Merge branch '93-fail-gracefully-when-lttng-is-not-installed' into 'master'

Fail gracefully when trying to trace if LTTng is not installed

Closes #93

See merge request micro-ROS/ros_tracing/ros2_tracing!174

.gitlab-ci.yml

@@ -50,7 +50,9 @@ no_lttng:
   image: $BASE_IMAGE_ID:$DISTRO-base
   script:
     - colcon build --symlink-install --event-handlers console_cohesion+ --packages-up-to $PACKAGES_LIST
+    - . install/setup.sh
     - (! ./build/tracetools/status)
+    - (! ros2 trace)
     - colcon test --event-handlers console_cohesion+ --packages-select $PACKAGES_LIST
     - colcon test-result --all
   <<: *global_artifacts

tracetools_trace/tracetools_trace/tools/lttng.py

@@ -14,8 +14,9 @@
 
 """Interface for tracing with LTTng."""
 
+import platform
+import subprocess
 import sys
-
 from typing import List
 from typing import Optional
 
@@ -83,3 +84,35 @@ def lttng_fini(
     """
     _lttng.stop(session_name)
     _lttng.destroy(session_name)
+
+
+def is_lttng_installed() -> bool:
+    """
+    Check if LTTng is installed.
+
+    It first checks if the OS can support LTTng.
+    If so, it then simply checks if LTTng is installed using the 'lttng' command.
+
+    :return: True if it is installed, False otherwise
+    """
+    message_doc = (
+        'Cannot trace. See documentation at: '
+        'https://gitlab.com/micro-ROS/ros_tracing/ros2_tracing'
+    )
+    system = platform.system()
+    if 'Linux' != system:
+        print(f"System '{system}' does not support LTTng.\n{message_doc}", file=sys.stderr)
+        return False
+    try:
+        process = subprocess.Popen(
+            ['lttng', '--version'],
+            stdout=subprocess.PIPE,
+            stderr=subprocess.PIPE,
+        )
+        _, stderr = process.communicate()
+        if 0 != process.returncode:
+            raise RuntimeError(stderr.decode())
+        return True
+    except Exception as e:
+        print(f'LTTng not found: {e}\n{message_doc}', file=sys.stderr)
+        return False

tracetools_trace/tracetools_trace/trace.py

@@ -15,6 +15,7 @@
 
 """Entrypoint/script to setup and start an LTTng tracing session."""
 
+import sys
 from typing import List
 
 from tracetools_trace.tools import args
@@ -41,6 +42,9 @@ def init(
     :param context_names: list of context names to enable
     :param display_list: whether to display list(s) of enabled events and context names
     """
+    if not lttng.is_lttng_installed():
+        sys.exit(2)
+
     ust_enabled = len(ros_events) > 0
     kernel_enabled = len(kernel_events) > 0
     if ust_enabled: