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# -*- test-case-name: twisted.test.test_failure -*-
# See also test suite twisted.test.test_pbfailure
# Copyright (c) Twisted Matrix Laboratories.
# See LICENSE for details.
"""
Asynchronous-friendly error mechanism.
See L{Failure}.
"""
# System Imports
import builtins
import copy
import inspect
import linecache
import sys
from inspect import getmro
from io import StringIO
from typing import Callable, NoReturn, TypeVar
import opcode
from twisted.python import reflect
_T_Callable = TypeVar("_T_Callable", bound=Callable[..., object])
count = 0
traceupLength = 4
class DefaultException(Exception):
pass
def format_frames(frames, write, detail="default"):
"""
Format and write frames.
@param frames: is a list of frames as used by Failure.frames, with
each frame being a list of
(funcName, fileName, lineNumber, locals.items(), globals.items())
@type frames: list
@param write: this will be called with formatted strings.
@type write: callable
@param detail: Four detail levels are available:
default, brief, verbose, and verbose-vars-not-captured.
C{Failure.printDetailedTraceback} uses the latter when the caller asks
for verbose, but no vars were captured, so that an explicit warning
about the missing data is shown.
@type detail: string
"""
if detail not in ("default", "brief", "verbose", "verbose-vars-not-captured"):
raise ValueError(
"Detail must be default, brief, verbose, or "
"verbose-vars-not-captured. (not %r)" % (detail,)
)
w = write
if detail == "brief":
for method, filename, lineno, localVars, globalVars in frames:
w(f"{filename}:{lineno}:{method}\n")
elif detail == "default":
for method, filename, lineno, localVars, globalVars in frames:
w(f' File "{filename}", line {lineno}, in {method}\n')
w(" %s\n" % linecache.getline(filename, lineno).strip())
elif detail == "verbose-vars-not-captured":
for method, filename, lineno, localVars, globalVars in frames:
w("%s:%d: %s(...)\n" % (filename, lineno, method))
w(" [Capture of Locals and Globals disabled (use captureVars=True)]\n")
elif detail == "verbose":
for method, filename, lineno, localVars, globalVars in frames:
w("%s:%d: %s(...)\n" % (filename, lineno, method))
w(" [ Locals ]\n")
# Note: the repr(val) was (self.pickled and val) or repr(val)))
for name, val in localVars:
w(f" {name} : {repr(val)}\n")
w(" ( Globals )\n")
for name, val in globalVars:
w(f" {name} : {repr(val)}\n")
# slyphon: i have a need to check for this value in trial
# so I made it a module-level constant
EXCEPTION_CAUGHT_HERE = "--- <exception caught here> ---"
class NoCurrentExceptionError(Exception):
"""
Raised when trying to create a Failure from the current interpreter
exception state and there is no current exception state.
"""
def _Traceback(stackFrames, tbFrames):
"""
Construct a fake traceback object using a list of frames.
It should have the same API as stdlib to allow interaction with
other tools.
@param stackFrames: [(methodname, filename, lineno, locals, globals), ...]
@param tbFrames: [(methodname, filename, lineno, locals, globals), ...]
"""
assert len(tbFrames) > 0, "Must pass some frames"
# We deliberately avoid using recursion here, as the frames list may be
# long.
# 'stackFrames' is a list of frames above (ie, older than) the point the
# exception was caught, with oldest at the start. Start by building these
# into a linked list of _Frame objects (with the f_back links pointing back
# towards the oldest frame).
stack = None
for sf in stackFrames:
stack = _Frame(sf, stack)
# 'tbFrames' is a list of frames from the point the exception was caught,
# down to where it was thrown, with the oldest at the start. Add these to
# the linked list of _Frames, but also wrap each one with a _Traceback
# frame which is linked in the opposite direction (towards the newest
# frame).
stack = _Frame(tbFrames[0], stack)
firstTb = tb = _TracebackFrame(stack)
for sf in tbFrames[1:]:
stack = _Frame(sf, stack)
tb.tb_next = _TracebackFrame(stack)
tb = tb.tb_next
# Return the first _TracebackFrame.
return firstTb
# The set of attributes for _TracebackFrame, _Frame and _Code were taken from
# https://docs.python.org/3.11/library/inspect.html Other Pythons may have a
# few more attributes that should be added if needed.
class _TracebackFrame:
"""
Fake traceback object which can be passed to functions in the standard
library L{traceback} module.
