Island: Add utils.get_or_create_target_machine()

Both ScanEventHandler and update_nodes_on_exploitation() will need this
functionality. Extracting it some place common.

I didn't put it into the MachineRepository because the semantics of
creating a machine if not found are likely specific to a small set of
use cases, rather than part of the general interface.

monkey/monkey_island/cc/agent_event_handlers/__init__.py

@@ -1,3 +1,4 @@
 from .save_event_to_event_repository import save_event_to_event_repository
 from .save_stolen_credentials_to_repository import save_stolen_credentials_to_repository
 from .scan_event_handler import ScanEventHandler
+from .update_nodes_on_exploitation import update_nodes_on_exploitation

monkey/monkey_island/cc/agent_event_handlers/utils.py

@@ -0,0 +1,17 @@
+from ipaddress import IPv4Address, IPv4Interface
+
+from monkey_island.cc.models import Machine
+from monkey_island.cc.repository import IMachineRepository, UnknownRecordError
+
+
+def get_or_create_target_machine(repository: IMachineRepository, target: IPv4Address):
+    try:
+        target_machines = repository.get_machines_by_ip(target)
+        return target_machines[0]
+    except UnknownRecordError:
+        machine = Machine(
+            id=repository.get_new_id(),
+            network_interfaces=[IPv4Interface(target)],
+        )
+        repository.upsert_machine(machine)
+        return machine

monkey/tests/unit_tests/monkey_island/cc/agent_event_handlers/test_utils.py

@@ -0,0 +1,46 @@
+from ipaddress import IPv4Address, IPv4Interface
+from unittest.mock import MagicMock
+
+import pytest
+
+from monkey_island.cc.agent_event_handlers.utils import get_or_create_target_machine
+from monkey_island.cc.models import Machine
+from monkey_island.cc.repository import IMachineRepository, UnknownRecordError
+
+SEED_ID = 99
+IP_ADDRESS = IPv4Address("10.10.10.99")
+
+EXISTING_MACHINE = Machine(
+    id=1,
+    hardware_id=5,
+    network_interfaces=[IPv4Interface(IP_ADDRESS)],
+)
+
+EXPECTED_CREATED_MACHINE = Machine(
+    id=SEED_ID,
+    network_interfaces=[IPv4Interface(IP_ADDRESS)],
+)
+
+
+@pytest.fixture
+def machine_repository() -> IMachineRepository:
+    machine_repository = MagicMock(spec=IMachineRepository)
+    machine_repository.get_new_id = MagicMock(return_value=SEED_ID)
+    return machine_repository
+
+
+def test_return_existing_machine(machine_repository):
+    machine_repository.get_machines_by_ip = MagicMock(return_value=[EXISTING_MACHINE])
+
+    target_machine = get_or_create_target_machine(machine_repository, IP_ADDRESS)
+
+    assert target_machine == EXISTING_MACHINE
+
+
+def test_create_new_machine(machine_repository):
+    machine_repository.get_machines_by_ip = MagicMock(side_effect=UnknownRecordError)
+
+    target_machine = get_or_create_target_machine(machine_repository, IP_ADDRESS)
+
+    assert target_machine == EXPECTED_CREATED_MACHINE
+    assert machine_repository.upsert_machine.called_once_with(target_machine)