from __future__ import print_function, division, absolute_import

import collections
from contextlib import contextmanager
from datetime import timedelta
import functools
import gc
from glob import glob
import itertools
import inspect
import logging
import logging.config
import os
import re
import shutil
import signal
import socket
import subprocess
import sys
import tempfile
import textwrap
import threading
from time import sleep
import uuid
import weakref

try:
    import ssl
except ImportError:
    ssl = None

import pytest
import six

from dask.context import _globals
from toolz import merge, memoize
from tornado import gen, queues
from tornado.gen import TimeoutError
from tornado.ioloop import IOLoop

from .compatibility import PY3, iscoroutinefunction
from .config import config, initialize_logging
from .core import connect, rpc, CommClosedError
from .metrics import time
from .proctitle import enable_proctitle_on_children
from .security import Security
from .utils import (ignoring, log_errors, mp_context, get_ip, get_ipv6,
                    DequeHandler, reset_logger_locks)
from .worker import Worker, TOTAL_MEMORY


logger = logging.getLogger(__name__)


logging_levels = {name: logger.level for name, logger in
                  logging.root.manager.loggerDict.items()
                  if isinstance(logger, logging.Logger)}


@pytest.fixture(scope='session')
def valid_python_script(tmpdir_factory):
    local_file = tmpdir_factory.mktemp('data').join('file.py')
    local_file.write("print('hello world!')")
    return local_file


@pytest.fixture(scope='session')
def client_contract_script(tmpdir_factory):
    local_file = tmpdir_factory.mktemp('data').join('distributed_script.py')
    lines = ("from distributed import Client", "e = Client('127.0.0.1:8989')",
             'print(e)')
    local_file.write('\n'.join(lines))
    return local_file


@pytest.fixture(scope='session')
def invalid_python_script(tmpdir_factory):
    local_file = tmpdir_factory.mktemp('data').join('file.py')
    local_file.write("a+1")
    return local_file


@pytest.fixture
def loop():
    with pristine_loop() as loop:
        # Monkey-patch IOLoop.start to wait for loop stop
        orig_start = loop.start
        is_stopped = threading.Event()
        is_stopped.set()

        def start():
            is_stopped.clear()
            try:
                orig_start()
            finally:
                is_stopped.set()
        loop.start = start

        yield loop
        # Stop the loop in case it's still running
        try:
            loop.add_callback(loop.stop)
        except RuntimeError as e:
            if not re.match("IOLoop is clos(ed|ing)", str(e)):
                raise
        else:
            is_stopped.wait()


@pytest.fixture
def loop_in_thread():
    with pristine_loop() as loop:
        thread = threading.Thread(target=loop.start,
                                  name="test IOLoop")
        thread.daemon = True
        thread.start()
        loop_started = threading.Event()
        loop.add_callback(loop_started.set)
        loop_started.wait()
        yield loop
        loop.add_callback(loop.stop)
        thread.join(timeout=5)


@pytest.fixture
def zmq_ctx():
    import zmq
    ctx = zmq.Context.instance()
    yield ctx
    ctx.destroy(linger=0)


@contextmanager
def pristine_loop():
    IOLoop.clear_instance()
    IOLoop.clear_current()
    loop = IOLoop()
    loop.make_current()
    assert IOLoop.current() is loop
    try:
        yield loop
    finally:
        try:
            loop.close(all_fds=True)
        except ValueError:
            pass
        IOLoop.clear_instance()
        IOLoop.clear_current()


@contextmanager
def mock_ipython():
    import mock
    from distributed._ipython_utils import remote_magic
    ip = mock.Mock()
    ip.user_ns = {}
    ip.kernel = None

    def get_ip():
        return ip

    with mock.patch('IPython.get_ipython', get_ip), \
            mock.patch('distributed._ipython_utils.get_ipython', get_ip):
        yield ip
    # cleanup remote_magic client cache
    for kc in remote_magic._clients.values():
        kc.stop_channels()
    remote_magic._clients.clear()


def nodebug(func):
    """
    A decorator to disable debug facilities during timing-sensitive tests.
    Warning: this doesn't affect already created IOLoops.
    """
    if not PY3:
        # py.test's runner magic breaks horridly on Python 2
        # when a test function is wrapped, so avoid it
        # (incidently, asyncio is irrelevant anyway)
        return func

