Make sure socket.close() doesn't interfere with socket.makefile().

If a makefile()-generated object is open and its parent socket is
closed, the parent socket should remain open until the child is
closed, too.  The code to support this is moderately complex and
requires one extra slots in the socket object.

This change fixes httplib so that several urllib2net test cases pass
again.

Add SocketCloser class to socket.py, which encapsulates the
refcounting logic for sockets after makefile() has been called.

Move SocketIO class from io module to socket module.  It's only use is
to implement the raw I/O methods on top of a socket to support
makefile().

Add unittests to test_socket to cover various patterns of close and
makefile.

Lib/socket.py

@@ -89,22 +89,67 @@ if sys.platform.lower().startswith("win"):
 
 # True if os.dup() can duplicate socket descriptors.
 # (On Windows at least, os.dup only works on files)
-_can_dup_socket = hasattr(_socket, "dup")
+_can_dup_socket = hasattr(_socket.socket, "dup")
 
 if _can_dup_socket:
     def fromfd(fd, family=AF_INET, type=SOCK_STREAM, proto=0):
         nfd = os.dup(fd)
         return socket(family, type, proto, fileno=nfd)
 
+class SocketCloser:
+
+    """Helper to manage socket close() logic for makefile().
+
+    The OS socket should not be closed until the socket and all
+    of its makefile-children are closed.  If the refcount is zero
+    when socket.close() is called, this is easy: Just close the
+    socket.  If the refcount is non-zero when socket.close() is
+    called, then the real close should not occur until the last
+    makefile-child is closed.
+    """
+
+    def __init__(self, sock):
+        self._sock = sock
+        self._makefile_refs = 0
+        # Test whether the socket is open.
+        try:
+            sock.fileno()
+            self._socket_open = True
+        except error:
+            self._socket_open = False
+
+    def socket_close(self):
+        self._socket_open = False
+        self.close()
+
+    def makefile_open(self):
+        self._makefile_refs += 1
+
+    def makefile_close(self):
+        self._makefile_refs -= 1
+        self.close()
+
+    def close(self):
+        if not (self._socket_open or self._makefile_refs):
+            self._sock._real_close()
+
 
 class socket(_socket.socket):
 
     """A subclass of _socket.socket adding the makefile() method."""
 
-    __slots__ = ["__weakref__"]
+    __slots__ = ["__weakref__", "_closer"]
     if not _can_dup_socket:
         __slots__.append("_base")
 
+    def __init__(self, family=AF_INET, type=SOCK_STREAM, proto=0, fileno=None):
+        if fileno is None:
+            _socket.socket.__init__(self, family, type, proto)
+        else:
+            _socket.socket.__init__(self, family, type, proto, fileno)
+        # Defer creating a SocketCloser until makefile() is actually called.
+        self._closer = None
+
     def __repr__(self):
         """Wrap __repr__() to reveal the real class name."""
         s = _socket.socket.__repr__(self)
@@ -128,14 +173,6 @@ class socket(_socket.socket):
             conn.close()
         return wrapper, addr
 
-    if not _can_dup_socket:
-        def close(self):
-            """Wrap close() to close the _base as well."""
-            _socket.socket.close(self)
-            base = getattr(self, "_base", None)
-            if base is not None:
-                base.close()
-
     def makefile(self, mode="r", buffering=None, *,
                  encoding=None, newline=None):
         """Return an I/O stream connected to the socket.
@@ -156,7 +193,9 @@ class socket(_socket.socket):
             rawmode += "r"
         if writing:
             rawmode += "w"
-        raw = io.SocketIO(self, rawmode)
+        if self._closer is None:
+            self._closer = SocketCloser(self)
+        raw = SocketIO(self, rawmode, self._closer)
         if buffering is None:
             buffering = -1
         if buffering < 0:
@@ -183,6 +222,65 @@ class socket(_socket.socket):
         text.mode = mode
         return text
 
+    def close(self):
+        if self._closer is None:
+            self._real_close()
+        else:
+            self._closer.socket_close()
+
+    # _real_close calls close on the _socket.socket base class.
+
+    if not _can_dup_socket:
+        def _real_close(self):
+            _socket.socket.close(self)
+            base = getattr(self, "_base", None)
+            if base is not None:
+                self._base = None
+                base.close()
+    else:
+        def _real_close(self):
+            _socket.socket.close(self)
+
+
+class SocketIO(io.RawIOBase):
+
+    """Raw I/O implementation for stream sockets.
+
+    This class supports the makefile() method on sockets.  It provides
+    the raw I/O interface on top of a socket object.
+    """
+
+    # XXX More docs
+
+    def __init__(self, sock, mode, closer):
+        assert mode in ("r", "w", "rw")
+        io.RawIOBase.__init__(self)
+        self._sock = sock
+        self._mode = mode
+        self._closer = closer
+        closer.makefile_open()
+
+    def readinto(self, b):
+        return self._sock.recv_into(b)
+
+    def write(self, b):
+        return self._sock.send(b)
+
+    def readable(self):
+        return "r" in self._mode
+
+    def writable(self):
+        return "w" in self._mode
+
+    def fileno(self):
+        return self._sock.fileno()
+
+    def close(self):
+        if self.closed:
+            return
+        self._closer.makefile_close()
+        io.RawIOBase.close(self)
+
 
 def getfqdn(name=''):
     """Get fully qualified domain name from name.