Merging upstream version 127.0.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

4 files changed, 674 insertions, 30 deletions

diff --git a/testing/marionette/client/marionette_driver/geckoinstance.py b/testing/marionette/client/marionette_driver/geckoinstance.py
index e613415886..26ad58f360 100644
--- a/testing/marionette/client/marionette_driver/geckoinstance.py
+++ b/testing/marionette/client/marionette_driver/geckoinstance.py
@@ -29,6 +29,10 @@ from six import reraise
 
 from . import errors
 
+if sys.platform.startswith("darwin"):
+    # Marionette's own processhandler is only used on MacOS for now
+    from .processhandler import UNKNOWN_RETURNCODE, ProcessHandler
+
 
 class GeckoInstance(object):
     required_prefs = {
@@ -388,7 +392,7 @@ class GeckoInstance(object):
             }
         )
 
-        return {
+        args = {
             "binary": self.binary,
             "profile": self.profile,
             "cmdargs": ["-no-remote", "-marionette"] + self.app_args,
@@ -397,6 +401,13 @@ class GeckoInstance(object):
             "process_args": process_args,
         }
 
+        if sys.platform.startswith("darwin"):
+            # Bug 1887666: The custom process handler class for Marionette is
+            # only supported on MacOS at the moment.
+            args["process_class"] = ProcessHandler
+
+        return args
+
     def close(self, clean=False):
         """
         Close the managed Gecko process.
@@ -431,6 +442,19 @@ class GeckoInstance(object):
         self.close(clean=clean)
         self.start()
 
+    def update_process(self, pid, timeout=None):
+        """Update the process to track when the application re-launched itself"""
+        if sys.platform.startswith("darwin"):
+            # The new process handler is only supported on MacOS yet
+            returncode = self.runner.process_handler.update_process(pid, timeout)
+            if returncode not in [0, UNKNOWN_RETURNCODE]:
+                raise IOError(
+                    f"Old process inappropriately quit with exit code: {returncode}"
+                )
+
+        else:
+            returncode = self.runner.process_handler.check_for_detached(pid)
+
 
 class FennecInstance(GeckoInstance):
     fennec_prefs = {
@@ -454,7 +478,7 @@ class FennecInstance(GeckoInstance):
         package_name=None,
         env=None,
         *args,
-        **kwargs
+        **kwargs,
     ):
         required_prefs = deepcopy(FennecInstance.fennec_prefs)
         required_prefs.update(kwargs.get("prefs", {}))
diff --git a/testing/marionette/client/marionette_driver/marionette.py b/testing/marionette/client/marionette_driver/marionette.py
index a4b8c73792..7eefde4fc6 100644
--- a/testing/marionette/client/marionette_driver/marionette.py
+++ b/testing/marionette/client/marionette_driver/marionette.py
@@ -568,7 +568,7 @@ class Marionette(object):
         baseurl=None,
         socket_timeout=None,
         startup_timeout=None,
-        **instance_args
+        **instance_args,
     ):
         """Construct a holder for the Marionette connection.
 
@@ -1273,6 +1273,8 @@ class Marionette(object):
                 exc_cls, _, tb = sys.exc_info()
 
                 if self.instance.runner.returncode is None:
+                    self.is_shutting_down = False
+
                     # The process is still running, which means the shutdown
                     # request was not correct or the application ignored it.
                     # Allow Marionette to accept connections again.
@@ -1291,34 +1293,29 @@ class Marionette(object):
                         tb,
                     )
 
-            finally:
-                self.is_shutting_down = False
+            self.is_shutting_down = False
 
+            # Create a new session to retrieve the new process id of the application
             self.delete_session(send_request=False)
 
         else:
             self.delete_session()
             self.instance.restart(clean=clean)
+
             self.raise_for_port(timeout=self.DEFAULT_STARTUP_TIMEOUT)
 
             restart_details.update({"in_app": False, "forced": True})
 