    @functools.wraps(func)
    def wrapped(*args, **kwargs):
        old_asyncio_debug = os.environ.get("PYTHONASYNCIODEBUG")
        if old_asyncio_debug is not None:
            del os.environ["PYTHONASYNCIODEBUG"]
        try:
            return func(*args, **kwargs)
        finally:
            if old_asyncio_debug is not None:
                os.environ["PYTHONASYNCIODEBUG"] = old_asyncio_debug

    return wrapped


def nodebug_setup_module(module):
    """
    A setup_module() that you can install in a test module to disable
    debug facilities.
    """
    module._old_asyncio_debug = os.environ.get("PYTHONASYNCIODEBUG")
    if module._old_asyncio_debug is not None:
        del os.environ["PYTHONASYNCIODEBUG"]


def nodebug_teardown_module(module):
    """
    A teardown_module() that you can install in a test module to reenable
    debug facilities.
    """
    if module._old_asyncio_debug is not None:
        os.environ["PYTHONASYNCIODEBUG"] = module._old_asyncio_debug


def inc(x):
    return x + 1


def dec(x):
    return x - 1


def mul(x, y):
    return x * y


def div(x, y):
    return x / y


def deep(n):
    if n > 0:
        return deep(n - 1)
    else:
        return True


def throws(x):
    raise RuntimeError('hello!')


def double(x):
    return x * 2


def slowinc(x, delay=0.02):
    sleep(delay)
    return x + 1


def slowdec(x, delay=0.02):
    sleep(delay)
    return x - 1


def slowdouble(x, delay=0.02):
    sleep(delay)
    return 2 * x


def randominc(x, scale=1):
    from random import random
    sleep(random() * scale)
    return x + 1


def slowadd(x, y, delay=0.02):
    sleep(delay)
    return x + y


def slowsum(seq, delay=0.02):
    sleep(delay)
    return sum(seq)


def slowidentity(*args, **kwargs):
    delay = kwargs.get('delay', 0.02)
    sleep(delay)
    if len(args) == 1:
        return args[0]
    else:
        return args


def run_for(duration, timer=time):
    """
    Burn CPU for *duration* seconds.
    """
    deadline = timer() + duration
    while timer() <= deadline:
        pass


# This dict grows at every varying() invocation
_varying_dict = collections.defaultdict(int)
_varying_key_gen = itertools.count()


class _ModuleSlot(object):
    def __init__(self, modname, slotname):
        self.modname = modname
        self.slotname = slotname

    def get(self):
        return getattr(sys.modules[self.modname], self.slotname)


def varying(items):
    """
    Return a function that returns a result (or raises an exception)
    from *items* at each call.
    """
    # cloudpickle would serialize the *values* of all globals
    # used by *func* below, so we can't use `global <something>`.
    # Instead look up the module by name to get the original namespace
    # and not a copy.
    slot = _ModuleSlot(__name__, '_varying_dict')
    key = next(_varying_key_gen)

    def func():
        dct = slot.get()
        i = dct[key]
        if i == len(items):
            raise IndexError
        else:
            x = items[i]
            dct[key] = i + 1
            if isinstance(x, Exception):
                raise x
            else:
                return x

    return func


def map_varying(itemslists):
    """
    Like *varying*, but return the full specification for a map() call
    on multiple items lists.
    """
    def apply(func, *args, **kwargs):
        return func(*args, **kwargs)

    return apply, map(varying, itemslists)


