text: # -*- coding: utf-8 -*-
  
  import locale
  import os
  import struct
  from subprocess import Popen, PIPE
  import sys
  import threading
  import time
  import signal
  
  from .util import six
  
  # Import some platform-specific things at top level so they can be mocked for
  # tests.
  try:
      import pty
  except ImportError:
      pty = None
  try:
      import fcntl
  except ImportError:
      fcntl = None
  try:
      import termios
  except ImportError:
      termios = None
  
  from .exceptions import (
      UnexpectedExit,
      Failure,
      ThreadException,
      WatcherError,
      SubprocessPipeError,
      CommandTimedOut,
  )
  from .terminals import (
      WINDOWS,
      pty_size,
      character_buffered,
      ready_for_reading,
      bytes_to_read,
  )
  from .util import has_fileno, isatty, ExceptionHandlingThread, encode_output
  
  
  class Runner(object):
      """
      Partially-abstract core command-running API.
  
      This class is not usable by itself and must be subclassed, implementing a
      number of methods such as `start`, `wait` and `returncode`. For a subclass
      implementation example, see the source code for `.Local`.
  
      .. versionadded:: 1.0
      """
  
      read_chunk_size = 1000
      input_sleep = 0.01
  
      def __init__(self, context):
          """
          Create a new runner with a handle on some `.Context`.
  
          :param context:
              a `.Context` instance, used to transmit default options and provide
              access to other contextualized information (e.g. a remote-oriented
              `.Runner` might want a `.Context` subclass holding info about
              hostnames and ports.)
  
              .. note::
                  The `.Context` given to `.Runner` instances **must** contain
                  default config values for the `.Runner` class in question. At a
                  minimum, this means values for each of the default
                  `.Runner.run` keyword arguments such as ``echo`` and ``warn``.
  
          :raises exceptions.ValueError:
              if not all expected default values are found in ``context``.
          """
          #: The `.Context` given to the same-named argument of `__init__`.
          self.context = context
          #: A `threading.Event` signaling program completion.
          #:
          #: Typically set after `wait` returns. Some IO mechanisms rely on this
          #: to know when to exit an infinite read loop.
          self.program_finished = threading.Event()
          # I wish Sphinx would organize all class/instance attrs in the same
          # place. If I don't do this here, it goes 'class vars -> __init__
          # docstring -> instance vars' :( TODO: consider just merging class and
          # __init__ docstrings, though that's annoying too.
          #: How many bytes (at maximum) to read per iteration of stream reads.
          self.read_chunk_size = self.__class__.read_chunk_size
          # Ditto re: declaring this in 2 places for doc reasons.
          #: How many seconds to sleep on each iteration of the stdin read loop
          #: and other otherwise-fast loops.
          self.input_sleep = self.__class__.input_sleep
          #: Whether pty fallback warning has been emitted.
          self.warned_about_pty_fallback = False
          #: A list of `.StreamWatcher` instances for use by `respond`. Is filled
          #: in at runtime by `run`.
          self.watchers = []
          self._timer = None
  
      def run(self, command, **kwargs):
          """
          Execute ``command``, returning an instance of `Result`.
  
          .. note::
              All kwargs will default to the values found in this instance's
              `~.Runner.context` attribute, specifically in its configuration's
              ``run`` subtree (e.g. ``run.echo`` provides the default value for
              the ``echo`` keyword, etc). The base default values are described
              in the parameter list below.
  
          :param str command: The shell command to execute.
  
          :param str shell:
              Which shell binary to use. Default: ``/bin/bash`` (on Unix;
              ``COMSPEC`` or ``cmd.exe`` on Windows.)
  
          :param bool warn:
              Whether to warn and continue, instead of raising
              `.UnexpectedExit`, when the executed command exits with a
              nonzero status. Default: ``False``.
  
              .. note::
                  This setting has no effect on exceptions, which will still be
                  raised, typically bundled in `.ThreadException` objects if they
                  were raised by the IO worker threads.
  
                  Similarly, `.WatcherError` exceptions raised by
                  `.StreamWatcher` instances will also ignore this setting, and
                  will usually be bundled inside `.Failure` objects (in order to
                  preserve the execution context).
  
                  Ditto `.CommandTimedOut` - basically, anything that prevents a
                  command from actually getting to "exited with an exit code"
                  ignores this flag.
  
          :param hide:
              Allows the caller to disable ``run``'s default behavior of copying
              the subprocess' stdout and stderr to the controlling terminal.
              Specify ``hide='out'`` (or ``'stdout'``) to hide only the stdout
              stream, ``hide='err'`` (or ``'stderr'``) to hide only stderr, or
              ``hide='both'`` (or ``True``) to hide both streams.
  
              The default value is ``None``, meaning to print everything;
              ``False`` will also disable hiding.
  
              .. note::
                  Stdout and stderr are always captured and stored in the
                  ``Result`` object, regardless of ``hide``'s value.
  
              .. note::
                  ``hide=True`` will also override ``echo=True`` if both are
                  given (either as kwargs or via config/CLI).
  
          :param bool pty:
              By default, ``run`` connects directly to the invoked process and
              reads its stdout/stderr streams. Some programs will buffer (or even
              behave) differently in this situation compared to using an actual
              terminal or pseudoterminal (pty). To use a pty instead of the
              default behavior, specify ``pty=True``.
  
              .. warning::
                  Due to their nature, ptys have a single output stream, so the
                  ability to tell stdout apart from stderr is **not possible**
                  when ``pty=True``. As such, all output will appear on
                  ``out_stream`` (see below) and be captured into the ``stdout``
                  result attribute. ``err_stream`` and ``stderr`` will always be
                  empty when ``pty=True``.
  
