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import cStringIO as StringIO
import collections
import fcntl
import multiprocessing
import os
import select
import signal
import sys
import threading
import time
import unittest
import uuid

from tests import _loader
from tests import _result

# This number needs to be large enough to outpace output on stdout and stderr
# from the gRPC core, otherwise we could end up in a potential deadlock. This
# stems from the OS waiting on someone to clear a filled pipe buffer while the
# GIL is held from a write to stderr from gRPC core, but said someone is in
# Python code thus necessitating GIL acquisition.
_READ_BYTES = 2**20


class CapturePipe(object):
  """A context-manager pipe to redirect output to a byte array.

  Attributes:
    _redirect_fd (int): File descriptor of file to redirect writes from.
    _saved_fd (int): A copy of the original value of the redirected file
      descriptor.
    _read_thread (threading.Thread or None): Thread upon which reads through the
      pipe are performed. Only non-None when self is started.
    _read_fd (int or None): File descriptor of the read end of the redirect
      pipe. Only non-None when self is started.
    _write_fd (int or None): File descriptor of the write end of the redirect
      pipe. Only non-None when self is started.
    output (bytearray or None): Redirected output from writes to the redirected
      file descriptor. Only valid during and after self has started.
  """

  def __init__(self, fd):
    self._redirect_fd = fd
    self._saved_fd = os.dup(self._redirect_fd)
    self._read_thread = None
    self._read_fd = None
    self._write_fd = None
    self.output = None

  def start(self):
    """Start redirection of writes to the file descriptor."""
    self._read_fd, self._write_fd = os.pipe()
    os.dup2(self._write_fd, self._redirect_fd)
    flags = fcntl.fcntl(self._read_fd, fcntl.F_GETFL)
    fcntl.fcntl(self._read_fd, fcntl.F_SETFL, flags | os.O_NONBLOCK)
    self._read_thread = threading.Thread(target=self._read)
    # If the user wants to exit from the Python program and hits ctrl-C and the
    # read thread is somehow deadlocked with something else, the Python code may
    # refuse to exit. This prevents that by making the read thread second-class.
    self._read_thread.daemon = True
    self._read_thread.start()

  def stop(self):
    """Stop redirection of writes to the file descriptor."""
    os.close(self._write_fd)
    os.dup2(self._saved_fd, self._redirect_fd)  # auto-close self._redirect_fd
    self._read_thread.join()
    self._read_thread = None
    # we waited for the read thread to finish, so _read_fd has been read and we
    # can close it.
    os.close(self._read_fd)

  def _read(self):
    """Read-thread target for self."""
    self.output = bytearray()
    while True:
      select.select([self._read_fd], [], [])
      read_bytes = os.read(self._read_fd, _READ_BYTES)
      if read_bytes:
        self.output.extend(read_bytes)
      else:
        break

  def write_bypass(self, value):
    """Bypass the redirection and write directly to the original file.

    Arguments:
      value (str): What to write to the original file.
    """
    if self._saved_fd is None:
      os.write(self._redirect_fd, value)
    else:
      os.write(self._saved_fd, value)

  def __enter__(self):
    self.start()
    return self

  def __exit__(self, type, value, traceback):
    self.stop()

  def close(self):
    """Close any resources used by self not closed by stop()."""
    os.close(self._saved_fd)


class AugmentedCase(collections.namedtuple('AugmentedCase', [
    'case', 'id'])):
  """A test case with a guaranteed unique externally specified identifier.

  Attributes:
    case (unittest.TestCase): TestCase we're decorating with an additional
      identifier.
    id (object): Any identifier that may be considered 'unique' for testing
      purposes.
  """

  def __new__(cls, case, id=None):
    if id is None:
      id = uuid.uuid4()
    return super(cls, AugmentedCase).__new__(cls, case, id)


class Runner(object):

  def run(self, suite):
    """See setuptools' test_runner setup argument for information."""
    # only run test cases with id starting with given prefix
    testcase_filter = os.getenv('GRPC_PYTHON_TESTRUNNER_FILTER')
    filtered_cases = []
    for case in _loader.iterate_suite_cases(suite):
      if not testcase_filter or case.id().startswith(testcase_filter):
        filtered_cases.append(case)

    # Ensure that every test case has no collision with any other test case in
    # the augmented results.
    augmented_cases = [AugmentedCase(case, uuid.uuid4())
                       for case in filtered_cases]
    case_id_by_case = dict((augmented_case.case, augmented_case.id)
                           for augmented_case in augmented_cases)
    result_out = StringIO.StringIO()
    result = _result.TerminalResult(
        result_out, id_map=lambda case: case_id_by_case[case])
    stdout_pipe = CapturePipe(sys.stdout.fileno())
    stderr_pipe = CapturePipe(sys.stderr.fileno())
    kill_flag = [False]

    def sigint_handler(signal_number, frame):
      if signal_number == signal.SIGINT:
        kill_flag[0] = True  # Python 2.7 not having 'local'... :-(
      signal.signal(signal_number, signal.SIG_DFL)

    def fault_handler(signal_number, frame):
      stdout_pipe.write_bypass(
          'Received fault signal {}\nstdout:\n{}\n\nstderr:{}\n'
          .format(signal_number, stdout_pipe.output, stderr_pipe.output))
      os._exit(1)

    def check_kill_self():
      if kill_flag[0]:
        stdout_pipe.write_bypass('Stopping tests short...')
        result.stopTestRun()
        stdout_pipe.write_bypass(result_out.getvalue())
        stdout_pipe.write_bypass(
            '\ninterrupted stdout:\n{}\n'.format(stdout_pipe.output))
        stderr_pipe.write_bypass(
            '\ninterrupted stderr:\n{}\n'.format(stderr_pipe.output))
        os._exit(1)
    signal.signal(signal.SIGINT, sigint_handler)
    signal.signal(signal.SIGSEGV, fault_handler)
    signal.signal(signal.SIGBUS, fault_handler)
    signal.signal(signal.SIGABRT, fault_handler)
    signal.signal(signal.SIGFPE, fault_handler)
    signal.signal(signal.SIGILL, fault_handler)
    # Sometimes output will lag after a test has successfully finished; we
    # ignore such writes to our pipes.
    signal.signal(signal.SIGPIPE, signal.SIG_IGN)

    # Run the tests
    result.startTestRun()
    for augmented_case in augmented_cases:
      sys.stdout.write('Running       {}\n'.format(augmented_case.case.id()))
      sys.stdout.flush()
      case_thread = threading.Thread(
          target=augmented_case.case.run, args=(result,))
      try:
        with stdout_pipe, stderr_pipe:
          case_thread.start()
          while case_thread.is_alive():
            check_kill_self()
            time.sleep(0)
          case_thread.join()
      except:
        # re-raise the exception after forcing the with-block to end
        raise
      result.set_output(
          augmented_case.case, stdout_pipe.output, stderr_pipe.output)
      sys.stdout.write(result_out.getvalue())
      sys.stdout.flush()
      result_out.truncate(0)
      check_kill_self()
    result.stopTestRun()
    stdout_pipe.close()
    stderr_pipe.close()

    # Report results
    sys.stdout.write(result_out.getvalue())
    sys.stdout.flush()
    signal.signal(signal.SIGINT, signal.SIG_DFL)
    with open('report.xml', 'w') as report_xml_file:
      _result.jenkins_junit_xml(result).write(report_xml_file)
    return result