From 1bb62eed4dd97067ae35e922db3669701dc0a3fe Mon Sep 17 00:00:00 2001
From: Brad Warren <bradmw@umich.edu>
Date: Thu, 10 Sep 2015 22:35:44 -0400
Subject: [PATCH] Started crash recovery mechanism

---
 letsencrypt/error_handler.py | 46 ++++++++++++++++++++++++++++++++++++
 letsencrypt/interfaces.py    | 11 +++++++++
 2 files changed, 57 insertions(+)
 create mode 100644 letsencrypt/error_handler.py

diff --git a/letsencrypt/error_handler.py b/letsencrypt/error_handler.py
new file mode 100644
index 000000000..884c73927
--- /dev/null
+++ b/letsencrypt/error_handler.py
@@ -0,0 +1,46 @@
+"""Registers and calls cleanup functions in case of an error."""
+import os
+import signal
+
+
+_SIGNALS = [signal.SIGTERM] if os.name == "nt" else
+           [signal.SIGTERM, signal.SIGHUP, signal.SIGQUIT,
+            signal.SIGXCPU, signal.SIGXFSZ, signal.SIGPWR,]
+
+
+class ErrorHandler():
+    """Registers and calls cleanup functions in case of an error."""
+    def __init__(self, func=None):
+        self.funcs = []
+        if func:
+            self.funcs.append(func)
+
+    def __enter__(self):
+        self.set_signal_handlers()
+
+    def __exit__(self, exec_type, exec_value, traceback):
+        if exec_value is not None:
+            self.cleanup()
+        self.reset_signal_handlers()
+
+    def register(self, func):
+        """Registers func to be called if an error occurs."""
+        self.funcs.append(func)
+    
+    def cleanup(self):
+        """Calls all registered functions."""
+        while self.funcs:
+            self.funcs.pop()()
+
+    def set_signal_handlers(self):
+        for signal_type in _SIGNALS:
+            signal.signal(signal_type, self._signal_handler)
+
+    def reset_signal_handlers(self):
+        for signal_type in _SIGNALS:
+            signal.signal(signal_type, signal.SIG_DFL)
+
+    def _signal_handler(self, signum, frame):
+        self.cleanup()
+        signal.signal(signal_type, signal.SIG_DFL)
+        os.kill(os.getpid(), signum)
diff --git a/letsencrypt/interfaces.py b/letsencrypt/interfaces.py
index f330e28ce..653b5685b 100644
--- a/letsencrypt/interfaces.py
+++ b/letsencrypt/interfaces.py
@@ -322,6 +322,17 @@ class IInstaller(IPlugin):
 
         """
 
+    def recovery_routine(self):
+        """Revert configuration to most recent finalized checkpoint.
+
+        Remove all changes (temporary and permanent) that have not been
+        finalized. This is useful to protect against crashes and other
+        execution interruptions.
+
+        :raises .errors.PluginError: If unable to recover the configuration
+
+        """
+
     def view_config_changes():
         """Display all of the LE config changes.