          :param bool fallback:
              Controls auto-fallback behavior re: problems offering a pty when
              ``pty=True``. Whether this has any effect depends on the specific
              `Runner` subclass being invoked. Default: ``True``.
  
          :param bool echo:
              Controls whether `.run` prints the command string to local stdout
              prior to executing it. Default: ``False``.
  
              .. note::
                  ``hide=True`` will override ``echo=True`` if both are given.
  
          :param dict env:
              By default, subprocesses receive a copy of Invoke's own environment
              (i.e. ``os.environ``). Supply a dict here to update that child
              environment.
  
              For example, ``run('command', env={'PYTHONPATH':
              '/some/virtual/env/maybe'})`` would modify the ``PYTHONPATH`` env
              var, with the rest of the child's env looking identical to the
              parent.
  
              .. seealso:: ``replace_env`` for changing 'update' to 'replace'.
  
          :param bool replace_env:
              When ``True``, causes the subprocess to receive the dictionary
              given to ``env`` as its entire shell environment, instead of
              updating a copy of ``os.environ`` (which is the default behavior).
              Default: ``False``.
  
          :param str encoding:
              Override auto-detection of which encoding the subprocess is using
              for its stdout/stderr streams (which defaults to the return value
              of `default_encoding`).
  
          :param out_stream:
              A file-like stream object to which the subprocess' standard output
              should be written. If ``None`` (the default), ``sys.stdout`` will
              be used.
  
          :param err_stream:
              Same as ``out_stream``, except for standard error, and defaulting
              to ``sys.stderr``.
  
          :param in_stream:
              A file-like stream object to used as the subprocess' standard
              input. If ``None`` (the default), ``sys.stdin`` will be used.
  
              If ``False``, will disable stdin mirroring entirely (though other
              functionality which writes to the subprocess' stdin, such as
              autoresponding, will still function.) Disabling stdin mirroring can
              help when ``sys.stdin`` is a misbehaving non-stream object, such as
              under test harnesses or headless command runners.
  
          :param watchers:
              A list of `.StreamWatcher` instances which will be used to scan the
              program's ``stdout`` or ``stderr`` and may write into its ``stdin``
              (typically ``str`` or ``bytes`` objects depending on Python
              version) in response to patterns or other heuristics.
  
              See :doc:`/concepts/watchers` for details on this functionality.
  
              Default: ``[]``.
  
          :param bool echo_stdin:
              Whether to write data from ``in_stream`` back to ``out_stream``.
  
              In other words, in normal interactive usage, this parameter
              controls whether Invoke mirrors what you type back to your
              terminal.
  
              By default (when ``None``), this behavior is triggered by the
              following:
  
                  * Not using a pty to run the subcommand (i.e. ``pty=False``),
                    as ptys natively echo stdin to stdout on their own;
                  * And when the controlling terminal of Invoke itself (as per
                    ``in_stream``) appears to be a valid terminal device or TTY.
                    (Specifically, when `~invoke.util.isatty` yields a ``True``
                    result when given ``in_stream``.)
  
                    .. note::
                        This property tends to be ``False`` when piping another
                        program's output into an Invoke session, or when running
                        Invoke within another program (e.g. running Invoke from
                        itself).
  
              If both of those properties are true, echoing will occur; if either
              is false, no echoing will be performed.
  
              When not ``None``, this parameter will override that auto-detection
              and force, or disable, echoing.
  
          :param timeout:
              Cause the runner to submit an interrupt to the subprocess and raise
              `CommandTimedOut`, if the command takes longer than ``timeout``
              seconds to execute. Defaults to ``None``, meaning no timeout.
  
              .. versionadded:: 1.3
  
          :returns:
              `Result`, or a subclass thereof.
  
          :raises:
              `.UnexpectedExit`, if the command exited nonzero and
              ``warn`` was ``False``.
  
          :raises:
              `.Failure`, if the command didn't even exit cleanly, e.g. if a
              `.StreamWatcher` raised `.WatcherError`.
  
          :raises:
              `.ThreadException` (if the background I/O threads encountered
              exceptions other than `.WatcherError`).
  
          .. versionadded:: 1.0
          """
          try:
              return self._run_body(command, **kwargs)
          finally:
              self.stop()
              self.stop_timer()
  