@gen.coroutine
def geninc(x, delay=0.02):
    yield gen.sleep(delay)
    raise gen.Return(x + 1)


def compile_snippet(code, dedent=True):
    if dedent:
        code = textwrap.dedent(code)
    code = compile(code, '<dynamic>', 'exec')
    ns = globals()
    exec(code, ns, ns)


if sys.version_info >= (3, 5):
    compile_snippet("""
        async def asyncinc(x, delay=0.02):
            await gen.sleep(delay)
            return x + 1
        """)
    assert asyncinc  # noqa: F821
else:
    asyncinc = None


_readone_queues = {}


@gen.coroutine
def readone(comm):
    """
    Read one message at a time from a comm that reads lists of
    messages.
    """
    try:
        q = _readone_queues[comm]
    except KeyError:
        q = _readone_queues[comm] = queues.Queue()

        @gen.coroutine
        def background_read():
            while True:
                try:
                    messages = yield comm.read()
                except CommClosedError:
                    break
                for msg in messages:
                    q.put_nowait(msg)
            q.put_nowait(None)
            del _readone_queues[comm]

        background_read()

    msg = yield q.get()
    if msg is None:
        raise CommClosedError
    else:
        raise gen.Return(msg)


def run_scheduler(q, nputs, **kwargs):
    from distributed import Scheduler

    # On Python 2.7 and Unix, fork() is used to spawn child processes,
    # so avoid inheriting the parent's IO loop.
    with pristine_loop() as loop:
        scheduler = Scheduler(validate=True, **kwargs)
        done = scheduler.start('127.0.0.1')

        for i in range(nputs):
            q.put(scheduler.address)
        try:
            loop.start()
        finally:
            loop.close(all_fds=True)


def run_worker(q, scheduler_q, **kwargs):
    from distributed import Worker

    reset_logger_locks()
    with log_errors():
        with pristine_loop() as loop:
            scheduler_addr = scheduler_q.get()
            worker = Worker(scheduler_addr, validate=True, **kwargs)
            loop.run_sync(lambda: worker._start(0))
            q.put(worker.address)
            try:
                @gen.coroutine
                def wait_until_closed():
                    yield worker._closed.wait()

                loop.run_sync(wait_until_closed)
            finally:
                loop.close(all_fds=True)


def run_nanny(q, scheduler_q, **kwargs):
    from distributed import Nanny

    with log_errors():
        with pristine_loop() as loop:
            scheduler_addr = scheduler_q.get()
            worker = Nanny(scheduler_addr, validate=True, **kwargs)
            loop.run_sync(lambda: worker._start(0))
            q.put(worker.address)
            try:
                loop.start()
            finally:
                loop.run_sync(worker._close)
                loop.close(all_fds=True)


@contextmanager
def check_active_rpc(loop, active_rpc_timeout=1):
    active_before = set(rpc.active)
    if active_before and not PY3:
        # On Python 2, try to avoid dangling comms before forking workers
        gc.collect()
        active_before = set(rpc.active)
    yield
    # Some streams can take a bit of time to notice their peer
    # has closed, and keep a coroutine (*) waiting for a CommClosedError
    # before calling close_rpc() after a CommClosedError.
    # This would happen especially if a non-localhost address is used,
    # as Nanny does.
    # (*) (example: gather_from_workers())

    def fail():
        pytest.fail("some RPCs left active by test: %s"
                    % (sorted(set(rpc.active) - active_before)))

    @gen.coroutine
    def wait():
        yield async_wait_for(lambda: len(set(rpc.active) - active_before) == 0,
                             timeout=active_rpc_timeout, fail_func=fail)

    loop.run_sync(wait)


@contextmanager
def cluster(nworkers=2, nanny=False, worker_kwargs={}, active_rpc_timeout=1,
            scheduler_kwargs={}):
    ws = weakref.WeakSet()
    old_globals = _globals.copy()

    for name, level in logging_levels.items():
        logging.getLogger(name).setLevel(level)

    enable_proctitle_on_children()

    with pristine_loop() as loop:
        with check_active_rpc(loop, active_rpc_timeout):
            if nanny:
                _run_worker = run_nanny
            else:
                _run_worker = run_worker

