Allow raw ip addresses

app/dns_resolver.py

@@ -9,6 +9,7 @@ server given for that specific endpoint.
 from __future__ import annotations
 
 import contextlib
+import ipaddress
 import socket
 import threading
 
@@ -20,6 +21,35 @@ import dns.resolver
 _patch_lock = threading.Lock()
 
 
+def is_ip_literal(host: str) -> bool:
+    """Return True if `host` is already a literal IPv4 or IPv6 address.
+
+    Such hosts have nothing to resolve — dnspython does not special-case
+    them, it will happily send a DNS query for e.g. "192.168.0.2" as if it
+    were a hostname and get NXDOMAIN back. Callers should skip resolution
+    entirely for these.
+    """
+    try:
+        ipaddress.ip_address(host)
+        return True
+    except ValueError:
+        return False
+
+
+def format_host_for_url(host: str) -> str:
+    """Format `host` for embedding directly in a URL.
+
+    IPv6 literals need brackets (e.g. "::1" -> "[::1]"); everything else
+    (hostnames, IPv4 literals) is returned unchanged.
+    """
+    try:
+        if ipaddress.ip_address(host).version == 6:
+            return f"[{host}]"
+    except ValueError:
+        pass
+    return host
+
+
 def resolve(host: str, dns_server: str, timeout: float) -> str:
     """Resolve `host` to an IPv4 address using *only* `dns_server`.