+        self.start_session(self.requested_capabilities, process_forked=in_app)
+        # Restore the context as used before the restart
+        self.set_context(context)
+
         if restart_details.get("cause") not in (None, "restart"):
             raise errors.MarionetteException(
                 "Unexpected shutdown reason '{}' for "
                 "restarting the process".format(restart_details["cause"])
             )
 
-        self.start_session(self.requested_capabilities)
-        # Restore the context as used before the restart
-        self.set_context(context)
-
-        if in_app and self.process_id:
-            # In some cases Firefox restarts itself by spawning into a new process group.
-            # As long as mozprocess cannot track that behavior (bug 1284864) we assist by
-            # informing about the new process id.
-            self.instance.runner.process_handler.check_for_detached(self.process_id)
-
         return restart_details
 
     def absolute_url(self, relative_url):
@@ -1330,7 +1327,7 @@ class Marionette(object):
         return "{0}{1}".format(self.baseurl, relative_url)
 
     @do_process_check
-    def start_session(self, capabilities=None, timeout=None):
+    def start_session(self, capabilities=None, process_forked=False, timeout=None):
         """Create a new WebDriver session.
         This method must be called before performing any other action.
 
@@ -1340,7 +1337,10 @@ class Marionette(object):
             (including alwaysMatch, firstMatch, desiredCapabilities,
             or requriedCapabilities), and only recognises extension
             capabilities that are specific to Marionette.
+        :param process_forked: If True, the existing process forked itself due
+        to an internal restart.
         :param timeout: Optional timeout in seconds for the server to be ready.
+
         :returns: A dictionary of the capabilities offered.
         """
         if capabilities is None:
@@ -1352,17 +1352,20 @@ class Marionette(object):
 
         self.crashed = 0
 
-        if self.instance:
-            returncode = self.instance.runner.returncode
-            # We're managing a binary which has terminated. Start it again
-            # and implicitely wait for the Marionette server to be ready.
-            if returncode is not None:
-                self.start_binary(timeout)
+        if not process_forked:
+            # Only handle the binary if there was no process before which also
+            # might have forked itself due to a restart
+            if self.instance:
+                returncode = self.instance.runner.returncode
+                # We're managing a binary which has terminated. Start it again
+                # and implicitely wait for the Marionette server to be ready.
+                if returncode is not None:
+                    self.start_binary(timeout)
 
-        else:
-            # In the case when Marionette doesn't manage the binary wait until
-            # its server component has been started.
-            self.raise_for_port(timeout=timeout)
+            else:
+                # In the case when Marionette doesn't manage the binary wait until
+                # its server component has been started.
+                self.raise_for_port(timeout=timeout)
 
         self.client = transport.TcpTransport(self.host, self.port, self.socket_timeout)
         self.protocol, _ = self.client.connect()
@@ -1380,10 +1383,11 @@ class Marionette(object):
         self.session_id = resp["sessionId"]
         self.session = resp["capabilities"]
         self.cleanup_ran = False
-        # fallback to processId can be removed in Firefox 55
-        self.process_id = self.session.get(
-            "moz:processID", self.session.get("processId")
-        )
+
+        self.process_id = self.session.get("moz:processID")
+        if process_forked:
+            self.instance.update_process(self.process_id, self.shutdown_timeout)
+
         self.profile = self.session.get("moz:profile")
 
