Fix server not running with explicit hostname

tests/test_main.py

@@ -33,6 +33,31 @@ def install_signal_handlers(self):
     thread.join()
 
 
+def test_run_hostname():
+    class App:
+        def __init__(self, scope):
+            if scope["type"] != "http":
+                raise Exception()
+
+        async def __call__(self, receive, send):
+            await send({"type": "http.response.start", "status": 204, "headers": []})
+            await send({"type": "http.response.body", "body": b"", "more_body": False})
+
+    class CustomServer(Server):
+        def install_signal_handlers(self):
+            pass
+
+    config = Config(app=App, host="localhost", loop="asyncio", limit_max_requests=1)
+    server = CustomServer(config=config)
+    thread = threading.Thread(target=server.run)
+    thread.start()
+    while not server.started:
+        time.sleep(0.01)
+    response = requests.get("http://localhost:8000")
+    assert response.status_code == 204
+    thread.join()
+
+
 def test_run_multiprocess():
     class App:
         def __init__(self, scope):

uvicorn/config.py

@@ -7,7 +7,6 @@
 import socket
 import ssl
 import sys
-from enum import Enum
 from typing import List, Tuple
 
 import click
@@ -116,15 +115,8 @@ def create_ssl_context(
     return ctx
 
 
-class _IPKind(Enum):
-    IPv4 = "IPv4"
-    IPv6 = "IPv6"
-
-
-def _get_server_start_message(
-    host_ip_version: _IPKind = _IPKind.IPv4,
-) -> Tuple[str, str]:
-    if host_ip_version is _IPKind.IPv6:
+def _get_server_start_message(is_ipv6_message: bool = False) -> Tuple[str, str]:
+    if is_ipv6_message:
         ip_repr = "%s://[%s]:%d"
     else:
         ip_repr = "%s://%s:%d"
@@ -376,9 +368,9 @@ def bind_socket(self):
         sock.set_inheritable(True)
 
         if family == socket.AddressFamily.AF_INET6:
-            message, color_message = _get_server_start_message(_IPKind.IPv6)
+            message, color_message = _get_server_start_message(is_ipv6_message=True)
         else:
-            message, color_message = _get_server_start_message(_IPKind.IPv4)
+            message, color_message = _get_server_start_message()
         protocol_name = "https" if self.is_ssl else "http"
         logger.info(
             message,

uvicorn/main.py

@@ -10,7 +10,7 @@
 import time
 import typing
 from email.utils import formatdate
-from ipaddress import IPv6Address, ip_address
+from ipaddress import IPv4Address, IPv6Address, ip_address
 
 import click
 
@@ -26,7 +26,6 @@
     WS_PROTOCOLS,
     Config,
     _get_server_start_message,
-    _IPKind,
 )
 from uvicorn.supervisors import ChangeReload, Multiprocess
 
@@ -523,10 +522,16 @@ def _share_socket(sock: socket) -> socket:
             if port == 0:
                 port = server.sockets[0].getsockname()[1]
             protocol_name = "https" if config.ssl else "http"
-            if isinstance(ip_address(config.host), IPv6Address):
-                message, color_message = _get_server_start_message(_IPKind.IPv6)
-            else:
-                message, color_message = _get_server_start_message(_IPKind.IPv4)
+            try:
+                addr = ip_address(config.host)
+                if isinstance(addr, IPv6Address):
+                    message, color_message = _get_server_start_message(
+                        is_ipv6_message=True
+                    )
+                elif isinstance(addr, IPv4Address):
+                    message, color_message = _get_server_start_message()
+            except ValueError:
+                message, color_message = _get_server_start_message()
 
             logger.info(
                 message,