"""
def __init__(self, frame):
"""
@param frame: _Frame object
"""
self.tb_frame = frame
self.tb_lineno = frame.f_lineno
self.tb_lasti = frame.f_lasti
self.tb_next = None
class _Frame:
"""
A fake frame object, used by L{_Traceback}.
@ivar f_code: fake L{code<types.CodeType>} object
@ivar f_lineno: line number
@ivar f_globals: fake f_globals dictionary (usually empty)
@ivar f_locals: fake f_locals dictionary (usually empty)
@ivar f_back: previous stack frame (towards the caller)
"""
def __init__(self, frameinfo, back):
"""
@param frameinfo: (methodname, filename, lineno, locals, globals)
@param back: previous (older) stack frame
@type back: C{frame}
"""
name, filename, lineno, localz, globalz = frameinfo
self.f_code = _Code(name, filename)
self.f_lineno = lineno
self.f_globals = dict(globalz or {})
self.f_locals = dict(localz or {})
self.f_back = back
self.f_lasti = 0
self.f_builtins = vars(builtins).copy()
self.f_trace = None
class _Code:
"""
A fake code object, used by L{_Traceback} via L{_Frame}.
It is intended to have the same API as the stdlib code type to allow
interoperation with other tools based on that interface.
"""
def __init__(self, name, filename):
self.co_name = name
self.co_filename = filename
self.co_lnotab = b""
self.co_firstlineno = 0
self.co_argcount = 0
self.co_varnames = []
self.co_code = b""
self.co_cellvars = ()
self.co_consts = ()
self.co_flags = 0
self.co_freevars = ()
self.co_posonlyargcount = 0
self.co_kwonlyargcount = 0
self.co_names = ()
self.co_nlocals = 0
self.co_stacksize = 0
def co_positions(self):
return ((None, None, None, None),)
_inlineCallbacksExtraneous = []
def _extraneous(f: _T_Callable) -> _T_Callable:
"""
Mark the given callable as extraneous to inlineCallbacks exception
reporting; don't show these functions.
@param f: a function that you NEVER WANT TO SEE AGAIN in ANY TRACEBACK
reported by Failure.
@type f: function
@return: f
"""
_inlineCallbacksExtraneous.append(f.__code__)
return f
class Failure(BaseException):
"""
A basic abstraction for an error that has occurred.
This is necessary because Python's built-in error mechanisms are
inconvenient for asynchronous communication.
The C{stack} and C{frame} attributes contain frames. Each frame is a tuple
of (funcName, fileName, lineNumber, localsItems, globalsItems), where
localsItems and globalsItems are the contents of
C{locals().items()}/C{globals().items()} for that frame, or an empty tuple
if those details were not captured.
@ivar value: The exception instance responsible for this failure.
@ivar type: The exception's class.
@ivar stack: list of frames, innermost last, excluding C{Failure.__init__}.
@ivar frames: list of frames, innermost first.
"""
pickled = 0
stack = None
# The opcode of "yield" in Python bytecode. We need this in
# _findFailure in order to identify whether an exception was
# thrown by a throwExceptionIntoGenerator.
# on PY3, b'a'[0] == 97 while in py2 b'a'[0] == b'a' opcodes
# are stored in bytes so we need to properly account for this
# difference.
_yieldOpcode = opcode.opmap["YIELD_VALUE"]
def __init__(self, exc_value=None, exc_type=None, exc_tb=None, captureVars=False):
"""
Initialize me with an explanation of the error.
By default, this will use the current C{exception}
(L{sys.exc_info}()). However, if you want to specify a
particular kind of failure, you can pass an exception as an
argument.
If no C{exc_value} is passed, then an "original" C{Failure} will
be searched for. If the current exception handler that this
C{Failure} is being constructed in is handling an exception
raised by L{raiseException}, then this C{Failure} will act like
the original C{Failure}.
For C{exc_tb} only L{traceback} instances or L{None} are allowed.
If L{None} is supplied for C{exc_value}, the value of C{exc_tb} is
ignored, otherwise if C{exc_tb} is L{None}, it will be found from
execution context (ie, L{sys.exc_info}).
@param captureVars: if set, capture locals and globals of stack
frames. This is pretty slow, and makes no difference unless you
are going to use L{printDetailedTraceback}.
