Add option in ros2 topic pub to wait for N matching subscriptions, use N=1 by default when combined with --times

ros2topic/ros2topic/verb/pub.py

@@ -83,6 +83,11 @@ def add_arguments(self, parser, cli_name):
         group.add_argument(
             '-t', '--times', type=nonnegative_int, default=0,
             help='Publish this number of times and then exit')
+        parser.add_argument(
+            '-w', '--wait-matching-subscriptions', type=nonnegative_int, default=None,
+            help=(
+                'Wait until finding the specified number of matching subscriptions. '
+                'Defaults to 1 when using "-1"/"--once"/"--times", otherwise defaults to 0.'))
         parser.add_argument(
             '--keep-alive', metavar='N', type=positive_float, default=0.1,
             help='Keep publishing node alive for N seconds after the last msg '
@@ -146,6 +151,8 @@ def main(args):
             1. / args.rate,
             args.print,
             times,
+            args.wait_matching_subscriptions
+            if args.wait_matching_subscriptions is not None else int(times != 0),
             qos_profile,
             args.keep_alive)
 
@@ -158,6 +165,7 @@ def publisher(
     period: float,
     print_nth: int,
     times: int,
+    wait_matching_subscriptions: int,
     qos_profile: QoSProfile,
     keep_alive: float,
 ) -> Optional[str]:
@@ -172,6 +180,15 @@ def publisher(
 
     pub = node.create_publisher(msg_module, topic_name, qos_profile)
 
+    times_since_last_log = 0
+    while pub.get_subscription_count() < wait_matching_subscriptions:
+        # Print a message reporting we're waiting each 1s, check condition each 100ms.
+        if not times_since_last_log:
+            print(
+                f'Waiting for at least {wait_matching_subscriptions} matching subscription(s)...')
+        times_since_last_log = (times_since_last_log + 1) % 10
+        time.sleep(0.1)
+
     msg = msg_module()
     try:
         set_message_fields(msg, values_dictionary)
@@ -188,8 +205,6 @@ def timer_callback():
             print('publishing #%d: %r\n' % (count, msg))
         pub.publish(msg)
 
-    # give some time for discovery process
-    time.sleep(0.1)
     timer_callback()
     if times != 1:
         timer = node.create_timer(period, timer_callback)

ros2topic/test/test_cli.py

@@ -660,7 +660,7 @@ def test_topic_pub(self):
                     'publisher: beginning loop',
                     "publishing #1: std_msgs.msg.String(data='foo')",
                     ''
-                ], strict=True
+                ]
             ), timeout=10)
             assert self.listener_node.wait_for_output(functools.partial(
                 launch_testing.tools.expect_output, expected_lines=[
@@ -686,7 +686,7 @@ def test_topic_pub_once(self):
                     'publisher: beginning loop',
                     "publishing #1: std_msgs.msg.String(data='bar')",
                     ''
-                ], strict=True
+                ]
             ), timeout=10)
             assert topic_command.wait_for_shutdown(timeout=10)
             assert self.listener_node.wait_for_output(functools.partial(
@@ -696,6 +696,51 @@ def test_topic_pub_once(self):
             ), timeout=10)
         assert topic_command.exit_code == launch_testing.asserts.EXIT_OK
 
+    def test_topic_pub_once_matching_two_listeners(
+        self, launch_service, proc_info, proc_output, path_to_listener_node_script, additional_env
+    ):
+        second_listener_node_action = Node(
+            executable=sys.executable,
+            arguments=[path_to_listener_node_script],
+            remappings=[('chatter', 'chit_chatter')],
+            additional_env=additional_env,
+            name='second_listener',
+        )
+        with launch_testing.tools.launch_process(
+            launch_service, second_listener_node_action, proc_info, proc_output
+        ) as second_listener_node, \
+            self.launch_topic_command(
+                arguments=[
+                    'pub', '--once',
+                    '--keep-alive', '3',  # seconds
+                    '-w', '2',
+                    '--qos-durability', 'transient_local',
+                    '--qos-reliability', 'reliable',
+                    '/chit_chatter',
+                    'std_msgs/msg/String',
+                    '{data: bar}'
+                ]
+        ) as topic_command:
+            assert topic_command.wait_for_output(functools.partial(
+                launch_testing.tools.expect_output, expected_lines=[
+                    'publisher: beginning loop',
+                    "publishing #1: std_msgs.msg.String(data='bar')",
+                    ''
+                ]
+            ), timeout=10)
+            assert topic_command.wait_for_shutdown(timeout=10)
+            assert self.listener_node.wait_for_output(functools.partial(
+                launch_testing.tools.expect_output, expected_lines=[
+                    re.compile(r'\[INFO\] \[\d+\.\d*\] \[listener\]: I heard: \[bar\]')
+                ]
+            ), timeout=10)
+            assert second_listener_node.wait_for_output(functools.partial(
+                launch_testing.tools.expect_output, expected_lines=[
+                    re.compile(r'\[INFO\] \[\d+\.\d*\] \[second_listener\]: I heard: \[bar\]')
+                ]
+            ), timeout=10)
+        assert topic_command.exit_code == launch_testing.asserts.EXIT_OK
+
     def test_topic_pub_print_every_two(self):
         with self.launch_topic_command(
             arguments=[
@@ -716,7 +761,7 @@ def test_topic_pub_print_every_two(self):
                     '',
                     "publishing #4: std_msgs.msg.String(data='fizz')",
                     ''
-                ], strict=True
+                ]
             ), timeout=10), 'Output does not match: ' + topic_command.output
             assert self.listener_node.wait_for_output(functools.partial(
                 launch_testing.tools.expect_output, expected_lines=[

ros2topic/test/test_echo_pub.py

@@ -180,7 +180,7 @@ def message_callback(msg):
     @launch_testing.markers.retry_on_failure(times=5)
     def test_pub_times(self, launch_service, proc_info, proc_output):
         command_action = ExecuteProcess(
-            cmd=(['ros2', 'topic', 'pub', '-t', '5', '/clitest/topic/pub_times',
+            cmd=(['ros2', 'topic', 'pub', '-t', '5', '-w', '0', '/clitest/topic/pub_times',
                   'std_msgs/String', 'data: hello']),
             additional_env={
                 'PYTHONUNBUFFERED': '1'