use constants for startswith in handlers. add strip_prefix_suffix.

Just cleans up some repeated strings into module constants + a util function to
do the boothook prefix cleanup (before writing).

cloudinit/handlers/boot_hook.py

@@ -29,6 +29,7 @@ from cloudinit import util
 from cloudinit.settings import (PER_ALWAYS)
 
 LOG = logging.getLogger(__name__)
+BOOTHOOK_PREFIX = "#cloud-boothook"
 
 
 class BootHookPartHandler(handlers.Handler):
@@ -41,19 +42,15 @@ class BootHookPartHandler(handlers.Handler):
 
     def list_types(self):
         return [
-            handlers.type_from_starts_with("#cloud-boothook"),
+            handlers.type_from_starts_with(BOOTHOOK_PREFIX),
         ]
 
     def _write_part(self, payload, filename):
         filename = util.clean_filename(filename)
-        payload = util.dos2unix(payload)
-        prefix = "#cloud-boothook"
-        start = 0
-        if payload.startswith(prefix):
-            start = len(prefix) + 1
         filepath = os.path.join(self.boothook_dir, filename)
-        contents = payload[start:]
-        util.write_file(filepath, contents, 0700)
+        contents = util.strip_prefix_suffix(util.dos2unix(payload),
+                                            prefix=BOOTHOOK_PREFIX)
+        util.write_file(filepath, contents.lstrip(), 0700)
         return filepath
 
     def handle_part(self, _data, ctype, filename,  # pylint: disable=W0221

cloudinit/handlers/cloud_config.py

@@ -49,6 +49,7 @@ MERGE_HEADER = 'Merge-Type'
 #
 # This gets loaded into yaml with final result {'a': 22}
 DEF_MERGERS = mergers.string_extract_mergers('dict(replace)+list()+str()')
+CLOUD_PREFIX = "#cloud-config"
 
 
 class CloudConfigPartHandler(handlers.Handler):
@@ -60,7 +61,7 @@ class CloudConfigPartHandler(handlers.Handler):
 
     def list_types(self):
         return [
-            handlers.type_from_starts_with("#cloud-config"),
+            handlers.type_from_starts_with(CLOUD_PREFIX),
         ]
 
     def _write_cloud_config(self):
@@ -78,7 +79,7 @@ class CloudConfigPartHandler(handlers.Handler):
         if self.cloud_buf is not None:
             # Something was actually gathered....
             lines = [
-                "#cloud-config",
+                CLOUD_PREFIX,
                 '',
             ]
             lines.extend(file_lines)

cloudinit/handlers/shell_script.py

@@ -29,6 +29,7 @@ from cloudinit import util
 from cloudinit.settings import (PER_ALWAYS)
 
 LOG = logging.getLogger(__name__)
+SHELL_PREFIX = "#!"
 
 
 class ShellScriptPartHandler(handlers.Handler):
@@ -38,7 +39,7 @@ class ShellScriptPartHandler(handlers.Handler):
 
     def list_types(self):
         return [
-            handlers.type_from_starts_with("#!"),
+            handlers.type_from_starts_with(SHELL_PREFIX),
         ]
 
     def handle_part(self, _data, ctype, filename,  # pylint: disable=W0221

cloudinit/handlers/upstart_job.py

@@ -31,6 +31,7 @@ from cloudinit import util
 from cloudinit.settings import (PER_INSTANCE)
 
 LOG = logging.getLogger(__name__)
+UPSTART_PREFIX = "#upstart-job"
 
 
 class UpstartJobPartHandler(handlers.Handler):
@@ -40,7 +41,7 @@ class UpstartJobPartHandler(handlers.Handler):
 
     def list_types(self):
         return [
-            handlers.type_from_starts_with("#upstart-job"),
+            handlers.type_from_starts_with(UPSTART_PREFIX),
         ]
 
     def handle_part(self, _data, ctype, filename,  # pylint: disable=W0221

cloudinit/util.py

@@ -1530,6 +1530,14 @@ def shellify(cmdlist, add_header=True):
     return content
 
 
+def strip_prefix_suffix(line, prefix=None, suffix=None):
+    if prefix and line.startswith(prefix):
+        line = line[len(prefix):]
+    if suffix and line.endswith(suffix):
+        line = line[:-len(suffix)]
+    return line
+
+
 def is_container():
     """
     Checks to see if this code running in a container of some sort