            # The scheduler queue will receive the scheduler's address
            scheduler_q = mp_context.Queue()

            # Launch scheduler
            scheduler = mp_context.Process(target=run_scheduler,
                                           args=(scheduler_q, nworkers + 1),
                                           kwargs=scheduler_kwargs)
            ws.add(scheduler)
            scheduler.daemon = True
            scheduler.start()

            # Launch workers
            workers = []
            for i in range(nworkers):
                q = mp_context.Queue()
                fn = '_test_worker-%s' % uuid.uuid4()
                kwargs = merge({'ncores': 1, 'local_dir': fn,
                                'memory_limit': TOTAL_MEMORY}, worker_kwargs)
                proc = mp_context.Process(target=_run_worker,
                                          args=(q, scheduler_q),
                                          kwargs=kwargs)
                ws.add(proc)
                workers.append({'proc': proc, 'queue': q, 'dir': fn})

            for worker in workers:
                worker['proc'].start()
            for worker in workers:
                worker['address'] = worker['queue'].get()

            saddr = scheduler_q.get()

            start = time()
            try:
                with rpc(saddr) as s:
                    while True:
                        ncores = loop.run_sync(s.ncores)
                        if len(ncores) == nworkers:
                            break
                        if time() - start > 5:
                            raise Exception("Timeout on cluster creation")

                # avoid sending processes down to function
                yield {'address': saddr}, [{'address': w['address'],
                                            'proc': weakref.ref(w['proc'])}
                                           for w in workers]
            finally:
                logger.debug("Closing out test cluster")

                loop.run_sync(lambda: disconnect_all([w['address'] for w in workers],
                                                     timeout=0.5))
                loop.run_sync(lambda: disconnect(saddr, timeout=0.5))

                scheduler.terminate()
                scheduler_q.close()
                scheduler_q._reader.close()
                scheduler_q._writer.close()

                for w in workers:
                    w['proc'].terminate()
                    w['queue'].close()
                    w['queue']._reader.close()
                    w['queue']._writer.close()

                scheduler.join(2)
                del scheduler
                for proc in [w['proc'] for w in workers]:
                    proc.join(timeout=2)

                with ignoring(UnboundLocalError):
                    del worker, w, proc
                del workers[:]

                for fn in glob('_test_worker-*'):
                    shutil.rmtree(fn)

                _globals.clear()
                _globals.update(old_globals)
    assert not ws


@gen.coroutine
def disconnect(addr, timeout=3):
    @gen.coroutine
    def do_disconnect():
        with ignoring(EnvironmentError, CommClosedError):
            with rpc(addr) as w:
                yield w.terminate(close=True)

    with ignoring(TimeoutError):
        yield gen.with_timeout(timedelta(seconds=timeout), do_disconnect())


@gen.coroutine
def disconnect_all(addresses, timeout=3):
    yield [disconnect(addr, timeout) for addr in addresses]


def slow(func):
    try:
        if not pytest.config.getoption("--runslow"):
            func = pytest.mark.skip("need --runslow option to run")(func)
    except AttributeError:
        # AttributeError: module 'pytest' has no attribute 'config'
        pass

    return nodebug(func)


def gen_test(timeout=10):
    """ Coroutine test

    @gen_test(timeout=5)
    def test_foo():
        yield ...  # use tornado coroutines
    """
    def _(func):
        def test_func():
            with pristine_loop() as loop:
                if iscoroutinefunction(func):
                    cor = func
                else:
                    cor = gen.coroutine(func)
                try:
                    loop.run_sync(cor, timeout=timeout)
                finally:
                    loop.stop()
        return test_func
    return _