"""
global count
count = count + 1
self.count = count
self.type = self.value = tb = None
self.captureVars = captureVars
if isinstance(exc_value, str) and exc_type is None:
raise TypeError("Strings are not supported by Failure")
stackOffset = 0
if exc_value is None:
exc_value = self._findFailure()
if exc_value is None:
self.type, self.value, tb = sys.exc_info()
if self.type is None:
raise NoCurrentExceptionError()
stackOffset = 1
elif exc_type is None:
if isinstance(exc_value, Exception):
self.type = exc_value.__class__
else:
# Allow arbitrary objects.
self.type = type(exc_value)
self.value = exc_value
else:
self.type = exc_type
self.value = exc_value
if isinstance(self.value, Failure):
self._extrapolate(self.value)
return
if hasattr(self.value, "__failure__"):
# For exceptions propagated through coroutine-awaiting (see
# Deferred.send, AKA Deferred.__next__), which can't be raised as
# Failure because that would mess up the ability to except: them:
self._extrapolate(self.value.__failure__)
# Clean up the inherently circular reference established by storing
# the failure there. This should make the common case of a Twisted
# / Deferred-returning coroutine somewhat less hard on the garbage
# collector.
del self.value.__failure__
return
if tb is None:
if exc_tb:
tb = exc_tb
elif getattr(self.value, "__traceback__", None):
# Python 3
tb = self.value.__traceback__
frames = self.frames = []
stack = self.stack = []
# Added 2003-06-23 by Chris Armstrong. Yes, I actually have a
# use case where I need this traceback object, and I've made
# sure that it'll be cleaned up.
self.tb = tb
if tb:
f = tb.tb_frame
elif not isinstance(self.value, Failure):
# We don't do frame introspection since it's expensive,
# and if we were passed a plain exception with no
# traceback, it's not useful anyway
f = stackOffset = None
while stackOffset and f:
# This excludes this Failure.__init__ frame from the
# stack, leaving it to start with our caller instead.
f = f.f_back
stackOffset -= 1
# Keeps the *full* stack. Formerly in spread.pb.print_excFullStack:
#
# The need for this function arises from the fact that several
# PB classes have the peculiar habit of discarding exceptions
# with bareword "except:"s. This premature exception
# catching means tracebacks generated here don't tend to show
# what called upon the PB object.
while f:
if captureVars:
localz = f.f_locals.copy()
if f.f_locals is f.f_globals:
globalz = {}
else:
globalz = f.f_globals.copy()
for d in globalz, localz:
if "__builtins__" in d:
del d["__builtins__"]
localz = localz.items()
globalz = globalz.items()
else:
localz = globalz = ()
stack.insert(
0,
(
f.f_code.co_name,
f.f_code.co_filename,
f.f_lineno,
localz,
globalz,
),
)
f = f.f_back
while tb is not None:
f = tb.tb_frame
if captureVars:
localz = f.f_locals.copy()
if f.f_locals is f.f_globals:
globalz = {}
else:
globalz = f.f_globals.copy()
for d in globalz, localz:
if "__builtins__" in d:
del d["__builtins__"]
localz = list(localz.items())
globalz = list(globalz.items())
else:
localz = globalz = ()
frames.append(
(
f.f_code.co_name,
f.f_code.co_filename,
tb.tb_lineno,
localz,
globalz,
)
)
tb = tb.tb_next
if inspect.isclass(self.type) and issubclass(self.type, Exception):
parentCs = getmro(self.type)
self.parents = list(map(reflect.qual, parentCs))
else:
self.parents = [self.type]
def _extrapolate(self, otherFailure):
"""
Extrapolate from one failure into another, copying its stack frames.
@param otherFailure: Another L{Failure}, whose traceback information,
if any, should be preserved as part of the stack presented by this
one.
@type otherFailure: L{Failure}
"""
# Copy all infos from that failure (including self.frames).
self.__dict__ = copy.copy(otherFailure.__dict__)
# If we are re-throwing a Failure, we merge the stack-trace stored in
# the failure with the current exception's stack. This integrated with
# throwExceptionIntoGenerator and allows to provide full stack trace,
# even if we go through several layers of inlineCallbacks.
_, _, tb = sys.exc_info()
frames = []
while tb is not None:
f = tb.tb_frame
if f.f_code not in _inlineCallbacksExtraneous:
frames.append(
(f.f_code.co_name, f.f_code.co_filename, tb.tb_lineno, (), ())
)
tb = tb.tb_next
# Merging current stack with stack stored in the Failure.
frames.extend(self.frames)
self.frames = frames
def trap(self, *errorTypes):
"""
Trap this failure if its type is in a predetermined list.