         timeout = self.session.get("moz:shutdownTimeout")
diff --git a/testing/marionette/client/marionette_driver/processhandler.py b/testing/marionette/client/marionette_driver/processhandler.py
new file mode 100644
index 0000000000..deac1b02ea
--- /dev/null
+++ b/testing/marionette/client/marionette_driver/processhandler.py
@@ -0,0 +1,615 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this file,
+# You can obtain one at http://mozilla.org/MPL/2.0/.
+
+# The Marionette ProcessHandler and ProcessHandlerMixin classes are only
+# utilized by Marionette as an alternative to the mozprocess package.
+#
+# This necessity arises because Marionette supports the application to
+# restart itself and, under such conditions, fork its process. To maintain
+# the ability to track the process, including permissions to terminate
+# the process and receive log entries via stdout and stderr, the psutil
+# package is utilized. To prevent any side effects for consumers of
+# mozprocess, all necessary helper classes have been duplicated for now.
+
+import codecs
+import os
+import signal
+import subprocess
+import sys
+import threading
+import time
+import traceback
+from queue import Empty, Queue
+
+import psutil
+import six
+
+# Set the MOZPROCESS_DEBUG environment variable to 1 to see some debugging output
+MOZPROCESS_DEBUG = os.getenv("MOZPROCESS_DEBUG")
+
+INTERVAL_PROCESS_ALIVE_CHECK = 0.02
+
+# For not self-managed processes the returncode seems to not be available.
+# Use `8` to indicate this specific situation for now.
+UNKNOWN_RETURNCODE = 8
+
+# We dont use mozinfo because it is expensive to import, see bug 933558.
+isPosix = os.name == "posix"  # includes MacOS X
+
+
+class ProcessHandlerMixin(object):
+    """
+    A class for launching and manipulating local processes.
+
+    :param cmd: command to run. May be a string or a list. If specified as a list, the first
+      element will be interpreted as the command, and all additional elements will be interpreted
+      as arguments to that command.
+    :param args: list of arguments to pass to the command (defaults to None). Must not be set when
+      `cmd` is specified as a list.
+    :param cwd: working directory for command (defaults to None).
+    :param env: is the environment to use for the process (defaults to os.environ).
+    :param kill_on_timeout: when True, the process will be killed when a timeout is reached.
+      When False, the caller is responsible for killing the process.
+      Failure to do so could cause a call to wait() to hang indefinitely. (Defaults to True.)
+    :param processOutputLine: function or list of functions to be called for
+        each line of output produced by the process (defaults to an empty
+        list).
+    :param processStderrLine: function or list of functions to be called
+        for each line of error output - stderr - produced by the process
+        (defaults to an empty list). If this is not specified, stderr lines
+        will be sent to the *processOutputLine* callbacks.
+    :param onTimeout: function or list of functions to be called when the process times out.
+    :param onFinish: function or list of functions to be called when the process terminates
+      normally without timing out.
+    :param kwargs: additional keyword args to pass directly into Popen.
+
+    NOTE: Child processes will be tracked by default.
+    """
+
+    def __init__(
+        self,
+        cmd,
+        args=None,
+        cwd=None,
+        env=None,
+        kill_on_timeout=True,
+        processOutputLine=(),
+        processStderrLine=(),
+        onTimeout=(),
+        onFinish=(),
+        **kwargs,
+    ):
+        self.args = args
+        self.cmd = cmd
+        self.cwd = cwd
+        self.keywordargs = kwargs
+
+        self.didTimeout = False
+        self.didOutputTimeout = False
+        self.proc = None
+
+        if env is None:
+            env = os.environ.copy()
+        self.env = env
+
+        # handlers
+        def to_callable_list(arg):
+            if callable(arg):
+                arg = [arg]
+            return CallableList(arg)
+
+        processOutputLine = to_callable_list(processOutputLine)
+        processStderrLine = to_callable_list(processStderrLine)
+        onTimeout = to_callable_list(onTimeout)
+        onFinish = to_callable_list(onFinish)
+
+        def on_timeout():
+            self.didTimeout = True
+            self.didOutputTimeout = self.reader.didOutputTimeout
+            if kill_on_timeout:
+                self.kill()
+
