Cleanup

src/ddns_service/dns.py

@@ -14,6 +14,75 @@ import dns.tsigkeyring
 import dns.update
 
 
+# Valid hostname label pattern (after punycode encoding)
+LABEL_PATTERN = re.compile(
+    r'^[a-z0-9]([a-z0-9-]{0,61}[a-z0-9])?$', re.IGNORECASE
+)
+
+
+class EncodingError(Exception):
+    """Raised when hostname encoding fails."""
+    pass
+
+
+def encode_dnsname(hostname):
+    """
+    Encode hostname to ASCII using punycode (IDNA).
+
+    Args:
+        hostname: Hostname string, possibly with unicode characters.
+
+    Returns:
+        ASCII-encoded hostname.
+
+    Raises:
+        EncodingError: If hostname is invalid.
+    """
+    hostname = hostname.lower().strip()
+
+    if not hostname:
+        raise EncodingError("Hostname cannot be empty")
+
+    # Remove trailing dot if present
+    if hostname.endswith('.'):
+        hostname = hostname[:-1]
+
+    if len(hostname) > 253:
+        raise EncodingError("Hostname too long (max 253 characters)")
+
+    try:
+        # Encode each label using IDNA
+        labels = hostname.split('.')
+        encoded_labels = []
+
+        for label in labels:
+            if not label:
+                raise EncodingError("Empty label in hostname")
+
+            # Encode to punycode if needed
+            try:
+                encoded = label.encode('idna').decode('ascii')
+            except UnicodeError as e:
+                raise EncodingError(f"Invalid label '{label}': {e}")
+
+            if len(encoded) > 63:
+                raise EncodingError(
+                    f"Label '{label}' too long (max 63 characters)"
+                )
+
+            if not LABEL_PATTERN.match(encoded):
+                raise EncodingError(f"Invalid label format: '{label}'")
+
+            encoded_labels.append(encoded)
+
+        return '.'.join(encoded_labels)
+
+    except EncodingError:
+        raise
+    except Exception as e:
+        raise EncodingError(f"Invalid hostname '{hostname}': {e}")
+
+
 def detect_ip_type(ip):
     try:
         addr = ipaddress.ip_address(ip)