from .scheduler import Scheduler
from .worker import Worker


@gen.coroutine
def start_cluster(ncores, scheduler_addr, loop, security=None,
                  Worker=Worker, scheduler_kwargs={}, worker_kwargs={}):
    s = Scheduler(loop=loop, validate=True, security=security,
                  **scheduler_kwargs)
    done = s.start(scheduler_addr)
    workers = [Worker(s.address, ncores=ncore[1], name=i, security=security,
                      loop=loop, validate=True,
                      **(merge(worker_kwargs, ncore[2])
                         if len(ncore) > 2
                         else worker_kwargs))
               for i, ncore in enumerate(ncores)]
    for w in workers:
        w.rpc = workers[0].rpc

    yield [w._start(ncore[0]) for ncore, w in zip(ncores, workers)]

    start = time()
    while (len(s.workers) < len(ncores) or
           any(comm.comm is None for comm in s.worker_comms.values())):
        yield gen.sleep(0.01)
        if time() - start > 5:
            yield [w._close(timeout=1) for w in workers]
            yield s.close(fast=True)
            raise Exception("Cluster creation timeout")
    raise gen.Return((s, workers))


@gen.coroutine
def end_cluster(s, workers):
    logger.debug("Closing out test cluster")

    @gen.coroutine
    def end_worker(w):
        with ignoring(TimeoutError, CommClosedError, EnvironmentError):
            yield w._close(report=False)

    yield [end_worker(w) for w in workers]
    yield s.close()  # wait until scheduler stops completely
    s.stop()


def iscoroutinefunction(f):
    if sys.version_info >= (3, 5) and inspect.iscoroutinefunction(f):
        return True
    return False


def gen_cluster(ncores=[('127.0.0.1', 1), ('127.0.0.1', 2)],
                scheduler='127.0.0.1', timeout=10, security=None,
                Worker=Worker, client=False, scheduler_kwargs={},
                worker_kwargs={}, active_rpc_timeout=1):
    from distributed import Client
    """ Coroutine test with small cluster

    @gen_cluster()
    def test_foo(scheduler, worker1, worker2):
        yield ...  # use tornado coroutines

    See also:
        start
        end
    """
    config['nanny-start-timeout'] = '5s'
    worker_kwargs = merge({'memory_limit': TOTAL_MEMORY, 'death_timeout': 5},
                          worker_kwargs)

    def _(func):
        if not iscoroutinefunction(func):
            func = gen.coroutine(func)

        def test_func():
            # Restore default logging levels
            # XXX use pytest hooks/fixtures instead?
            for name, level in logging_levels.items():
                logging.getLogger(name).setLevel(level)

            old_globals = _globals.copy()
            result = None
            workers = []

            with pristine_loop() as loop:
                with check_active_rpc(loop, active_rpc_timeout):
                    @gen.coroutine
                    def coro():
                        for i in range(5):
                            try:
                                s, ws = yield start_cluster(
                                    ncores, scheduler, loop, security=security,
                                    Worker=Worker, scheduler_kwargs=scheduler_kwargs,
                                    worker_kwargs=worker_kwargs)
                            except Exception as e:
                                logger.error("Failed to start gen_cluster, retryng", exc_info=True)
                            else:
                                break
                        workers[:] = ws
                        args = [s] + workers
                        if client:
                            c = yield Client(s.address, loop=loop, security=security,
                                             asynchronous=True)
                            args = [c] + args
                        try:
                            result = yield func(*args)
                            if s.validate:
                                s.validate_state()
                        finally:
                            if client:
                                yield c._close(fast=s.status == 'closed')
                            yield end_cluster(s, workers)
                            _globals.clear()
                            _globals.update(old_globals)