+        onTimeout.insert(0, on_timeout)
+
+        self._stderr = subprocess.STDOUT
+        if processStderrLine:
+            self._stderr = subprocess.PIPE
+        self.reader = ProcessReader(
+            stdout_callback=processOutputLine,
+            stderr_callback=processStderrLine,
+            finished_callback=onFinish,
+            timeout_callback=onTimeout,
+        )
+
+        # It is common for people to pass in the entire array with the cmd and
+        # the args together since this is how Popen uses it.  Allow for that.
+        if isinstance(self.cmd, list):
+            if self.args is not None:
+                raise TypeError("cmd and args must not both be lists")
+            (self.cmd, self.args) = (self.cmd[0], self.cmd[1:])
+        elif self.args is None:
+            self.args = []
+
+    def _has_valid_proc(func):
+        def wrapper(self, *args, **kwargs):
+            if self.proc is None:
+                raise RuntimeError("Process hasn't been started yet")
+            return func(self, *args, **kwargs)
+
+        return wrapper
+
+    @property
+    @_has_valid_proc
+    def pid(self):
+        return self.proc.pid
+
+    @staticmethod
+    def pid_exists(pid):
+        return psutil.pid_exists(pid)
+
+    @property
+    def timedOut(self):
+        """True if the process has timed out for any reason."""
+        return self.didTimeout
+
+    @property
+    def outputTimedOut(self):
+        """True if the process has timed out for no output."""
+        return self.didOutputTimeout
+
+    @property
+    def commandline(self):
+        """the string value of the command line (command + args)"""
+        return subprocess.list2cmdline([self.cmd] + self.args)
+
+    def _debug(self, msg):
+        if not MOZPROCESS_DEBUG:
+            return
+
+        print(f"DBG::MARIONETTE ProcessHandler {self.pid} | {msg}", file=sys.stdout)
+
+    @_has_valid_proc
+    def kill(self, sig=None, timeout=None):
+        """Kills the managed process and all its child processes.
+
+        :param sig: Signal to use to kill the process. (Defaults to SIGKILL)
+
+        :param timeout: If not None, wait this number of seconds for the
+        process to exit.
+
+        Note that this does not manage any state, save any output etc,
+        it immediately kills the process.
+        """
+        if hasattr(self, "returncode"):
+            return self.returncode
+
+        if self.proc.is_running():
+            processes = [self.proc] + self.proc.children(recursive=True)
+
+            if sig is None:
+                # TODO: try SIGTERM first to sanely shutdown the application
+                # and to not break later when Windows support gets added.
+                sig = signal.SIGKILL
+
+            # Do we need that?
+            for process in processes:
+                try:
+                    self._debug(f"Killing process: {process}")
+                    process.send_signal(sig)
+                except psutil.NoSuchProcess:
+                    pass
+            psutil.wait_procs(processes, timeout=timeout)
+
+        # When we kill the the managed process we also have to wait for the
+        # reader thread to be finished. Otherwise consumers would have to assume
+        # that it still has not completely shutdown.
+        self.returncode = self.wait(0)
+        if self.returncode is None:
+            self._debug("kill: wait failed -- process is still alive")
+
+        return self.returncode
+
+    @_has_valid_proc
+    def poll(self):
+        """Check if child process has terminated
+
+        Returns the current returncode value:
+        - None if the process hasn't terminated yet
+        - A negative number if the process was killed by signal N (Unix only)
+        - '0' if the process ended without failures
+
+        """
+        if hasattr(self, "returncode"):
+            return self.returncode
+
+        # If the process that is observed wasn't started with Popen there is
+        # no `poll()` method available. Use `wait()` instead and do not wait
+        # for the reader thread because it would cause extra delays.
+        return self.wait(0, wait_reader=False)
+
+    def processOutput(self, timeout=None, outputTimeout=None):
+        """
+        Handle process output until the process terminates or times out.
+
+        :param timeout: If not None, the process will be allowed to continue
+        for that number of seconds before being killed.
+
+        :outputTimeout: If not None, the process will be allowed to continue
