Shell script handlers by freq (#1166)

Handlers for per-boot/per-instance/per-once multipart MIME

Add handlers for adding scripts to userdata that can be run at various
frequencies. Scripts of type x-shellscript-per-boot,
x-shellscript-per-instance, or x-shellscript-per-once can be added
to a multipart MIME userdata message as part of instance userdata.
These scripts will then be added to the appropriate per-boot,
per-instance, or per-once directory in /var/lib/cloud/scripts/
during processing of userdata.

1 files changed, 62 insertions, 0 deletions

diff --git a/cloudinit/handlers/shell_script_by_frequency.py b/cloudinit/handlers/shell_script_by_frequency.py
new file mode 100644
index 00000000..923cca57
--- /dev/null
+++ b/cloudinit/handlers/shell_script_by_frequency.py
@@ -0,0 +1,62 @@
+import os
+
+from cloudinit import log, util
+from cloudinit.handlers import Handler
+from cloudinit.settings import PER_ALWAYS, PER_INSTANCE, PER_ONCE
+
+LOG = log.getLogger(__name__)
+
+# cloudinit/settings.py defines PER_*** frequency constants. It makes sense to
+# use them here, instead of hardcodes, and map them to the 'per-***' frequency-
+# specific folders in /v/l/c/scripts. It might make sense to expose this at a
+# higher level or in a more general module -- eg maybe in cloudinit/settings.py
+# itself -- but for now it's here.
+path_map = {
+    PER_ALWAYS: "per-boot",
+    PER_INSTANCE: "per-instance",
+    PER_ONCE: "per-once",
+}
+
+
+def get_mime_type_by_frequency(freq):
+    mime_type = f"text/x-shellscript-{path_map[freq]}"
+    return mime_type
+
+
+def get_script_folder_by_frequency(freq, scripts_dir):
+    """Return the frequency-specific subfolder for a given frequency constant
+    and parent folder."""
+    freqPath = path_map[freq]
+    folder = os.path.join(scripts_dir, freqPath)
+    return folder
+
+
+def write_script_by_frequency(script_path, payload, frequency, scripts_dir):
+    """Given a filename, a payload, a frequency, and a scripts folder, write
+    the payload to the correct frequency-specific path"""
+    filename = os.path.basename(script_path)
+    filename = util.clean_filename(filename)
+    folder = get_script_folder_by_frequency(frequency, scripts_dir)
+    path = os.path.join(folder, filename)
+    payload = util.dos2unix(payload)
+    util.write_file(path, payload, 0o700)
+
+
+class ShellScriptByFreqPartHandler(Handler):
+    """Common base class for the frequency-specific script handlers."""
+
+    def __init__(self, script_frequency, paths, **_kwargs):
+        Handler.__init__(self, PER_ALWAYS)
+        self.prefixes = [get_mime_type_by_frequency(script_frequency)]
+        self.script_frequency = script_frequency
+        self.scripts_dir = paths.get_cpath("scripts")
+        if "script_path" in _kwargs:
+            self.scripts_dir = paths.get_cpath(_kwargs["script_path"])
+
+    def handle_part(self, data, ctype, script_path, payload, frequency):
+        if script_path is not None:
+            filename = os.path.basename(script_path)
+            filename = util.clean_filename(filename)
+            write_script_by_frequency(
+                script_path, payload, self.script_frequency, self.scripts_dir
+            )