                        raise gen.Return(result)

                    result = loop.run_sync(coro, timeout=timeout)

            for w in workers:
                if getattr(w, 'data', None):
                    try:
                        w.data.clear()
                    except EnvironmentError:
                        # zict backends can fail if their storage directory
                        # was already removed
                        pass
                    del w.data
            DequeHandler.clear_all_instances()
            return result

        return test_func
    return _


def raises(func, exc=Exception):
    try:
        func()
        return False
    except exc:
        return True


def terminate_process(proc):
    if proc.poll() is None:
        if sys.platform.startswith('win'):
            proc.send_signal(signal.CTRL_BREAK_EVENT)
        else:
            proc.send_signal(signal.SIGINT)
        try:
            if sys.version_info[0] == 3:
                proc.wait(10)
            else:
                start = time()
                while proc.poll() is None and time() < start + 10:
                    sleep(0.02)
        finally:
            # Make sure we don't leave the process lingering around
            with ignoring(OSError):
                proc.kill()


@contextmanager
def popen(*args, **kwargs):
    kwargs['stdout'] = subprocess.PIPE
    kwargs['stderr'] = subprocess.PIPE
    if sys.platform.startswith('win'):
        # Allow using CTRL_C_EVENT / CTRL_BREAK_EVENT
        kwargs['creationflags'] = subprocess.CREATE_NEW_PROCESS_GROUP
    dump_stdout = False
    proc = subprocess.Popen(*args, **kwargs)
    try:
        yield proc
    except Exception:
        dump_stdout = True
        raise

    finally:
        try:
            terminate_process(proc)
        finally:
            # XXX Also dump stdout if return code != 0 ?
            out, err = proc.communicate()
            if dump_stdout:
                print('\n\nPrint from stderr\n  %s\n=================\n' % args[0][0])
                print(err.decode())

                print('\n\nPrint from stdout\n=================\n')
                print(out.decode())


def wait_for_port(address, timeout=5):
    assert isinstance(address, tuple)
    deadline = time() + timeout

    while True:
        timeout = deadline - time()
        if timeout < 0:
            raise RuntimeError("Failed to connect to %s" % (address,))
        try:
            sock = socket.create_connection(address, timeout=timeout)
        except EnvironmentError:
            pass
        else:
            sock.close()
            break


def wait_for(predicate, timeout, fail_func=None, period=0.001):
    deadline = time() + timeout
    while not predicate():
        sleep(period)
        if time() > deadline:
            if fail_func is not None:
                fail_func()
            pytest.fail("condition not reached until %s seconds" % (timeout,))


@gen.coroutine
def async_wait_for(predicate, timeout, fail_func=None, period=0.001):
    deadline = time() + timeout
    while not predicate():
        yield gen.sleep(period)
        if time() > deadline:
            if fail_func is not None:
                fail_func()
            pytest.fail("condition not reached until %s seconds" % (timeout,))


@memoize
def has_ipv6():
    """
    Return whether IPv6 is locally functional.  This doesn't guarantee IPv6
    is properly configured outside of localhost.
    """
    serv = cli = None
    try:
        serv = socket.socket(socket.AF_INET6, socket.SOCK_STREAM)
        serv.bind(('::', 0))
        serv.listen(5)
        cli = socket.create_connection(serv.getsockname()[:2])
    except EnvironmentError:
        return False
    else:
        return True
    finally:
        if cli is not None:
            cli.close()
        if serv is not None:
            serv.close()


if has_ipv6():
    def requires_ipv6(test_func):
        return test_func

else:
    requires_ipv6 = pytest.mark.skip("ipv6 required")


@gen.coroutine
def assert_can_connect(addr, timeout=None, connection_args=None):
    """
    Check that it is possible to connect to the distributed *addr*
    within the given *timeout*.
    """
    if timeout is None:
        timeout = 0.2
    comm = yield connect(addr, timeout=timeout,
                         connection_args=connection_args)
    comm.abort()


@gen.coroutine
def assert_cannot_connect(addr, timeout=None, connection_args=None):
    """
    Check that it is impossible to connect to the distributed *addr*
    within the given *timeout*.
    """
    if timeout is None:
        timeout = 0.2
    with pytest.raises(EnvironmentError):
        comm = yield connect(addr, timeout=timeout,
                             connection_args=connection_args)
        comm.abort()


