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"""
Analogous to atexit, this module allows the programmer to register functions to
be run if an unhandled exception occurs.
"""
from __future__ import absolute_import
from __future__ import division
import sys
import threading
import traceback
from pwnlib.context import context
__all__ = ['register', 'unregister']
_lock = threading.Lock()
_ident = 0
_handlers = {}
def register(func, *args, **kwargs):
"""register(func, *args, **kwargs)
Registers a function to be called when an unhandled exception occurs. The
function will be called with positional arguments `args` and keyword
arguments `kwargs`, i.e. ``func(*args, **kwargs)``. The current `context`
is recorded and will be the one used when the handler is run.
E.g. to suppress logging output from an exception-handler one could write::
with context.local(log_level = 'error'):
atexception.register(handler)
An identifier is returned which can be used to unregister the
exception-handler.
This function can be used as a decorator::
@atexception.register
def handler():
...
Notice however that this will bind ``handler`` to the identifier and not the
actual exception-handler. The exception-handler can then be unregistered
with::
atexception.unregister(handler)
This function is thread safe.
"""
global _ident
with _lock:
ident = _ident
_ident += 1
_handlers[ident] = (func, args, kwargs, vars(context))
return ident
def unregister(func):
"""unregister(func)
Remove `func` from the collection of registered functions. If `func` isn't
registered this is a no-op.
"""
if func in _handlers:
del _handlers[func]
def _run_handlers():
"""_run_handlers()
Run registered handlers. They run in the reverse order of which they were
registered.
If a handler raises an exception, it will be printed but nothing else
happens, i.e. other handlers will be run.
"""
for _ident, (func, args, kwargs, ctx) in \
sorted(_handlers.items(), reverse = True):
try:
with context.local():
context.clear()
context.update(**ctx)
func(*args, **kwargs)
except SystemExit:
pass
except Exception:
# extract the current exception and rewind the traceback to where it
# originated
typ, val, tb = sys.exc_info()
traceback.print_exception(typ, val, tb.tb_next)
# we rely on the existing excepthook to print exceptions
_oldhook = getattr(sys, 'excepthook', None)
def _newhook(typ, val, tb):
"""_newhook(typ, val, tb)
Our excepthook replacement. First the original hook is called to print the
exception, then each handler is called.
"""
if _oldhook:
_oldhook(typ, val, tb)
if _run_handlers:
_run_handlers()
sys.excepthook = _newhook
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