      def _run_body(self, command, **kwargs):
          # Normalize kwargs w/ config
          opts, out_stream, err_stream, in_stream = self._run_opts(kwargs)
          shell = opts["shell"]
          # Environment setup
          env = self.generate_env(opts["env"], opts["replace_env"])
          # Echo running command
          if opts["echo"]:
              print("\033[1;37m{}\033[0m".format(command))
          # If dry-run, stop here.
          if opts["dry"]:
              return self.generate_result(
                  command=command,
                  stdout="",
                  stderr="",
                  exited=0,
                  pty=self.using_pty,
              )
          # Start executing the actual command (runs in background)
          self.start(command, shell, env)
          self.start_timer(opts["timeout"])
          # Arrive at final encoding if neither config nor kwargs had one
          self.encoding = opts["encoding"] or self.default_encoding()
          # Set up IO thread parameters (format - body_func: {kwargs})
          stdout, stderr = [], []
          thread_args = {
              self.handle_stdout: {
                  "buffer_": stdout,
                  "hide": "stdout" in opts["hide"],
                  "output": out_stream,
              }
          }
          # After opt processing above, in_stream will be a real stream obj or
          # False, so we can truth-test it. We don't even create a stdin-handling
          # thread if it's False, meaning user indicated stdin is nonexistent or
          # problematic.
          if in_stream:
              thread_args[self.handle_stdin] = {
                  "input_": in_stream,
                  "output": out_stream,
                  "echo": opts["echo_stdin"],
              }
          if not self.using_pty:
              thread_args[self.handle_stderr] = {
                  "buffer_": stderr,
                  "hide": "stderr" in opts["hide"],
                  "output": err_stream,
              }
          # Kick off IO threads
          self.threads = {}
          exceptions = []
          for target, kwargs in six.iteritems(thread_args):
              t = ExceptionHandlingThread(target=target, kwargs=kwargs)
              self.threads[target] = t
              t.start()
          # Wait for completion, then tie things off & obtain result
          # And make sure we perform that tying off even if things asplode.
          exception = None
          while True:
              try:
                  self.wait()
                  break  # done waiting!
              # NOTE: we handle all this now instead of at
              # actual-exception-handling time because otherwise the stdout/err
              # reader threads may block until the subprocess exits.
              # TODO: honor other signals sent to our own process and transmit
              # them to the subprocess before handling 'normally'.
              except KeyboardInterrupt as e:
                  self.send_interrupt(e)
                  # NOTE: no break; we want to return to self.wait() since we
                  # can't know if subprocess is actually terminating due to this
                  # or not (think REPLs-within-shells, editors, other interactive
                  # use cases)
              except BaseException as e:  # Want to handle SystemExit etc still
                  # Store exception for post-shutdown reraise
                  exception = e
                  # Break out of return-to-wait() loop - we want to shut down
                  break
          # Inform stdin-mirroring worker to stop its eternal looping
          self.program_finished.set()
          # Join threads, setting a timeout if necessary
          for target, thread in six.iteritems(self.threads):
              thread.join(self._thread_join_timeout(target))
              e = thread.exception()
              if e is not None:
                  exceptions.append(e)
          # If we got a main-thread exception while wait()ing, raise it now that
          # we've closed our worker threads.
          if exception is not None:
              raise exception
          # Strip out WatcherError from any thread exceptions; they are bundled
          # into Failure handling at the end.
          watcher_errors = []
          thread_exceptions = []
          for exception in exceptions:
              real = exception.value
              if isinstance(real, WatcherError):
                  watcher_errors.append(real)
              else:
                  thread_exceptions.append(exception)
          # If any exceptions appeared inside the threads, raise them now as an
          # aggregate exception object.
          if thread_exceptions:
              raise ThreadException(thread_exceptions)
          # At this point, we had enough success that we want to be returning or
          # raising detailed info about our execution; so we generate a Result.
          stdout = "".join(stdout)
          stderr = "".join(stderr)
          if WINDOWS:
              # "Universal newlines" - replace all standard forms of
              # newline with \n. This is not technically Windows related
              # (\r as newline is an old Mac convention) but we only apply
              # the translation for Windows as that's the only platform
              # it is likely to matter for these days.
              stdout = stdout.replace("\r\n", "\n").replace("\r", "\n")
              stderr = stderr.replace("\r\n", "\n").replace("\r", "\n")
          # Get return/exit code, unless there were WatcherErrors to handle.
          # NOTE: In that case, returncode() may block waiting on the process
          # (which may be waiting for user input). Since most WatcherError
          # situations lack a useful exit code anyways, skipping this doesn't
          # really hurt any.
          exited = None if watcher_errors else self.returncode()
          # Obtain actual result
          result = self.generate_result(
              command=command,
              shell=shell,
              env=env,
              stdout=stdout,
              stderr=stderr,
              exited=exited,
              pty=self.using_pty,
              hide=opts["hide"],
              encoding=self.encoding,
          )
          # Any presence of WatcherError from the threads indicates a watcher was
          # upset and aborted execution; make a generic Failure out of it and
          # raise that.
          if watcher_errors:
              # TODO: ambiguity exists if we somehow get WatcherError in *both*
              # threads...as unlikely as that would normally be.
              raise Failure(result, reason=watcher_errors[0])
          # If a timeout was requested and the subprocess did time out, shout.
          timeout = opts["timeout"]
          if timeout is not None and self.timed_out:
              raise CommandTimedOut(result, timeout=timeout)
          if not (result or opts["warn"]):
              raise UnexpectedExit(result)
          return result
  
      def _run_opts(self, kwargs):
          """
          Unify `run` kwargs with config options to arrive at local options.
  
          :returns:
              Four-tuple of ``(opts_dict, stdout_stream, stderr_stream,
              stdin_stream)``.
          """
          opts = {}
          for key, value in six.iteritems(self.context.config.run):
              runtime = kwargs.pop(key, None)
              opts[key] = value if runtime is None else runtime
          # Pull in command execution timeout, which stores config elsewhere,
          # but only use it if it's actually set (backwards compat)
          config_timeout = self.context.config.timeouts.command
          opts["timeout"] = kwargs.pop("timeout", config_timeout)
          # Handle invalid kwarg keys (anything left in kwargs).
          # Act like a normal function would, i.e. TypeError
          if kwargs:
              err = "run() got an unexpected keyword argument '{}'"
              raise TypeError(err.format(list(kwargs.keys())[0]))
          # If hide was True, turn off echoing
          if opts["hide"] is True:
              opts["echo"] = False
          # Conversely, ensure echoing is always on when dry-running
          if opts["dry"] is True:
              opts["echo"] = True
          # Then normalize 'hide' from one of the various valid input values,
          # into a stream-names tuple.
          opts["hide"] = normalize_hide(opts["hide"])
          # Derive stream objects
          out_stream = opts["out_stream"]
          if out_stream is None:
              out_stream = sys.stdout
          err_stream = opts["err_stream"]
          if err_stream is None:
              err_stream = sys.stderr
          in_stream = opts["in_stream"]
          if in_stream is None:
              in_stream = sys.stdin
          # Determine pty or no
          self.using_pty = self.should_use_pty(opts["pty"], opts["fallback"])
          if opts["watchers"]:
              self.watchers = opts["watchers"]
          return opts, out_stream, err_stream, in_stream
  
      def _thread_join_timeout(self, target):
          # Add a timeout to out/err thread joins when it looks like they're not
          # dead but their counterpart is dead; this indicates issue #351 (fixed
          # by #432) where the subproc may hang because its stdout (or stderr) is
          # no longer being consumed by the dead thread (and a pipe is filling
          # up.) In that case, the non-dead thread is likely to block forever on
          # a `recv` unless we add this timeout.
          if target == self.handle_stdin:
              return None
          opposite = self.handle_stderr
          if target == self.handle_stderr:
              opposite = self.handle_stdout
          if opposite in self.threads and self.threads[opposite].is_dead:
              return 1
          return None
  
      def generate_result(self, **kwargs):
          """
          Create & return a suitable `Result` instance from the given ``kwargs``.
  
