the draw.io embed. Set this to use a self-hosted draw.io instance for private deployments. |
+
+### Private Deployment (Self-hosted draw.io)
+
+For security-sensitive environments that require private deployment of draw.io:
+
+```json
+{
+  "mcpServers": {
+    "drawio": {
+      "command": "npx",
+      "args": ["@next-ai-drawio/mcp-server@latest"],
+      "env": { 
+        "DRAWIO_BASE_URL": "https://drawio.your-company.com"
+      }
+    }
+  }
+}
+```
+
+You can deploy your own draw.io instance using the official Docker image:
+
+```bash
+docker run -d -p 8080:8080 jgraph/drawio
+```
+
+Then set `DRAWIO_BASE_URL=http://localhost:8080` (or your server's URL).
 
 ## Troubleshooting
 

packages/mcp-server/src/http-server.ts

@@ -13,6 +13,28 @@ import {
 } from "./history.js"
 import { log } from "./logger.js"
 
+// Configurable draw.io embed URL for private deployments
+const DRAWIO_BASE_URL =
+    process.env.DRAWIO_BASE_URL || "https://embed.diagrams.net"
+
+// Extract origin (scheme + host + port) from URL for postMessage security check
+function getOrigin(url: string): string {
+    try {
+        const parsed = new URL(url)
+        return `${parsed.protocol}//${parsed.host}`
+    } catch {
+        return url // Fallback if parsing fails
+    }
+}
+
+const DRAWIO_ORIGIN = getOrigin(DRAWIO_BASE_URL)
+
+// Normalize URL for iframe src - ensure no double slashes
+function normalizeUrl(url: string): string {
+    // Remove trailing slash to avoid double slashes
+    return url.replace(/\/$/, '')
+}
+
 interface SessionState {
     xml: string
     version: number
@@ -403,7 +425,7 @@ function getHtmlPage(sessionId: string): string {
             </div>
             <div id="status" class="status disconnected">Connecting...</div>
         </div>
-        <iframe id="drawio" src="https://embed.diagrams.net/?embed=1&proto=json&spin=1&libraries=1"></iframe>
+        <iframe id="drawio" src="${normalizeUrl(DRAWIO_BASE_URL)}/?embed=1&proto=json&spin=1&libraries=1"></iframe>
     </div>
     <button id="history-btn" title="History" ${sessionId ? "" : "disabled"}>
         <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2">
@@ -433,7 +455,7 @@ function getHtmlPage(sessionId: string): string {
         let pendingAiSvg = false;
 
         window.addEventListener('message', (e) => {
-            if (e.origin !== 'https://embed.diagrams.net') return;
+            if (e.origin !== '${DRAWIO_ORIGIN}') return;
             try {
                 const msg = JSON.parse(e.data);
                 if (msg.event === 'init') {