feat: add HOST environment variable for configurable bind address

[mjfork]

Summary

• Add HOST environment variable to configure which host/IP the servers bind to
• Default to 0.0.0.0 (all interfaces) for backward compatibility
• Update both Express server and Vite dev server to respect the HOST setting

Fixes #359

Changes

• .env.example: Added HOST environment variable with documentation
• server/index.js: Use HOST env var instead of hardcoded '0.0.0.0'
• vite.config.js: Added host option to Vite server config

Test plan

• Set HOST=127.0.0.1 and verify server only listens on localhost
• Leave HOST unset and verify server listens on all interfaces (default behavior)
• Verify both backend server and Vite dev server respect the HOST setting

🤖 Generated with Claude Code

Summary by CodeRabbit

• Chores
  • Server and dev tooling now respect a configurable host and port via environment variables, making it easier to change the network interface without code edits.
  • Local URLs shown in logs and dev proxies normalize a bind-all address to "localhost" for clearer, user-friendly links.

_{✏️ Tip: You can customize this high-level summary in your review settings.}

[coderabbitai]

Walkthrough

Adds a configurable HOST environment variable (default 0.0.0.0) and updates server and Vite dev server startup/logging to use that value, mapping 0.0.0.0 to localhost for display purposes.

Changes

Cohort / File(s)	Summary
Environment Example \.env.example	Added HOST entry with default 0.0.0.0 and comments explaining binding behavior and localhost mapping.
Server & Dev Server server/index.js, vite.config.js	Read HOST from environment (default 0.0.0.0); compute a display/proxy host (localhost when binding to 0.0.0.0); use HOST for listen/serve and update logs/proxy targets accordingly.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

🐇 I nibble bytes and sniff the net,
HOST set free — no longer met,
Bind where you wish, near or far,
I hop between localhost and star,
Cheers from a rabbit, code and carrot char! 🥕

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The PR title accurately summarizes the main change: adding a HOST environment variable for configurable bind address, which matches the primary objective of the changeset.
Linked Issues check	✅ Passed	All requirements from issue #359 are met: HOST env var added to .env.example with documentation, server/index.js updated to use HOST, and vite.config.js configured to respect HOST settings.
Out of Scope Changes check	✅ Passed	All changes are directly related to the HOST environment variable feature. The DISPLAY_HOST logic and proxy configuration enhancements align with the objective of making the feature functional and user-friendly.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[coderabbitai]

Actionable comments posted: 0

Caution

Some comments are outside the diff and can’t be posted inline due to platform limitations.

⚠️ Outside diff range comments (1)

vite.config.js (1)

11-22: ⚠️ Potential issue | 🟠 Major

Proxy targets ignore HOST and can break non-local binds.
If HOST is set to a specific interface (e.g., 192.168.1.100), the backend binds only there, but the Vite proxy still targets localhost, which will fail. Use a derived proxyHost that falls back to localhost only when HOST=0.0.0.0.

🐛 Proposed fix

 export default defineConfig(({ command, mode }) => {
   // Load env file based on `mode` in the current working directory.
   const env = loadEnv(mode, process.cwd(), '')
+  const host = env.HOST || '0.0.0.0'
+  const proxyHost = host === '0.0.0.0' ? 'localhost' : host
   
   return {
     plugins: [react()],
     server: {
-      host: env.HOST || '0.0.0.0',
+      host,
       port: parseInt(env.VITE_PORT) || 5173,
       proxy: {
-        '/api': `http://localhost:${env.PORT || 3001}`,
+        '/api': `http://${proxyHost}:${env.PORT || 3001}`,
         '/ws': {
-          target: `ws://localhost:${env.PORT || 3001}`,
+          target: `ws://${proxyHost}:${env.PORT || 3001}`,
           ws: true
         },
         '/shell': {
-          target: `ws://localhost:${env.PORT || 3001}`,
+          target: `ws://${proxyHost}:${env.PORT || 3001}`,
           ws: true
         }
       }
     },

🧹 Nitpick comments (1)

server/index.js (1)

1801-1829: Consider a user-friendly URL when HOST is 0.0.0.0.
Line 1829 will print http://0.0.0.0:PORT, which isn’t a connectable URL for most users. A display host (e.g., localhost when bound to all interfaces) avoids confusion.

♻️ Suggested tweak

-const HOST = process.env.HOST || '0.0.0.0';
+const HOST = process.env.HOST || '0.0.0.0';
+const DISPLAY_HOST = HOST === '0.0.0.0' ? 'localhost' : HOST;
...
-            console.log(`${c.info('[INFO]')} Server URL:  ${c.bright('http://' + HOST + ':' + PORT)}`);
+            console.log(`${c.info('[INFO]')} Server URL:  ${c.bright('http://' + DISPLAY_HOST + ':' + PORT)}`);