Extract LdPreload action from Trace action to support preloading any lib

tracetools_launch/tracetools_launch/actions/ld_preload.py

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+# Copyright 2019 Apex.AI, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Module for the LdPreload action."""
+
+import subprocess
+from typing import List
+from typing import Optional
+from typing import Union
+
+from launch.action import Action
+from launch.actions import SetEnvironmentVariable
+from launch.launch_context import LaunchContext
+from tracetools_trace.tools import tracing_supported
+
+
+class LdPreload(Action):
+    """Action that adds a SetEnvironmentVariable action to preload a library."""
+
+    ENV_VAR_LD_PRELOAD = 'LD_PRELOAD'
+
+    def __init__(
+        self,
+        lib_name: str,
+        **kwargs,
+    ) -> None:
+        """
+        Create an LdPreload action.
+
+        :param lib_name: the name of the library
+        """
+        super().__init__(**kwargs)
+        self.__lib_name = lib_name
+        self.__set_env_action = None
+        # Try to find lib
+        self.__lib_path = self.get_shared_lib_path(self.__lib_name)
+        # And create action if found
+        if self.__lib_path is not None:
+            self.__set_env_action = SetEnvironmentVariable(
+                self.ENV_VAR_LD_PRELOAD,
+                self.__lib_path,
+            )
+
+    def lib_found(self) -> bool:
+        return self.__set_env_action is not None
+
+    def execute(self, context: LaunchContext) -> Optional[List[Action]]:
+        if self.lib_found():
+            return [self.__set_env_action]
+        return None
+
+    @staticmethod
+    def get_shared_lib_path(lib_name: str) -> Union[str, None]:
+        """
+        Get the full path to a given shared lib, if possible.
+
+        :param lib_name: the name of the shared library
+        :return: the full path if found, `None` otherwise
+        """
+        if not tracing_supported():
+            return None
+        (exit_code, output) = subprocess.getstatusoutput(f'whereis -b {lib_name}')
+        if exit_code != 0:
+            return None
+        # Output of whereis is
+        # <input_lib_name>: <full path, if found>
+        # Filter out empty strings, in case lib is not found
+        output_split = [split_part for split_part in output.split(':') if len(split_part) > 0]
+        if len(output_split) != 2:
+            return None
+        return output_split[1].strip()
+
+    def __repr__(self):
+        return (
+            'LdPreload('
+            f'lib_name={self.__lib_name}, '
+            f'lib found={self.lib_found()}, '
+            f'lib_path={self.__lib_path})'
+        )