NethLink: connectivity check causes rate limiting (429) on startup with many clients

[edospadoni]

Problem

NethLink and phone-island use https://google.com to verify internet connectivity on startup. When many clients try to connect simultaneously, Google responds with HTTP 429 (Too Many Requests), causing:

• NethLink to get stuck on the splash screen
• Failed connectivity detection even when internet is available

Root Cause

• Full GET request to google.com downloads unnecessary HTML (~100KB+)
• Google's homepage is not designed for connectivity checks and applies rate limiting
• No fallback endpoints if Google fails

Solution

Replace with lightweight dedicated connectivity check endpoints:

1. Primary: https://connectivitycheck.gstatic.com/generate_204 - Google's official connectivity check (returns 204 No Content)
2. Fallback 1: https://1.1.1.1/cdn-cgi/trace - Cloudflare
3. Fallback 2: https://cloudflare.com/cdn-cgi/trace - Cloudflare alternative

Additional improvements:

• Use HEAD requests instead of GET (zero data transfer)
• Quick pre-check with net.isOnline() / navigator.onLine
• Reduced timeout from 5s to 3s per endpoint
• Sequential fallback on failure

Affected Projects

• nethlink
• phone-island

[edospadoni]

Test Case

Prerequisites

• NethLink built with the PR changes
• Access to the developer console (start with DEV=true)
• Ability to enable/disable network connection

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Test 1: Verify endpoints used

Goal: Verify that google.com is no longer used for connectivity checks

Steps:

1. Start NethLink with DEV=true
2. Observe the logs in the console during startup
3. Disconnect and reconnect the network

Expected:

• Logs must NOT show https://google.com
• Must show https://connectivitycheck.gstatic.com/generate_204 (dedicated Google endpoint)
• On primary endpoint failure, must show Cloudflare fallbacks:
  • https://1.1.1.1/cdn-cgi/trace
  • https://cloudflare.com/cdn-cgi/trace

---

Test 2: Simulate rate limiting (block primary endpoint)

Goal: Verify fallbacks work when primary endpoint fails

Steps:

1. Edit /etc/hosts adding:

   127.0.0.1 connectivitycheck.gstatic.com
   

2. Start NethLink
3. Observe the logs

Expected:

• Log must show failure on connectivitycheck.gstatic.com
• Must then try 1.1.1.1/cdn-cgi/trace
• App must start correctly using Cloudflare fallback

Cleanup:

• Remove the line added to /etc/hosts

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Test 3: Start without connection

Goal: Verify splash screen shows error dialog and allows retry

Steps:

1. Disconnect network (WiFi off or cable unplugged)
2. Start NethLink
3. Wait ~3 seconds (3 automatic attempts)

Expected:

• "No internet connection" dialog must appear on splash screen
• Dialog must have a "Refresh" button
• Logs must NOT print in continuous loop (automatic retry stops after 3 attempts)

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Test 4: Connection auto-recovery

Goal: Verify the app automatically detects when connection returns

Steps:

1. Start NethLink without connection (as in Test 3)
2. Wait for "No internet connection" dialog
3. Reconnect the network
4. Wait up to 5 seconds

Expected:

• Dialog must close automatically
• App must continue with startup/login
• Log must show: START - network came back online, retrying automatically

---

Test 5: Manual retry

Goal: Verify "Refresh" button works

Steps:

1. Start NethLink without connection
2. Wait for "No internet connection" dialog
3. Reconnect the network
4. Immediately click "Refresh" (before auto-recovery triggers)

Expected:

• Dialog must close
• App must retry connection
• App must continue with startup

[edospadoni]

Testing release:

• fix: use lightweight endpoints with fallbacks for connectivity check nethlink#87 (comment)