          Subclasses may wish to override this in order to manipulate things or
          generate a `Result` subclass (e.g. ones containing additional metadata
          besides the default).
  
          .. versionadded:: 1.0
          """
          return Result(**kwargs)
  
      def read_proc_output(self, reader):
          """
          Iteratively read & decode bytes from a subprocess' out/err stream.
  
          :param reader:
              A literal reader function/partial, wrapping the actual stream
              object in question, which takes a number of bytes to read, and
              returns that many bytes (or ``None``).
  
              ``reader`` should be a reference to either `read_proc_stdout` or
              `read_proc_stderr`, which perform the actual, platform/library
              specific read calls.
  
          :returns:
              A generator yielding Unicode strings (`unicode` on Python 2; `str`
              on Python 3).
  
              Specifically, each resulting string is the result of decoding
              `read_chunk_size` bytes read from the subprocess' out/err stream.
  
          .. versionadded:: 1.0
          """
          # NOTE: Typically, reading from any stdout/err (local, remote or
          # otherwise) can be thought of as "read until you get nothing back".
          # This is preferable over "wait until an out-of-band signal claims the
          # process is done running" because sometimes that signal will appear
          # before we've actually read all the data in the stream (i.e.: a race
          # condition).
          while True:
              data = reader(self.read_chunk_size)
              if not data:
                  break
              yield self.decode(data)
  
      def write_our_output(self, stream, string):
          """
          Write ``string`` to ``stream``.
  
          Also calls ``.flush()`` on ``stream`` to ensure that real terminal
          streams don't buffer.
  
          :param stream:
              A file-like stream object, mapping to the ``out_stream`` or
              ``err_stream`` parameters of `run`.
  
          :param string: A Unicode string object.
  
          :returns: ``None``.
  
          .. versionadded:: 1.0
          """
          stream.write(encode_output(string, self.encoding))
          stream.flush()
  
      def _handle_output(self, buffer_, hide, output, reader):
          # TODO: store un-decoded/raw bytes somewhere as well...
          for data in self.read_proc_output(reader):
              # Echo to local stdout if necessary
              # TODO: should we rephrase this as "if you want to hide, give me a
              # dummy output stream, e.g. something like /dev/null"? Otherwise, a
              # combo of 'hide=stdout' + 'here is an explicit out_stream' means
              # out_stream is never written to, and that seems...odd.
              if not hide:
                  self.write_our_output(stream=output, string=data)
              # Store in shared buffer so main thread can do things with the
              # result after execution completes.
              # NOTE: this is threadsafe insofar as no reading occurs until after
              # the thread is join()'d.
              buffer_.append(data)
              # Run our specific buffer through the autoresponder framework
              self.respond(buffer_)
  
      def handle_stdout(self, buffer_, hide, output):
          """
          Read process' stdout, storing into a buffer & printing/parsing.
  
          Intended for use as a thread target. Only terminates when all stdout
          from the subprocess has been read.
  
          :param buffer_: The capture buffer shared with the main thread.
          :param bool hide: Whether or not to replay data into ``output``.
          :param output:
              Output stream (file-like object) to write data into when not
              hiding.
  
          :returns: ``None``.
  
          .. versionadded:: 1.0
          """
          self._handle_output(
              buffer_, hide, output, reader=self.read_proc_stdout
          )
  
      def handle_stderr(self, buffer_, hide, output):
          """
          Read process' stderr, storing into a buffer & printing/parsing.
  
          Identical to `handle_stdout` except for the stream read from; see its
          docstring for API details.
  
          .. versionadded:: 1.0
          """
          self._handle_output(
              buffer_, hide, output, reader=self.read_proc_stderr
          )
  
      def read_our_stdin(self, input_):
          """
          Read & decode bytes from a local stdin stream.
  
          :param input_:
              Actual stream object to read from. Maps to ``in_stream`` in `run`,
              so will often be ``sys.stdin``, but might be any stream-like
              object.
  
          :returns:
              A Unicode string, the result of decoding the read bytes (this might
              be the empty string if the pipe has closed/reached EOF); or
              ``None`` if stdin wasn't ready for reading yet.
  
          .. versionadded:: 1.0
          """
          # TODO: consider moving the character_buffered contextmanager call in
          # here? Downside is it would be flipping those switches for every byte
          # read instead of once per session, which could be costly (?).
          bytes_ = None
          if ready_for_reading(input_):
              bytes_ = input_.read(bytes_to_read(input_))
              # Decode if it appears to be binary-type. (From real terminal
              # streams, usually yes; from file-like objects, often no.)
              if bytes_ and isinstance(bytes_, six.binary_type):
                  # TODO: will decoding 1 byte at a time break multibyte
                  # character encodings? How to square interactivity with that?
                  bytes_ = self.decode(bytes_)
          return bytes_
  
      def handle_stdin(self, input_, output, echo):
          """
          Read local stdin, copying into process' stdin as necessary.
  
          Intended for use as a thread target.
  