This allows you to trap a Failure in an error callback. It will be
automatically re-raised if it is not a type that you expect.
The reason for having this particular API is because it's very useful
in Deferred errback chains::
def _ebFoo(self, failure):
r = failure.trap(Spam, Eggs)
print('The Failure is due to either Spam or Eggs!')
if r == Spam:
print('Spam did it!')
elif r == Eggs:
print('Eggs did it!')
If the failure is not a Spam or an Eggs, then the Failure will be
'passed on' to the next errback. In Python 2 the Failure will be
raised; in Python 3 the underlying exception will be re-raised.
@type errorTypes: L{Exception}
"""
error = self.check(*errorTypes)
if not error:
self.raiseException()
return error
def check(self, *errorTypes):
"""
Check if this failure's type is in a predetermined list.
@type errorTypes: list of L{Exception} classes or
fully-qualified class names.
@returns: the matching L{Exception} type, or None if no match.
"""
for error in errorTypes:
err = error
if inspect.isclass(error) and issubclass(error, Exception):
err = reflect.qual(error)
if err in self.parents:
return error
return None
def raiseException(self) -> NoReturn:
"""
raise the original exception, preserving traceback
information if available.
"""
raise self.value.with_traceback(self.tb)
@_extraneous
def throwExceptionIntoGenerator(self, g):
"""
Throw the original exception into the given generator,
preserving traceback information if available.
@return: The next value yielded from the generator.
@raise StopIteration: If there are no more values in the generator.
@raise anything else: Anything that the generator raises.
"""
# Note that the actual magic to find the traceback information
# is done in _findFailure.
return g.throw(self.value.with_traceback(self.tb))
@classmethod
def _findFailure(cls):
"""
Find the failure that represents the exception currently in context.
"""
tb = sys.exc_info()[-1]
if not tb:
return
secondLastTb = None
lastTb = tb
while lastTb.tb_next:
secondLastTb = lastTb
lastTb = lastTb.tb_next
lastFrame = lastTb.tb_frame
# NOTE: f_locals.get('self') is used rather than
# f_locals['self'] because psyco frames do not contain
# anything in their locals() dicts. psyco makes debugging
# difficult anyhow, so losing the Failure objects (and thus
# the tracebacks) here when it is used is not that big a deal.
# Handle raiseException-originated exceptions
if lastFrame.f_code is cls.raiseException.__code__:
return lastFrame.f_locals.get("self")
# Handle throwExceptionIntoGenerator-originated exceptions
# this is tricky, and differs if the exception was caught
# inside the generator, or above it:
# It is only really originating from
# throwExceptionIntoGenerator if the bottom of the traceback
# is a yield.
# Pyrex and Cython extensions create traceback frames
# with no co_code, but they can't yield so we know it's okay to
# just return here.
if (not lastFrame.f_code.co_code) or lastFrame.f_code.co_code[
lastTb.tb_lasti
] != cls._yieldOpcode:
return
# If the exception was caught above the generator.throw
# (outside the generator), it will appear in the tb (as the
# second last item):
if secondLastTb:
frame = secondLastTb.tb_frame
if frame.f_code is cls.throwExceptionIntoGenerator.__code__:
return frame.f_locals.get("self")
# If the exception was caught below the generator.throw
# (inside the generator), it will appear in the frames' linked
# list, above the top-level traceback item (which must be the
# generator frame itself, thus its caller is
# throwExceptionIntoGenerator).
frame = tb.tb_frame.f_back
if frame and frame.f_code is cls.throwExceptionIntoGenerator.__code__:
return frame.f_locals.get("self")
def __repr__(self) -> str:
return "<{} {}: {}>".format(
reflect.qual(self.__class__),
reflect.qual(self.type),
self.getErrorMessage(),
)
def __str__(self) -> str:
return "[Failure instance: %s]" % self.getBriefTraceback()
def __getstate__(self):
"""Avoid pickling objects in the traceback."""
if self.pickled:
return self.__dict__
c = self.__dict__.copy()
c["frames"] = [
[
v[0],
v[1],
v[2],
_safeReprVars(v[3]),
_safeReprVars(v[4]),
]
for v in self.frames
]
# Added 2003-06-23. See comment above in __init__
c["tb"] = None
if self.stack is not None:
# XXX: This is a band-aid. I can't figure out where these
# (failure.stack is None) instances are coming from.
c["stack"] = [
[
v[0],
v[1],
v[2],
_safeReprVars(v[3]),
_safeReprVars(v[4]),
]
for v in self.stack
]
c["pickled"] = 1
return c
def cleanFailure(self):
"""
Remove references to other objects, replacing them with strings.