@gen.coroutine
def assert_can_connect_from_everywhere_4_6(port, timeout=None, connection_args=None):
    """
    Check that the local *port* is reachable from all IPv4 and IPv6 addresses.
    """
    args = (timeout, connection_args)
    futures = [
        assert_can_connect('tcp://127.0.0.1:%d' % port, *args),
        assert_can_connect('tcp://%s:%d' % (get_ip(), port), *args),
    ]
    if has_ipv6():
        futures += [
            assert_can_connect('tcp://[::1]:%d' % port, *args),
            assert_can_connect('tcp://[%s]:%d' % (get_ipv6(), port), *args),
        ]
    yield futures


@gen.coroutine
def assert_can_connect_from_everywhere_4(port, timeout=None, connection_args=None):
    """
    Check that the local *port* is reachable from all IPv4 addresses.
    """
    args = (timeout, connection_args)
    futures = [
        assert_can_connect('tcp://127.0.0.1:%d' % port, *args),
        assert_can_connect('tcp://%s:%d' % (get_ip(), port), *args),
    ]
    if has_ipv6():
        futures += [
            assert_cannot_connect('tcp://[::1]:%d' % port, *args),
            assert_cannot_connect('tcp://[%s]:%d' % (get_ipv6(), port), *args),
        ]
    yield futures


@gen.coroutine
def assert_can_connect_locally_4(port, timeout=None, connection_args=None):
    """
    Check that the local *port* is only reachable from local IPv4 addresses.
    """
    args = (timeout, connection_args)
    futures = [
        assert_can_connect('tcp://127.0.0.1:%d' % port, *args),
    ]
    if get_ip() != '127.0.0.1':  # No outside IPv4 connectivity?
        futures += [
            assert_cannot_connect('tcp://%s:%d' % (get_ip(), port), *args),
        ]
    if has_ipv6():
        futures += [
            assert_cannot_connect('tcp://[::1]:%d' % port, *args),
            assert_cannot_connect('tcp://[%s]:%d' % (get_ipv6(), port), *args),
        ]
    yield futures


@gen.coroutine
def assert_can_connect_from_everywhere_6(port, timeout=None, connection_args=None):
    """
    Check that the local *port* is reachable from all IPv6 addresses.
    """
    assert has_ipv6()
    args = (timeout, connection_args)
    futures = [
        assert_cannot_connect('tcp://127.0.0.1:%d' % port, *args),
        assert_cannot_connect('tcp://%s:%d' % (get_ip(), port), *args),
        assert_can_connect('tcp://[::1]:%d' % port, *args),
        assert_can_connect('tcp://[%s]:%d' % (get_ipv6(), port), *args),
    ]
    yield futures


@gen.coroutine
def assert_can_connect_locally_6(port, timeout=None, connection_args=None):
    """
    Check that the local *port* is only reachable from local IPv6 addresses.
    """
    assert has_ipv6()
    args = (timeout, connection_args)
    futures = [
        assert_cannot_connect('tcp://127.0.0.1:%d' % port, *args),
        assert_cannot_connect('tcp://%s:%d' % (get_ip(), port), *args),
        assert_can_connect('tcp://[::1]:%d' % port, *args),
    ]
    if get_ipv6() != '::1':  # No outside IPv6 connectivity?
        futures += [
            assert_cannot_connect('tcp://[%s]:%d' % (get_ipv6(), port), *args),
        ]
    yield futures


@contextmanager
def captured_logger(logger, level=logging.INFO, propagate=None):
    """Capture output from the given Logger.
    """
    if isinstance(logger, str):
        logger = logging.getLogger(logger)
    orig_level = logger.level
    orig_handlers = logger.handlers[:]
    if propagate is not None:
        orig_propagate = logger.propagate
        logger.propagate = propagate
    sio = six.StringIO()
    logger.handlers[:] = [logging.StreamHandler(sio)]
    logger.setLevel(level)
    try:
        yield sio
    finally:
        logger.handlers[:] = orig_handlers
        logger.setLevel(orig_level)
        if propagate is not None:
            logger.propagate = orig_propagate