          .. note::
              Because real terminal stdin streams have no well-defined "end", if
              such a stream is detected (based on existence of a callable
              ``.fileno()``) this method will wait until `program_finished` is
              set, before terminating.
  
              When the stream doesn't appear to be from a terminal, the same
              semantics as `handle_stdout` are used - the stream is simply
              ``read()`` from until it returns an empty value.
  
          :param input_: Stream (file-like object) from which to read.
          :param output: Stream (file-like object) to which echoing may occur.
          :param bool echo: User override option for stdin-stdout echoing.
  
          :returns: ``None``.
  
          .. versionadded:: 1.0
          """
          # TODO: reinstate lock/whatever thread logic from fab v1 which prevents
          # reading from stdin while other parts of the code are prompting for
          # runtime passwords? (search for 'input_enabled')
          # TODO: fabric#1339 is strongly related to this, if it's not literally
          # exposing some regression in Fabric 1.x itself.
          closed_stdin = False
          with character_buffered(input_):
              while True:
                  data = self.read_our_stdin(input_)
                  if data:
                      # Mirror what we just read to process' stdin.
                      # We perform an encode so Python 3 gets bytes (streams +
                      # str's in Python 3 == no bueno) but skip the decode step,
                      # since there's presumably no need (nobody's interacting
                      # with this data programmatically).
                      self.write_proc_stdin(data)
                      # Also echo it back to local stdout (or whatever
                      # out_stream is set to) when necessary.
                      if echo is None:
                          echo = self.should_echo_stdin(input_, output)
                      if echo:
                          self.write_our_output(stream=output, string=data)
                  # Empty string/char/byte != None. Can't just use 'else' here.
                  elif data is not None:
                      # When reading from file-like objects that aren't "real"
                      # terminal streams, an empty byte signals EOF.
                      if not self.using_pty and not closed_stdin:
                          self.close_proc_stdin()
                          closed_stdin = True
                  # Dual all-done signals: program being executed is done
                  # running, *and* we don't seem to be reading anything out of
                  # stdin. (NOTE: If we only test the former, we may encounter
                  # race conditions re: unread stdin.)
                  if self.program_finished.is_set() and not data:
                      break
                  # Take a nap so we're not chewing CPU.
                  time.sleep(self.input_sleep)
  
      def should_echo_stdin(self, input_, output):
          """
          Determine whether data read from ``input_`` should echo to ``output``.
  
          Used by `handle_stdin`; tests attributes of ``input_`` and ``output``.
  
          :param input_: Input stream (file-like object).
          :param output: Output stream (file-like object).
          :returns: A ``bool``.
  
          .. versionadded:: 1.0
          """
          return (not self.using_pty) and isatty(input_)
  
      def respond(self, buffer_):
          """
          Write to the program's stdin in response to patterns in ``buffer_``.
  
          The patterns and responses are driven by the `.StreamWatcher` instances
          from the ``watchers`` kwarg of `run` - see :doc:`/concepts/watchers`
          for a conceptual overview.
  
          :param buffer:
              The capture buffer for this thread's particular IO stream.
  
          :returns: ``None``.
  
          .. versionadded:: 1.0
          """
          # Join buffer contents into a single string; without this,
          # StreamWatcher subclasses can't do things like iteratively scan for
          # pattern matches.
          # NOTE: using string.join should be "efficient enough" for now, re:
          # speed and memory use. Should that become false, consider using
          # StringIO or cStringIO (tho the latter doesn't do Unicode well?) which
          # is apparently even more efficient.
          stream = u"".join(buffer_)
          for watcher in self.watchers:
              for response in watcher.submit(stream):
                  self.write_proc_stdin(response)
  
      def generate_env(self, env, replace_env):
          """
          Return a suitable environment dict based on user input & behavior.
  
          :param dict env: Dict supplying overrides or full env, depending.
          :param bool replace_env:
              Whether ``env`` updates, or is used in place of, the value of
              `os.environ`.
  
          :returns: A dictionary of shell environment vars.
  
          .. versionadded:: 1.0
          """
          return env if replace_env else dict(os.environ, **env)
  
      def should_use_pty(self, pty, fallback):
          """
          Should execution attempt to use a pseudo-terminal?
  
          :param bool pty:
              Whether the user explicitly asked for a pty.
          :param bool fallback:
              Whether falling back to non-pty execution should be allowed, in
              situations where ``pty=True`` but a pty could not be allocated.
  
          .. versionadded:: 1.0
          """
          # NOTE: fallback not used: no falling back implemented by default.
          return pty
  
      @property
      def has_dead_threads(self):
          """
          Detect whether any IO threads appear to have terminated unexpectedly.
  
          Used during process-completion waiting (in `wait`) to ensure we don't
          deadlock our child process if our IO processing threads have
          errored/died.
  
          :returns:
              ``True`` if any threads appear to have terminated with an
              exception, ``False`` otherwise.
  
          .. versionadded:: 1.0
          """
          return any(x.is_dead for x in self.threads.values())
  
      def wait(self):
          """
          Block until the running command appears to have exited.
  
          :returns: ``None``.
  
          .. versionadded:: 1.0
          """
          while True:
              proc_finished = self.process_is_finished
              dead_threads = self.has_dead_threads
              if proc_finished or dead_threads:
                  break
              time.sleep(self.input_sleep)
  
      def write_proc_stdin(self, data):
          """
          Write encoded ``data`` to the running process' stdin.
  
          :param data: A Unicode string.
  
          :returns: ``None``.
  
          .. versionadded:: 1.0
          """
          # Encode always, then request implementing subclass to perform the
          # actual write to subprocess' stdin.
          self._write_proc_stdin(data.encode(self.encoding))
  
      def decode(self, data):
          """
          Decode some ``data`` bytes, returning Unicode.
  
