strategy/common: introduce never_retry decorator

Introduce a decorator meant to decorate the strategy's transition() and
force() methods. It stores the original exception in the broken
attribute and raises a StrategyError from it. All subsequent calls to the
decorated method will lead to the same exception.

This prevents a strategy from subsequent use after an exception
happened, thus no cascading errors can happen.

Signed-off-by: Bastian Krause <bst@pengutronix.de>

Author: Bastian-Krause

labgrid/strategy/__init__.py

@@ -1,4 +1,4 @@
-from .common import Strategy, StrategyError
+from .common import Strategy, StrategyError, never_retry
 from .bareboxstrategy import BareboxStrategy
 from .shellstrategy import ShellStrategy
 from .ubootstrategy import UBootStrategy

labgrid/strategy/common.py

@@ -1,9 +1,33 @@
+import functools
+
 import attr
 
 from ..binding import BindingError
 from ..driver import Driver
 
 
+def never_retry(func):
+    """
+    Strategy method decorator storing the original exception in strategy.broken and raising a
+    StrategyError from it. All subsequent calls to the decorated method will lead to the same
+    exception.
+    """
+    @functools.wraps(func)
+    def wrapper(self, *args, **kwargs):
+        if self.broken:
+            # a previous call broke the strategy, raise the original exception again
+            raise StrategyError(f"{self.__class__.__name__} is in broken state") from self.broken
+
+        try:
+            return func(self, *args, **kwargs)
+        except Exception as e:
+            # store original exception and raise StrategyError from it
+            self.broken = e
+            raise StrategyError(f"{self.__class__.__name__} is in broken state") from self.broken
+
+    return wrapper
+
+
 @attr.s(eq=False)
 class StrategyError(Exception):
     msg = attr.ib(validator=attr.validators.instance_of(str))