@contextmanager
def captured_handler(handler):
    """Capture output from the given logging.StreamHandler.
    """
    assert isinstance(handler, logging.StreamHandler)
    orig_stream = handler.stream
    handler.stream = six.StringIO()
    try:
        yield handler.stream
    finally:
        handler.stream = orig_stream


@contextmanager
def new_config(new_config):
    """
    Temporarily change configuration dictionary.
    """
    orig_config = config.copy()
    try:
        config.clear()
        config.update(new_config)
        initialize_logging(config)
        yield
    finally:
        config.clear()
        config.update(orig_config)
        initialize_logging(config)


@contextmanager
def new_config_file(c):
    """
    Temporarily change configuration file to match dictionary *c*.
    """
    import yaml
    old_file = os.environ.get('DASK_CONFIG')
    fd, path = tempfile.mkstemp(prefix='dask-config')
    try:
        with os.fdopen(fd, 'w') as f:
            f.write(yaml.dump(c))
        os.environ['DASK_CONFIG'] = path
        try:
            yield
        finally:
            if old_file:
                os.environ['DASK_CONFIG'] = old_file
            else:
                del os.environ['DASK_CONFIG']
    finally:
        os.remove(path)


certs_dir = os.path.abspath(os.path.join(os.path.dirname(__file__),
                                         'tests'))


def get_cert(filename):
    """
    Get the path to one of the test TLS certificates.
    """
    path = os.path.join(certs_dir, filename)
    assert os.path.exists(path), path
    return path


def tls_config():
    """
    A functional TLS configuration with our test certs.
    """
    ca_file = get_cert('tls-ca-cert.pem')
    keycert = get_cert('tls-key-cert.pem')

    c = {
        'tls': {
            'ca-file': ca_file,
            'client': {
                'cert': keycert,
            },
            'scheduler': {
                'cert': keycert,
            },
            'worker': {
                'cert': keycert,
            },
        },
    }
    return c


def tls_only_config():
    """
    A functional TLS configuration with our test certs, disallowing
    plain TCP communications.
    """
    c = tls_config()
    c['require-encryption'] = True
    return c


def tls_security():
    """
    A Security object with proper TLS configuration.
    """
    with new_config(tls_config()):
        sec = Security()
    return sec


def tls_only_security():
    """
    A Security object with proper TLS configuration and disallowing plain
    TCP communications.
    """
    with new_config(tls_only_config()):
        sec = Security()
    assert sec.require_encryption
    return sec


def get_server_ssl_context(certfile='tls-cert.pem', keyfile='tls-key.pem',
                           ca_file='tls-ca-cert.pem'):
    ctx = ssl.create_default_context(ssl.Purpose.CLIENT_AUTH,
                                     cafile=get_cert(ca_file))
    ctx.check_hostname = False
    ctx.verify_mode = ssl.CERT_REQUIRED
    ctx.load_cert_chain(get_cert(certfile), get_cert(keyfile))
    return ctx


def get_client_ssl_context(certfile='tls-cert.pem', keyfile='tls-key.pem',
                           ca_file='tls-ca-cert.pem'):
    ctx = ssl.create_default_context(ssl.Purpose.SERVER_AUTH,
                                     cafile=get_cert(ca_file))
    ctx.check_hostname = False
    ctx.verify_mode = ssl.CERT_REQUIRED
    ctx.load_cert_chain(get_cert(certfile), get_cert(keyfile))
    return ctx


def bump_rlimit(limit, desired):
    resource = pytest.importorskip('resource')
    try:
        soft, hard = resource.getrlimit(limit)
        if soft < desired:
            resource.setrlimit(limit,
                               (desired, max(hard, desired)))
    except Exception as e:
        pytest.skip("rlimit too low (%s) and can't be increased: %s"
                    % (soft, e))
