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# These helpers are copied from test_support.py in the Python 2.7 standard
# library test suite.
import socket
# Don't use "localhost", since resolving it uses the DNS under recent
# Windows versions (see issue #18792).
HOST = "127.0.0.1"
HOSTv6 = "::1"
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.
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
the test. Which one to use depends on whether the calling code is creating
a python socket, or if an unused port needs to be provided in a constructor
or passed to an external program (i.e. the -accept argument to openssl's
s_server mode). Always prefer bind_port() over find_unused_port() where
possible. Hard coded ports should *NEVER* be used. As soon as a server
socket is bound to a hard coded port, the ability to run multiple instances
of the test simultaneously on the same host is compromised, which makes the
test a ticking time bomb in a buildbot environment. On Unix buildbots, this
may simply manifest as a failed test, which can be recovered from without
intervention in most cases, but on Windows, the entire python process can
completely and utterly wedge, requiring someone to log in to the buildbot
and manually kill the affected process.
(This is easy to reproduce on Windows, unfortunately, and can be traced to
the SO_REUSEADDR socket option having different semantics on Windows versus
Unix/Linux. On Unix, you can't have two AF_INET SOCK_STREAM sockets bind,
listen and then accept connections on identical host/ports. An EADDRINUSE
socket.error will be raised at some point (depending on the platform and
the order bind and listen were called on each socket).
However, on Windows, if SO_REUSEADDR is set on the sockets, no EADDRINUSE
will ever be raised when attempting to bind two identical host/ports. When
accept() is called on each socket, the second caller's process will steal
the port from the first caller, leaving them both in an awkwardly wedged
state where they'll no longer respond to any signals or graceful kills, and
must be forcibly killed via OpenProcess()/TerminateProcess().
The solution on Windows is to use the SO_EXCLUSIVEADDRUSE socket option
instead of SO_REUSEADDR, which effectively affords the same semantics as
SO_REUSEADDR on Unix. Given the propensity of Unix developers in the Open
Source world compared to Windows ones, this is a common mistake. A quick
look over OpenSSL's 0.9.8g source shows that they use SO_REUSEADDR when
openssl.exe is called with the 's_server' option, for example. See
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."""
tempsock = socket.socket(family, socktype)
port = bind_port(tempsock)
tempsock.close()
del tempsock
return port
def bind_port(sock, host=HOST):
"""Bind the socket to a free port and return the port number. Relies on
ephemeral ports in order to ensure we are using an unbound port. This is
important as many tests may be running simultaneously, especially in a
buildbot environment. This method raises an exception if the sock.family
is AF_INET and sock.type is SOCK_STREAM, *and* the socket has SO_REUSEADDR
or SO_REUSEPORT set on it. Tests should *never* set these socket options
for TCP/IP sockets. The only case for setting these options is testing
multicasting via multiple UDP sockets.
Additionally, if the SO_EXCLUSIVEADDRUSE socket option is available (i.e.
on Windows), it will be set on the socket. This will prevent anyone else
from bind()'ing to our host/port for the duration of the test.
"""
if sock.family == socket.AF_INET and sock.type == socket.SOCK_STREAM:
if hasattr(socket, 'SO_REUSEADDR'):
if sock.getsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR) == 1:
raise ValueError("tests should never set the SO_REUSEADDR " \
"socket option on TCP/IP sockets!")
if hasattr(socket, 'SO_REUSEPORT'):
if sock.getsockopt(socket.SOL_SOCKET, socket.SO_REUSEPORT) == 1:
raise ValueError("tests should never set the SO_REUSEPORT " \
"socket option on TCP/IP sockets!")
if hasattr(socket, 'SO_EXCLUSIVEADDRUSE'):
sock.setsockopt(socket.SOL_SOCKET, socket.SO_EXCLUSIVEADDRUSE, 1)
sock.bind((host, 0))
port = sock.getsockname()[1]
return port
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