+        for that number of seconds without producing any output before
+        being killed.
+        """
+        # this method is kept for backward compatibility
+        if not hasattr(self, "proc"):
+            self.run(timeout=timeout, outputTimeout=outputTimeout)
+            # self.run will call this again
+            return
+        if not self.reader.is_alive():
+            self.reader.timeout = timeout
+            self.reader.output_timeout = outputTimeout
+            self.reader.start(self.proc)
+
+    def run(self, timeout=None, outputTimeout=None):
+        """
+        Starts the process.
+
+        :param timeout: If not None, the process will be allowed to continue for
+        that number of seconds before being killed. If the process is killed
+        due to a timeout, the onTimeout handler will be called.
+
+        :outputTimeout: If not None, the process will be allowed to continue
+        for that number of seconds without producing any output before
+        being killed.
+        """
+        self.didTimeout = False
+        self.didOutputTimeout = False
+
+        # default arguments
+        args = dict(
+            stdout=subprocess.PIPE,
+            stderr=self._stderr,
+            cwd=self.cwd,
+            env=self.env,
+        )
+
+        # build process arguments
+        args.update(self.keywordargs)
+
+        # launch the process
+        self.proc = psutil.Popen([self.cmd] + self.args, **args)
+
+        self.processOutput(timeout=timeout, outputTimeout=outputTimeout)
+
+    @_has_valid_proc
+    def update_process(self, new_pid, timeout=None):
+        """Update the internally managed process for the provided process ID.
+
+        When the application restarts itself, such as during an update, the new
+        process is essentially a fork of itself. To continue monitoring this
+        process, the process ID needs to be updated accordingly.
+
+        :param new_pid: The ID of the new (forked) process to track.
+
+        :timeout: If not None, the old process will be allowed to continue for
+        that number of seconds before being killed.
+        """
+        if isPosix:
+            if new_pid == self.pid:
+                return
+
+            print(
+                'Child process with id "%s" has been marked as detached because it is no '
+                "longer in the managed process group. Keeping reference to the process id "
+                '"%s" which is the new child process.' % (self.pid, new_pid),
+                file=sys.stdout,
+            )
+
+            returncode = self.wait(timeout, wait_reader=False)
+            if returncode is None:
+                # If the process is still running force kill it.
+                returncode = self.kill()
+
+            if hasattr(self, "returncode"):
+                del self.returncode
+
+            self.proc = psutil.Process(new_pid)
+            self._debug(
+                f"New process status: {self.proc} (terminal={self.proc.terminal()})"
+            )
+
+            return returncode
+
+    @_has_valid_proc
+    def wait(self, timeout=None, wait_reader=True):
+        """
+        Waits until the process is terminated.
+
+        :param timeout: If not None, will return after timeout seconds.
+        This timeout only causes the wait function to return and
+        does not kill the process.
+
+        :param wait_reader: If set to True, it waits not only for the process
+        to exit but also for all output to be fully read. (Defaults to True).
+
+        Returns the process exit code value:
+        - None if the process hasn't terminated yet
+        - A negative number if the process was killed by signal N (Unix only)
+        - '0' if the process ended without failures
+
+        """
+        # Thread.join() blocks the main thread until the reader thread is finished
+        # wake up once a second in case a keyboard interrupt is sent
+        if (
+            wait_reader
+            and self.reader.thread
+            and self.reader.thread is not threading.current_thread()
+        ):
+            count = 0
+            while self.reader.is_alive():
+                if timeout is not None and count > timeout:
+                    self._debug("wait timeout for reader thread")
+                    return None
+                self.reader.join(timeout=1)
+                count += 1
+
+        try:
+            self.proc.wait(timeout)
+            self._debug(f"Process status after wait: {self.proc}")
+
