1 files changed, 57 insertions, 0 deletions
diff --git a/cloudinit/subp.py b/cloudinit/subp.py
new file mode 100644
index 00000000..0ad09306
--- /dev/null
+++ b/cloudinit/subp.py
@@ -0,0 +1,57 @@
+# This file is part of cloud-init. See LICENSE file for license information.
+"""Common utility functions for interacting with subprocess."""
+
+# TODO move subp shellify and runparts related functions out of util.py
+
+import logging
+
+LOG = logging.getLogger(__name__)
+
+
+def prepend_base_command(base_command, commands):
+    """Ensure user-provided commands start with base_command; warn otherwise.
+
+    Each command is either a list or string. Perform the following:
+       - If the command is a list, pop the first element if it is None
+       - If the command is a list, insert base_command as the first element if
+         not present.
+       - When the command is a string not starting with 'base-command', warn.
+
+    Allow flexibility to provide non-base-command environment/config setup if
+    needed.
+
+    @commands: List of commands. Each command element is a list or string.
+
+    @return: List of 'fixed up' commands.
+    @raise: TypeError on invalid config item type.
+    """
+    warnings = []
+    errors = []
+    fixed_commands = []
+    for command in commands:
+        if isinstance(command, list):
+            if command[0] is None:  # Avoid warnings by specifying None
+                command = command[1:]
+            elif command[0] != base_command:  # Automatically prepend
+                command.insert(0, base_command)
+        elif isinstance(command, str):
+            if not command.startswith('%s ' % base_command):
+                warnings.append(command)
+        else:
+            errors.append(str(command))
+            continue
+        fixed_commands.append(command)
+
+    if warnings:
+        LOG.warning(
+            'Non-%s commands in %s config:\n%s',
+            base_command, base_command, '\n'.join(warnings))
+    if errors:
+        raise TypeError(
+            'Invalid {name} config.'
+            ' These commands are not a string or list:\n{errors}'.format(
+                name=base_command, errors='\n'.join(errors)))
+    return fixed_commands
+
+
+# vi: ts=4 expandtab