          .. versionadded:: 1.0
          """
          # NOTE: yes, this is a 1-liner. The point is to make it much harder to
          # forget to use 'replace' when decoding :)
          return data.decode(self.encoding, "replace")
  
      @property
      def process_is_finished(self):
          """
          Determine whether our subprocess has terminated.
  
          .. note::
              The implementation of this method should be nonblocking, as it is
              used within a query/poll loop.
  
          :returns:
              ``True`` if the subprocess has finished running, ``False``
              otherwise.
  
          .. versionadded:: 1.0
          """
          raise NotImplementedError
  
      def start(self, command, shell, env):
          """
          Initiate execution of ``command`` (via ``shell``, with ``env``).
  
          Typically this means use of a forked subprocess or requesting start of
          execution on a remote system.
  
          In most cases, this method will also set subclass-specific member
          variables used in other methods such as `wait` and/or `returncode`.
  
          :param str command:
              Command string to execute.
  
          :param str shell:
              Shell to use when executing ``command``.
  
          :param dict env:
              Environment dict used to prep shell environment.
  
          .. versionadded:: 1.0
          """
          raise NotImplementedError
  
      def start_timer(self, timeout):
          """
          Start a timer to `kill` our subprocess after ``timeout`` seconds.
          """
          if timeout is not None:
              self._timer = threading.Timer(timeout, self.kill)
              self._timer.start()
  
      def read_proc_stdout(self, num_bytes):
          """
          Read ``num_bytes`` from the running process' stdout stream.
  
          :param int num_bytes: Number of bytes to read at maximum.
  
          :returns: A string/bytes object.
  
          .. versionadded:: 1.0
          """
          raise NotImplementedError
  
      def read_proc_stderr(self, num_bytes):
          """
          Read ``num_bytes`` from the running process' stderr stream.
  
          :param int num_bytes: Number of bytes to read at maximum.
  
          :returns: A string/bytes object.
  
          .. versionadded:: 1.0
          """
          raise NotImplementedError
  
      def _write_proc_stdin(self, data):
          """
          Write ``data`` to running process' stdin.
  
          This should never be called directly; it's for subclasses to implement.
          See `write_proc_stdin` for the public API call.
  
          :param data: Already-encoded byte data suitable for writing.
  
          :returns: ``None``.
  
          .. versionadded:: 1.0
          """
          raise NotImplementedError
  
      def close_proc_stdin(self):
          """
          Close running process' stdin.
  
          :returns: ``None``.
  
          .. versionadded:: 1.3
          """
          raise NotImplementedError
  
      def default_encoding(self):
          """
          Return a string naming the expected encoding of subprocess streams.
  
          This return value should be suitable for use by encode/decode methods.
  
          .. versionadded:: 1.0
          """
          # TODO: probably wants to be 2 methods, one for local and one for
          # subprocess. For now, good enough to assume both are the same.
          return default_encoding()
  
      def send_interrupt(self, interrupt):
          """
          Submit an interrupt signal to the running subprocess.
  
          In almost all implementations, the default behavior is what will be
          desired: submit ``\x03`` to the subprocess' stdin pipe. However, we
          leave this as a public method in case this default needs to be
          augmented or replaced.
  
          :param interrupt:
              The locally-sourced ``KeyboardInterrupt`` causing the method call.
  
          :returns: ``None``.
  
          .. versionadded:: 1.0
          """
          self.write_proc_stdin(u"\x03")
  
      def returncode(self):
          """
          Return the numeric return/exit code resulting from command execution.
  
          :returns: `int`
  
          .. versionadded:: 1.0
          """
          raise NotImplementedError
  
      def stop(self):
          """
          Perform final cleanup, if necessary.
  
          This method is called within a ``finally`` clause inside the main `run`
          method. Depending on the subclass, it may be a no-op, or it may do
          things such as close network connections or open files.
  
          :returns: ``None``
  
          .. versionadded:: 1.0
          """
          raise NotImplementedError
  
      def stop_timer(self):
          """
          Cancel an open timeout timer, if required.
          """
          # TODO 2.0: merge with stop() (i.e. make stop() something users extend
          # and call super() in, instead of completely overriding, then just move
          # this into the default implementation of stop().
          # TODO: this
          if self._timer:
              self._timer.cancel()
  
      def kill(self):
          """
          Forcibly terminate the subprocess.
  
          Typically only used by the timeout functionality.
  
          This is often a "best-effort" attempt, e.g. remote subprocesses often
          must settle for simply shutting down the local side of the network
          connection and hoping the remote end eventually gets the message.
          """
          raise NotImplementedError
  
      @property
      def timed_out(self):
          """
          Returns ``True`` if the subprocess stopped because it timed out.
  
          .. versionadded:: 1.3
          """
          # Timer expiry implies we did time out. (The timer itself will have
          # killed the subprocess, allowing us to even get to this point.)
          return self._timer and not self._timer.is_alive()
  
  
  class Local(Runner):
      """
      Execute a command on the local system in a subprocess.
  
      .. note::
          When Invoke itself is executed without a controlling terminal (e.g.
          when ``sys.stdin`` lacks a useful ``fileno``), it's not possible to
          present a handle on our PTY to local subprocesses. In such situations,
          `Local` will fallback to behaving as if ``pty=False`` (on the theory
          that degraded execution is better than none at all) as well as printing
          a warning to stderr.
  
          To disable this behavior, say ``fallback=False``.
  