+            if not isinstance(self.proc, psutil.Popen):
+                self._debug(
+                    "Not self-managed processes do not have a returncode. "
+                    f"Setting its value to {UNKNOWN_RETURNCODE}."
+                )
+                self.returncode = UNKNOWN_RETURNCODE
+
+            else:
+                self.returncode = self.proc.returncode
+
+            return self.returncode
+        except psutil.TimeoutExpired:
+            return None
+
+
+class CallableList(list):
+    def __call__(self, *args, **kwargs):
+        for e in self:
+            e(*args, **kwargs)
+
+    def __add__(self, lst):
+        return CallableList(list.__add__(self, lst))
+
+
+class ProcessReader(object):
+    def __init__(
+        self,
+        stdout_callback=None,
+        stderr_callback=None,
+        finished_callback=None,
+        timeout_callback=None,
+        timeout=None,
+        output_timeout=None,
+    ):
+        self.stdout_callback = stdout_callback or (lambda line: True)
+        self.stderr_callback = stderr_callback or (lambda line: True)
+        self.finished_callback = finished_callback or (lambda: True)
+        self.timeout_callback = timeout_callback or (lambda: True)
+        self.timeout = timeout
+        self.output_timeout = output_timeout
+        self.thread = None
+        self.didOutputTimeout = False
+
+    def debug(self, msg):
+        if not MOZPROCESS_DEBUG:
+            return
+
+        print("DBG::MARIONETTE ProcessReader | {}".format(msg), file=sys.stdout)
+
+    def _create_stream_reader(self, name, stream, queue, callback):
+        thread = threading.Thread(
+            name=name, target=self._read_stream, args=(stream, queue, callback)
+        )
+        thread.daemon = True
+        thread.start()
+        return thread
+
+    def _read_stream(self, stream, queue, callback):
+        while True:
+            line = stream.readline()
+            if not line:
+                break
+            queue.put((line, callback))
+        stream.close()
+
+    def start(self, proc):
+        queue = Queue()
+        stdout_reader = None
+        if proc.stdout:
+            stdout_reader = self._create_stream_reader(
+                "ProcessReaderStdout", proc.stdout, queue, self.stdout_callback
+            )
+        stderr_reader = None
+        if proc.stderr and proc.stderr != proc.stdout:
+            stderr_reader = self._create_stream_reader(
+                "ProcessReaderStderr", proc.stderr, queue, self.stderr_callback
+            )
+        self.thread = threading.Thread(
+            name="ProcessReader",
+            target=self._read,
+            args=(stdout_reader, stderr_reader, queue),
+        )
+        self.thread.daemon = True
+        self.thread.start()
+        self.debug("ProcessReader started")
+
+    def _read(self, stdout_reader, stderr_reader, queue):
+        start_time = time.time()
+        timed_out = False
+        timeout = self.timeout
+        if timeout is not None:
+            timeout += start_time
+        output_timeout = self.output_timeout
+        if output_timeout is not None:
+            output_timeout += start_time
+
+        while (stdout_reader and stdout_reader.is_alive()) or (
+            stderr_reader and stderr_reader.is_alive()
+        ):
+            has_line = True
+            try:
+                line, callback = queue.get(True, INTERVAL_PROCESS_ALIVE_CHECK)
+            except Empty:
+                has_line = False
+            now = time.time()
+            if not has_line:
+                if output_timeout is not None and now > output_timeout:
+                    timed_out = True
+                    self.didOutputTimeout = True
+                    break
+            else:
+                if output_timeout is not None:
+                    output_timeout = now + self.output_timeout
+                callback(line.rstrip())
+            if timeout is not None and now > timeout:
+                timed_out = True
+                break
+        self.debug("_read loop exited")
+        # process remaining lines to read
+        while not queue.empty():
+            line, callback = queue.get(False)
+            try:
+                callback(line.rstrip())
+            except Exception:
+                traceback.print_exc()
+        if timed_out:
+            try:
+                self.timeout_callback()
+            except Exception:
+                traceback.print_exc()
+        if stdout_reader:
+            stdout_reader.join()
+        if stderr_reader:
