Implemented public DNS resolution checks

checks.py

@@ -1,6 +1,7 @@
 import asyncio
 import json
 import time
+from urllib.parse import urlparse
 
 import aiohttp
 
@@ -24,6 +25,11 @@ TARGETS = [
 
 GITEA_VERSION_URL = 'https://gitea.rainbow-herring.ts.net/api/v1/version'
 
+DOH_RESOLVERS = {
+    'Cloudflare': 'https://cloudflare-dns.com/dns-query',
+    'Google': 'https://dns.google/resolve',
+}
+
 
 async def _get(session, url, timeout):
     started = time.monotonic()
@@ -37,6 +43,38 @@ async def _get(session, url, timeout):
         return resp.status, latency_ms, body
 
 
+async def _resolve_public(session, resolver_url, host, timeout):
+    try:
+        async with session.get(
+            resolver_url,
+            params={'name': host, 'type': 'A'},
+            headers={'Accept': 'application/dns-json'},
+            timeout=aiohttp.ClientTimeout(total=timeout),
+        ) as resp:
+            if resp.status != 200:
+                return {'ok': False, 'ips': [], 'error': f'HTTP {resp.status}'}
+            body = await resp.text()
+            data = json.loads(body)
+    except asyncio.TimeoutError:
+        return {'ok': False, 'ips': [], 'error': 'timeout'}
+    except aiohttp.ClientError:
+        return {'ok': False, 'ips': [], 'error': 'error'}
+    except Exception:
+        return {'ok': False, 'ips': [], 'error': 'error'}
+
+    status = data.get('Status')
+    if status == 3:
+        return {'ok': False, 'ips': [], 'error': 'NXDOMAIN'}
+    if status == 2:
+        return {'ok': False, 'ips': [], 'error': 'SERVFAIL'}
+    if status != 0:
+        return {'ok': False, 'ips': [], 'error': f'status {status}'}
+    answers = [a for a in data.get('Answer', []) if a.get('type') == 1]
+    if not answers:
+        return {'ok': False, 'ips': [], 'error': 'no A record'}
+    return {'ok': True, 'ips': [a['data'] for a in answers], 'error': ''}
+
+
 async def check_target(session, target, timeout):
     result = {
         'name': target['name'],
@@ -48,6 +86,7 @@ async def check_target(session, target, timeout):
         'db': None,
         'version': None,
         'detail': '',
+        'dns': {},
     }
     try:
         status, latency_ms, body = await _get(session, target['url'], timeout)
@@ -80,6 +119,10 @@ async def check_target(session, target, timeout):
         except Exception:
             pass
 
+    host = urlparse(target['url']).hostname
+    for label, resolver_url in DOH_RESOLVERS.items():
+        result['dns'][label] = await _resolve_public(session, resolver_url, host, timeout)
+
     return result