Add context to find_unused_port (urllib3#1837)

test/port_helpers.py

@@ -2,6 +2,7 @@
 # library test suite.
 
 import socket
+from contextlib import contextmanager
 
 
 # Don't use "localhost", since resolving it uses the DNS under recent
@@ -10,13 +11,14 @@
 HOSTv6 = "::1"
 
 
+@contextmanager
 def find_unused_port(family=socket.AF_INET, socktype=socket.SOCK_STREAM):
     """Returns an unused port that should be suitable for binding.  This is
     achieved by creating a temporary socket with the same family and type as
     the 'sock' parameter (default is AF_INET, SOCK_STREAM), and binding it to
     the specified host address (defaults to 0.0.0.0) with the port set to 0,
-    eliciting an unused ephemeral port from the OS.  The temporary socket is
-    then closed and deleted, and the ephemeral port is returned.
+    eliciting an unused ephemeral port from the OS. The ephemeral port is
+    yielded, and finally the temporary socket is closed and deleted.
 
     Either this method or bind_port() should be used for any tests where a
     server socket needs to be bound to a particular port for the duration of
@@ -56,19 +58,12 @@ def find_unused_port(family=socket.AF_INET, socktype=socket.SOCK_STREAM):
     http://bugs.python.org/issue2550 for more info.  The following site also
     has a very thorough description about the implications of both REUSEADDR
     and EXCLUSIVEADDRUSE on Windows:
-    http://msdn2.microsoft.com/en-us/library/ms740621(VS.85).aspx)
-
-    XXX: although this approach is a vast improvement on previous attempts to
-    elicit unused ports, it rests heavily on the assumption that the ephemeral
-    port returned to us by the OS won't immediately be dished back out to some
-    other process when we close and delete our temporary socket but before our
-    calling code has a chance to bind the returned port.  We can deal with this
-    issue if/when we come across it."""
+    http://msdn2.microsoft.com/en-us/library/ms740621(VS.85).aspx)"""
     tempsock = socket.socket(family, socktype)
     port = bind_port(tempsock)
+    yield port
     tempsock.close()
     del tempsock
-    return port
 
 
 def bind_port(sock, host=HOST):

test/with_dummyserver/test_connectionpool.py

@@ -349,11 +349,11 @@ def test_defaults_are_applied(self):
 
     def test_connection_error_retries(self):
         """ ECONNREFUSED error should raise a connection error, with retries """
-        port = find_unused_port()
-        with HTTPConnectionPool(self.host, port) as pool:
-            with pytest.raises(MaxRetryError) as e:
-                pool.request("GET", "/", retries=Retry(connect=3))
-            assert type(e.value.reason) == NewConnectionError
+        with find_unused_port() as port:
+            with HTTPConnectionPool(self.host, port) as pool:
+                with pytest.raises(MaxRetryError) as e:
+                    pool.request("GET", "/", retries=Retry(connect=3))
+                assert type(e.value.reason) == NewConnectionError
 
     def test_timeout_success(self):
         timeout = Timeout(connect=3, read=5, total=None)