+            stderr_reader.join()
+        if not timed_out:
+            try:
+                self.finished_callback()
+            except Exception:
+                traceback.print_exc()
+        self.debug("_read exited")
+
+    def is_alive(self):
+        if self.thread:
+            return self.thread.is_alive()
+        return False
+
+    def join(self, timeout=None):
+        if self.thread:
+            self.thread.join(timeout=timeout)
+
+
+# default output handlers
+# these should be callables that take the output line
+
+
+class StoreOutput(object):
+    """accumulate stdout"""
+
+    def __init__(self):
+        self.output = []
+
+    def __call__(self, line):
+        self.output.append(line)
+
+
+class StreamOutput(object):
+    """pass output to a stream and flush"""
+
+    def __init__(self, stream, text=True):
+        self.stream = stream
+        self.text = text
+
+    def __call__(self, line):
+        ensure = six.ensure_text if self.text else six.ensure_binary
+        try:
+            self.stream.write(ensure(line, errors="ignore") + ensure("\n"))
+        except TypeError:
+            print(
+                "HEY! If you're reading this, you're about to encounter a "
+                "type error, probably as a result of a conversion from "
+                "Python 2 to Python 3. This is almost definitely because "
+                "you're trying to write binary data to a text-encoded "
+                "stream, or text data to a binary-encoded stream. Check how "
+                "you're instantiating your ProcessHandler and if the output "
+                "should be text-encoded, make sure you pass "
+                "universal_newlines=True.",
+                file=sys.stderr,
+            )
+            raise
+        self.stream.flush()
+
+
+class LogOutput(StreamOutput):
+    """pass output to a file"""
+
+    def __init__(self, filename):
+        self.file_obj = open(filename, "a")
+        StreamOutput.__init__(self, self.file_obj, True)
+
+    def __del__(self):
+        if self.file_obj is not None:
+            self.file_obj.close()
+
+
+# front end class with the default handlers
+
+
+class ProcessHandler(ProcessHandlerMixin):
+    """
+    Convenience class for handling processes with default output handlers.
+
+    By default, all output is sent to stdout. This can be disabled by setting
+    the *stream* argument to None.
+
+    If processOutputLine keyword argument is specified the function or the
+    list of functions specified by this argument will be called for each line
+    of output; the output will not be written to stdout automatically then
+    if stream is True (the default).
+
+    If storeOutput==True, the output produced by the process will be saved
+    as self.output.
+
+    If logfile is not None, the output produced by the process will be
+    appended to the given file.
+    """
+
+    def __init__(self, cmd, logfile=None, stream=True, storeOutput=True, **kwargs):
+        kwargs.setdefault("processOutputLine", [])
+        if callable(kwargs["processOutputLine"]):
+            kwargs["processOutputLine"] = [kwargs["processOutputLine"]]
+
+        if logfile:
+            logoutput = LogOutput(logfile)
+            kwargs["processOutputLine"].append(logoutput)
+
+        text = kwargs.get("universal_newlines", False) or kwargs.get("text", False)
+
+        if stream is True:
+            if text:
+                # The encoding of stdout isn't guaranteed to be utf-8. Fix that.
+                stdout = codecs.getwriter("utf-8")(sys.stdout.buffer)
+            else:
+                stdout = sys.stdout.buffer
+
+            if not kwargs["processOutputLine"]:
+                kwargs["processOutputLine"].append(StreamOutput(stdout, text))
+        elif stream:
+            streamoutput = StreamOutput(stream, text)
+            kwargs["processOutputLine"].append(streamoutput)
+
+        self.output = None
+        if storeOutput:
+            storeoutput = StoreOutput()
+            self.output = storeoutput.output
+            kwargs["processOutputLine"].append(storeoutput)
+
+        ProcessHandlerMixin.__init__(self, cmd, **kwargs)
diff --git a/testing/marionette/client/requirements.txt b/testing/marionette/client/requirements.txt
index 220531c4f5..9e80295034 100644
--- a/testing/marionette/client/requirements.txt
+++ b/testing/marionette/client/requirements.txt
@@ -1,3 +1,4 @@
 mozrunner >= 7.4.0
 mozversion >= 2.1.0
+psutil==5.9.8; sys_platform == 'darwin'  # Bug 1887666: MacOS only for now
 six