[sans-io] make context.server non-optional

this makes for a nicer API, we just check for a missing address now.

mitmproxy/proxy2/context.py

@@ -27,8 +27,9 @@ class Client(Connection):
 class Server(Connection):
     sni: Union[bytes, bool] = True
     """True: client SNI, False: no SNI, bytes: custom value"""
+    address: Optional[tuple]
 
-    def __init__(self, address):
+    def __init__(self, address: Optional[tuple]):
         self.address = address
 
 
@@ -38,17 +39,16 @@ class Context:
     """
 
     client: Client
-    server: Optional[Server]
+    server: Server
     options: Options
     layers: List["mitmproxy.proxy2.layer.Layer"]
 
     def __init__(
             self,
             client: Client,
-            server: Optional[Server],
             options: Options,
     ) -> None:
         self.client = client
-        self.server = server
         self.options = options
+        self.server = Server(None)
         self.layers = []

mitmproxy/proxy2/server.py

@@ -29,7 +29,7 @@ class ConnectionHandler(metaclass=abc.ABCMeta):
         addr = writer.get_extra_info('peername')
 
         self.client = Client(addr)
-        self.context = Context(self.client, None, options)
+        self.context = Context(self.client, options)
 
         if options.mode.startswith("reverse:"):
             self.layer = ReverseProxy(self.context)
@@ -83,6 +83,8 @@ class ConnectionHandler(metaclass=abc.ABCMeta):
                 break
 
     async def open_connection(self, command: commands.OpenConnection):
+        if not command.connection.address:
+            raise ValueError("Cannot open connection, no hostname given.")
         try:
             reader, writer = await asyncio.open_connection(
                 *command.connection.address