      .. versionadded:: 1.0
      """
  
      def __init__(self, context):
          super(Local, self).__init__(context)
          # Bookkeeping var for pty use case
          self.status = None
  
      def should_use_pty(self, pty=False, fallback=True):
          use_pty = False
          if pty:
              use_pty = True
              # TODO: pass in & test in_stream, not sys.stdin
              if not has_fileno(sys.stdin) and fallback:
                  if not self.warned_about_pty_fallback:
                      err = "WARNING: stdin has no fileno; falling back to non-pty execution!\n"  # noqa
                      sys.stderr.write(err)
                      self.warned_about_pty_fallback = True
                  use_pty = False
          return use_pty
  
      def read_proc_stdout(self, num_bytes):
          # Obtain useful read-some-bytes function
          if self.using_pty:
              # Need to handle spurious OSErrors on some Linux platforms.
              try:
                  data = os.read(self.parent_fd, num_bytes)
              except OSError as e:
                  # Only eat I/O specific OSErrors so we don't hide others
                  stringified = str(e)
                  io_errors = (
                      # The typical default
                      "Input/output error",
                      # Some less common platforms phrase it this way
                      "I/O error",
                  )
                  if not any(error in stringified for error in io_errors):
                      raise
                  # The bad OSErrors happen after all expected output has
                  # appeared, so we return a falsey value, which triggers the
                  # "end of output" logic in code using reader functions.
                  data = None
          else:
              data = os.read(self.process.stdout.fileno(), num_bytes)
          return data
  
      def read_proc_stderr(self, num_bytes):
          # NOTE: when using a pty, this will never be called.
          # TODO: do we ever get those OSErrors on stderr? Feels like we could?
          return os.read(self.process.stderr.fileno(), num_bytes)
  
      def _write_proc_stdin(self, data):
          # NOTE: parent_fd from os.fork() is a read/write pipe attached to our
          # forked process' stdout/stdin, respectively.
          fd = self.parent_fd if self.using_pty else self.process.stdin.fileno()
          # Try to write, ignoring broken pipes if encountered (implies child
          # process exited before the process piping stdin to us finished;
          # there's nothing we can do about that!)
          try:
              return os.write(fd, data)
          except OSError as e:
              if "Broken pipe" not in str(e):
                  raise
  
      def close_proc_stdin(self):
          if self.using_pty:
              # there is no working scenario to tell the process that stdin
              # closed when using pty
              raise SubprocessPipeError("Cannot close stdin when pty=True")
          self.process.stdin.close()
  
      def start(self, command, shell, env):
          if self.using_pty:
              if pty is None:  # Encountered ImportError
                  err = "You indicated pty=True, but your platform doesn't support the 'pty' module!"  # noqa
                  sys.exit(err)
              cols, rows = pty_size()
              self.pid, self.parent_fd = pty.fork()
              # If we're the child process, load up the actual command in a
              # shell, just as subprocess does; this replaces our process - whose
              # pipes are all hooked up to the PTY - with the "real" one.
              if self.pid == 0:
                  # TODO: both pty.spawn() and pexpect.spawn() do a lot of
                  # setup/teardown involving tty.setraw, getrlimit, signal.
                  # Ostensibly we'll want some of that eventually, but if
                  # possible write tests - integration-level if necessary -
                  # before adding it!
                  #
                  # Set pty window size based on what our own controlling
                  # terminal's window size appears to be.
                  # TODO: make subroutine?
                  winsize = struct.pack("HHHH", rows, cols, 0, 0)
                  fcntl.ioctl(sys.stdout.fileno(), termios.TIOCSWINSZ, winsize)
                  # Use execve for bare-minimum "exec w/ variable # args + env"
                  # behavior. No need for the 'p' (use PATH to find executable)
                  # for now.
                  # TODO: see if subprocess is using equivalent of execvp...
                  os.execve(shell, [shell, "-c", command], env)
          else:
              self.process = Popen(
                  command,
                  shell=True,
                  executable=shell,
                  env=env,
                  stdout=PIPE,
                  stderr=PIPE,
                  stdin=PIPE,
              )
  
      def kill(self):
          pid = self.pid if self.using_pty else self.process.pid
          os.kill(pid, signal.SIGKILL)
  
      @property
      def process_is_finished(self):
          if self.using_pty:
              # NOTE:
              # https://github.com/pexpect/ptyprocess/blob/4058faa05e2940662ab6da1330aa0586c6f9cd9c/ptyprocess/ptyprocess.py#L680-L687
              # implies that Linux "requires" use of the blocking, non-WNOHANG
              # version of this call. Our testing doesn't verify this, however,
              # so...
              # NOTE: It does appear to be totally blocking on Windows, so our
              # issue #351 may be totally unsolvable there. Unclear.
              pid_val, self.status = os.waitpid(self.pid, os.WNOHANG)
              return pid_val != 0
          else:
              return self.process.poll() is not None
  
      def returncode(self):
          if self.using_pty:
              # No subprocess.returncode available; use WIFEXITED/WIFSIGNALED to
              # determine whch of WEXITSTATUS / WTERMSIG to use.
              # TODO: is it safe to just say "call all WEXITSTATUS/WTERMSIG and
              # return whichever one of them is nondefault"? Probably not?
              # NOTE: doing this in an arbitrary order should be safe since only
              # one of the WIF* methods ought to ever return True.
              code = None
              if os.WIFEXITED(self.status):
                  code = os.WEXITSTATUS(self.status)
              elif os.WIFSIGNALED(self.status):
                  code = os.WTERMSIG(self.status)
                  # Match subprocess.returncode by turning signals into negative
                  # 'exit code' integers.
                  code = -1 * code
              return code
              # TODO: do we care about WIFSTOPPED? Maybe someday?
          else:
              self.process.wait(timeout=3)
              return self.process.returncode
  
      def stop(self):
          # No explicit close-out required (so far).
          pass
  
  
  class Result(object):
      """
      A container for information about the result of a command execution.
  
      All params are exposed as attributes of the same name and type.
  
      :param str stdout:
          The subprocess' standard output.
  
