Make port 0 mean pick an unused port

README.md

@@ -84,6 +84,10 @@ The host and port are associated with the event loop, and are remembered until
 the server is closed. Attempting to connect after closing the server, or to an
 address that hasn't been registered, will raise a `ConnectionRefusedError`.
 
+If you don't want the bother of picking non-colliding ports, you can pass a
+port number of 0, and async-solipsism will bind the first port number above
+60000 that is unused.
+
 ### Integration with pytest-asyncio
 
 async-solipsism and pytest-asyncio complement each other well: just write a
@@ -117,7 +121,7 @@ def event_loop():
 
 
 def socket_factory(host, port, family):
-    return async_solipsism.ListenSocket((host, port if port else 80))
+    return async_solipsism.ListenSocket((host, port))
 
 
 async def test_integration():
@@ -134,10 +138,6 @@ the socket factory, although it may be possible to do by monkeypatching. In
 practice you will probably want to define your own fixtures for the client
 and server.
 
-If you need to run more than one test server concurrently, you'll need to
-extend the socket factory to assign them each a different port
-(async-solipsism does not currently handle mapping port 0 to an unused port).
-
 ## Limitations
 
 The requirement to have no interaction with the outside world naturally
@@ -167,12 +167,16 @@ Calling functions that are not supported will generally raise
 
 ## Changelog
 
+### 0.5
+
+- Map port 0 to an unused port.
+
 ### 0.4
 
 - Allow `call_soon_threadsafe` from the same thread.
 - Don't warn when `SO_KEEPALIVE` is set on a socket.
 - Update instructions for use with aiohttp.
-- Add a pyproject.toml
+- Add a pyproject.toml.
 
 ### 0.3
 

src/async_solipsism/__init__.py

@@ -1,4 +1,4 @@
-# Copyright 2020-2021 Bruce Merry
+# Copyright 2020-2022 Bruce Merry
 #
 # This file is part of async-solipsism.
 #
@@ -19,4 +19,4 @@
 from .socket import *      # noqa
 from .loop import *        # noqa
 
-__version__ = '0.4'
+__version__ = '0.5'

src/async_solipsism/loop.py

@@ -113,8 +113,14 @@ async def create_server(
             # TODO: what if host is actually a list?
             addr = (host, port, 0, 0)
             sock = _socket.ListenSocket(addr)
-        else:
-            addr = sock.getsockname()
+        addr = sock.getsockname()
+        if addr[1] == 0:  # Port 0: pick a free port
+            addr_list = list(addr)
+            addr_list[1] = 60000
+            while tuple(addr_list) in self.__listening_sockets:
+                addr_list[1] += 1
+            addr = tuple(addr_list)
+            sock._sockname = addr
         if addr in self.__listening_sockets:
             raise SolipsismError("Reuse of listening addresses is not supported")
         self.__listening_sockets[addr] = sock

test/test_loop.py

@@ -1,4 +1,4 @@
-# Copyright 2020 Bruce Merry
+# Copyright 2020, 2022 Bruce Merry
 #
 # This file is part of async-solipsism.
 #
@@ -156,6 +156,18 @@ def callback(reader, writer):
     await server.wait_closed()
 
 
+async def test_unused_port(event_loop):
+    def callback(reader, writer):
+        pass
+
+    listen_socket1 = async_solipsism.ListenSocket(('localhost', 0))
+    listen_socket2 = async_solipsism.ListenSocket(('localhost', 0))
+    server1 = await asyncio.start_server(callback, sock=listen_socket1)
+    server2 = await asyncio.start_server(callback, sock=listen_socket2)
+    assert listen_socket1.getsockname()[1] == 60000
+    assert listen_socket2.getsockname()[1] == 60001
+
+
 async def test_close_server(event_loop):
     server = await asyncio.start_server(lambda reader, writer: None, 'test.invalid', 1234)
     server.close()