Add onchange configuration for script engine

changelog/62867.added

@@ -0,0 +1 @@
+Added onchange configuration for script engine

salt/engines/script.py

@@ -10,13 +10,23 @@ Example Config
           cmd: /some/script.py -a 1 -b 2
           output: json
           interval: 5
+          onchange: false
 
 Script engine configs:
 
-    cmd: Script or command to execute
-    output: Any available saltstack deserializer
-    interval: How often in seconds to execute the command
+cmd
+    Script or command to execute
 
+output
+    Any available saltstack deserializer
+
+interval
+    How often in seconds to execute the command
+
+onchange
+    .. versionadded:: 3006
+
+    Only fire an event if the tag-specific output changes. Defaults to False.
 """
 
 import logging
@@ -53,7 +63,7 @@ def _get_serializer(output):
         )
 
 
-def start(cmd, output="json", interval=1):
+def start(cmd, output="json", interval=1, onchange=False):
     """
     Parse stdout of a command and generate an event
 
@@ -80,6 +90,7 @@ def start(cmd, output="json", interval=1):
     :param cmd: The command to execute
     :param output: How to deserialize stdout of the script
     :param interval: How often to execute the script
+    :param onchange: Only fire an event if the tag-specific output changes
     """
     try:
         cmd = shlex.split(cmd)
@@ -96,7 +107,10 @@ def start(cmd, output="json", interval=1):
     else:
         fire_master = __salt__["event.send"]
 
-    while True:
+    if onchange:
+        events = {}
+
+    while _running():
 
         try:
             proc = subprocess.Popen(
@@ -116,8 +130,12 @@ def start(cmd, output="json", interval=1):
                     data["id"] = __opts__["id"]
 
                 if tag:
+                    if onchange and tag in events and events[tag] == data:
+                        continue
                     log.info("script engine firing event with tag %s", tag)
                     fire_master(tag=tag, data=data)
+                    if onchange:
+                        events[tag] = data
 
             log.debug("Closing script with pid %d", proc.pid)
             proc.stdout.close()
@@ -132,3 +150,8 @@ def start(cmd, output="json", interval=1):
                 proc.terminate()
 
         time.sleep(interval)
+
+
+# helper to test the start function
+def _running():
+    return True

tests/pytests/unit/engines/test_script.py

@@ -2,17 +2,20 @@
 unit tests for the script engine
 """
 
+import copy
+
 import pytest
 
 import salt.config
 import salt.engines.script as script
 from salt.exceptions import CommandExecutionError
-from tests.support.mock import patch
+from tests.support.mock import Mock, patch
 
 
 @pytest.fixture
 def configure_loader_modules():
-    opts = salt.config.DEFAULT_MASTER_OPTS
+    opts = copy.deepcopy(salt.config.DEFAULT_MASTER_OPTS)
+    opts["id"] = "test"
     return {script: {"__opts__": opts}}
 
 
@@ -45,3 +48,85 @@ def test__read_stdout_terminates_properly():
         popen_mock.stdout.readline.return_value = b""
         with pytest.raises(StopIteration):
             next(script._read_stdout(popen_mock))
+
+
+@pytest.fixture()
+def serializer():
+    with patch("salt.engines.script._get_serializer", autospec=True) as get_serializer:
+        serializer = Mock()
+        get_serializer.return_value = serializer
+        serializer.deserialize.side_effect = lambda x: x
+        yield serializer
+
+
+@pytest.fixture(params=[1])
+def runs(request):
+    runs = Mock()
+    runs.side_effect = request.param * [True] + [False]
+    with patch("salt.engines.script._running", runs):
+        yield
+
+
+@pytest.fixture()
+def event_send():
+    event = Mock()
+    with patch("salt.utils.event.get_master_event") as get_master:
+        get_master.fire_event = event
+        with patch.dict(script.__salt__, {"event.send": event}):
+            yield event
+
+
+@pytest.fixture()
+def raw_event():
+    with patch("salt.engines.script._read_stdout") as stdout:
+        yield stdout
+
+
+@pytest.fixture()
+def proc():
+    with patch("salt.engines.script.subprocess.Popen") as popen:
+        proc = Mock()
+        proc.wait.return_value = False
+        proc.pid = 1337
+        popen.return_value = proc
+        yield
+
+
+@pytest.fixture()
+def sleep():
+    with patch("time.sleep"):
+        yield
+
+
+@pytest.fixture()
+def event():
+    return {"tag": "test", "data": {"foo": "bar", "id": "test"}}
+
+
+@pytest.fixture()
+def new_event():
+    return {"tag": "test", "data": {"foo": "baz", "id": "test"}}
+
+
+@pytest.mark.usefixtures(
+    "proc", "serializer", "runs", "sleep", "event_send", "raw_event"
+)
+class TestStart:
+    def test_start(self, event, raw_event, event_send):
+        raw_event.return_value = [event]
+        script.start("cmd")
+        event_send.assert_called_once_with(tag=event["tag"], data=event["data"])
+
+    @pytest.mark.parametrize("runs", [10], indirect=True)
+    def test_start_onchange_no_change(self, event, raw_event, event_send):
+        raw_event.side_effect = 10 * [[event]]
+        script.start("cmd", onchange=True)
+        event_send.assert_called_once_with(tag=event["tag"], data=event["data"])
+
+    @pytest.mark.parametrize("runs", [8], indirect=True)
+    def test_start_onchange_with_change(self, event, new_event, raw_event, event_send):
+        raw_event.side_effect = 3 * [[event]] + 5 * [[new_event]]
+        script.start("cmd", onchange=True)
+        assert event_send.call_count == 2
+        event_send.assert_any_call(tag=event["tag"], data=event["data"])
+        event_send.assert_called_with(tag=new_event["tag"], data=new_event["data"])