      :param str stderr:
          Same as ``stdout`` but containing standard error (unless the process
          was invoked via a pty, in which case it will be empty; see
          `.Runner.run`.)
  
      :param str encoding:
          The string encoding used by the local shell environment.
  
      :param str command:
          The command which was executed.
  
      :param str shell:
          The shell binary used for execution.
  
      :param dict env:
          The shell environment used for execution. (Default is the empty dict,
          ``{}``, not ``None`` as displayed in the signature.)
  
      :param int exited:
          An integer representing the subprocess' exit/return code.
  
          .. note::
              This may be ``None`` in situations where the subprocess did not run
              to completion, such as when auto-responding failed or a timeout was
              reached.
  
      :param bool pty:
          A boolean describing whether the subprocess was invoked with a pty or
          not; see `.Runner.run`.
  
      :param tuple hide:
          A tuple of stream names (none, one or both of ``('stdout', 'stderr')``)
          which were hidden from the user when the generating command executed;
          this is a normalized value derived from the ``hide`` parameter of
          `.Runner.run`.
  
          For example, ``run('command', hide='stdout')`` will yield a `Result`
          where ``result.hide == ('stdout',)``; ``hide=True`` or ``hide='both'``
          results in ``result.hide == ('stdout', 'stderr')``; and ``hide=False``
          (the default) generates ``result.hide == ()`` (the empty tuple.)
  
      .. note::
          `Result` objects' truth evaluation is equivalent to their `.ok`
          attribute's value. Therefore, quick-and-dirty expressions like the
          following are possible::
  
              if run("some shell command"):
                  do_something()
              else:
                  handle_problem()
  
          However, remember `Zen of Python #2
          <http://zen-of-python.info/explicit-is-better-than-implicit.html#2>`_.
  
      .. versionadded:: 1.0
      """
  
      # TODO: inherit from namedtuple instead? heh (or: use attrs from pypi)
      def __init__(
          self,
          stdout="",
          stderr="",
          encoding=None,
          command="",
          shell="",
          env=None,
          exited=0,
          pty=False,
          hide=tuple(),
      ):
          self.stdout = stdout
          self.stderr = stderr
          if encoding is None:
              encoding = default_encoding()
          self.encoding = encoding
          self.command = command
          self.shell = shell
          self.env = {} if env is None else env
          self.exited = exited
          self.pty = pty
          self.hide = hide
  
      @property
      def return_code(self):
          """
          An alias for ``.exited``.
  
          .. versionadded:: 1.0
          """
          return self.exited
  
      def __nonzero__(self):
          # NOTE: This is the method that (under Python 2) determines Boolean
          # behavior for objects.
          return self.ok
  
      def __bool__(self):
          # NOTE: And this is the Python 3 equivalent of __nonzero__. Much better
          # name...
          return self.__nonzero__()
  
      def __str__(self):
          if self.exited is not None:
              desc = "Command exited with status {}.".format(self.exited)
          else:
              desc = "Command was not fully executed due to watcher error."
          ret = [desc]
          for x in ("stdout", "stderr"):
              val = getattr(self, x)
              ret.append(
                  u"""=== {} ===
  {}
  """.format(
                      x, val.rstrip()
                  )
                  if val
                  else u"(no {})".format(x)
              )
          return u"\n".join(ret)
  
      def __repr__(self):
          # TODO: more? e.g. len of stdout/err? (how to represent cleanly in a
          # 'x=y' format like this? e.g. '4b' is ambiguous as to what it
          # represents
          template = "<Result cmd={!r} exited={}>"
          return template.format(self.command, self.exited)
  
      @property
      def ok(self):
          """
          A boolean equivalent to ``exited == 0``.
  
          .. versionadded:: 1.0
          """
          return self.exited == 0
  
      @property
      def failed(self):
          """
          The inverse of ``ok``.
  
          I.e., ``True`` if the program exited with a nonzero return code, and
          ``False`` otherwise.
  
          .. versionadded:: 1.0
          """
          return not self.ok
  
      def tail(self, stream, count=10):
          """
          Return the last ``count`` lines of ``stream``, plus leading whitespace.
  
          :param str stream:
              Name of some captured stream attribute, eg ``"stdout"``.
          :param int count:
              Number of lines to preserve.
  
          .. versionadded:: 1.3
          """
          # TODO: preserve alternate line endings? Mehhhh
          # NOTE: no trailing \n preservation; easier for below display if
          # normalized
          text = "\n\n" + "\n".join(getattr(self, stream).splitlines()[-count:])
          return encode_output(text, self.encoding)
  
  
  def normalize_hide(val):
      hide_vals = (None, False, "out", "stdout", "err", "stderr", "both", True)
      if val not in hide_vals:
          err = "'hide' got {!r} which is not in {!r}"
          raise ValueError(err.format(val, hide_vals))
      if val in (None, False):
          hide = ()
      elif val in ("both", True):
          hide = ("stdout", "stderr")
      elif val == "out":
          hide = ("stdout",)
      elif val == "err":
          hide = ("stderr",)
      else:
          hide = (val,)
      return hide
  
  
  def default_encoding():
      """
      Obtain apparent interpreter-local default text encoding.
  
      Often used as a baseline in situations where we must use SOME encoding for
      unknown-but-presumably-text bytes, and the user has not specified an
      override.
      """
      # Based on some experiments there is an issue with
      # `locale.getpreferredencoding(do_setlocale=False)` in Python 2.x on
      # Linux and OS X, and `locale.getpreferredencoding(do_setlocale=True)`
      # triggers some global state changes. (See #274 for discussion.)
      encoding = locale.getpreferredencoding(False)
      if six.PY2 and not WINDOWS:
          default = locale.getdefaultlocale()[1]
          if default is not None:
              encoding = default
      return encoding
  