On Python 3, this will also set the C{__traceback__} attribute of the
exception instance to L{None}.
"""
self.__dict__ = self.__getstate__()
if getattr(self.value, "__traceback__", None):
# Python 3
self.value.__traceback__ = None
def getTracebackObject(self):
"""
Get an object that represents this Failure's stack that can be passed
to traceback.extract_tb.
If the original traceback object is still present, return that. If this
traceback object has been lost but we still have the information,
return a fake traceback object (see L{_Traceback}). If there is no
traceback information at all, return None.
"""
if self.tb is not None:
return self.tb
elif len(self.frames) > 0:
return _Traceback(self.stack, self.frames)
else:
return None
def getErrorMessage(self) -> str:
"""
Get a string of the exception which caused this Failure.
"""
if isinstance(self.value, Failure):
return self.value.getErrorMessage()
return reflect.safe_str(self.value)
def getBriefTraceback(self) -> str:
io = StringIO()
self.printBriefTraceback(file=io)
return io.getvalue()
def getTraceback(self, elideFrameworkCode: int = 0, detail: str = "default") -> str:
io = StringIO()
self.printTraceback(
file=io, elideFrameworkCode=elideFrameworkCode, detail=detail
)
return io.getvalue()
def printTraceback(self, file=None, elideFrameworkCode=False, detail="default"):
"""
Emulate Python's standard error reporting mechanism.
@param file: If specified, a file-like object to which to write the
traceback.
@param elideFrameworkCode: A flag indicating whether to attempt to
remove uninteresting frames from within Twisted itself from the
output.
@param detail: A string indicating how much information to include
in the traceback. Must be one of C{'brief'}, C{'default'}, or
C{'verbose'}.
"""
if file is None:
from twisted.python import log
file = log.logerr
w = file.write
if detail == "verbose" and not self.captureVars:
# We don't have any locals or globals, so rather than show them as
# empty make the output explicitly say that we don't have them at
# all.
formatDetail = "verbose-vars-not-captured"
else:
formatDetail = detail
# Preamble
if detail == "verbose":
w(
"*--- Failure #%d%s---\n"
% (self.count, (self.pickled and " (pickled) ") or " ")
)
elif detail == "brief":
if self.frames:
hasFrames = "Traceback"
else:
hasFrames = "Traceback (failure with no frames)"
w(
"%s: %s: %s\n"
% (hasFrames, reflect.safe_str(self.type), reflect.safe_str(self.value))
)
else:
w("Traceback (most recent call last):\n")
# Frames, formatted in appropriate style
if self.frames:
if not elideFrameworkCode:
format_frames(self.stack[-traceupLength:], w, formatDetail)
w(f"{EXCEPTION_CAUGHT_HERE}\n")
format_frames(self.frames, w, formatDetail)
elif not detail == "brief":
# Yeah, it's not really a traceback, despite looking like one...
w("Failure: ")
# Postamble, if any
if not detail == "brief":
w(f"{reflect.qual(self.type)}: {reflect.safe_str(self.value)}\n")
# Chaining
if isinstance(self.value, Failure):
# TODO: indentation for chained failures?
file.write(" (chained Failure)\n")
self.value.printTraceback(file, elideFrameworkCode, detail)
if detail == "verbose":
w("*--- End of Failure #%d ---\n" % self.count)
def printBriefTraceback(self, file=None, elideFrameworkCode=0):
"""
Print a traceback as densely as possible.
"""
self.printTraceback(file, elideFrameworkCode, detail="brief")
def printDetailedTraceback(self, file=None, elideFrameworkCode=0):
"""
Print a traceback with detailed locals and globals information.
"""
self.printTraceback(file, elideFrameworkCode, detail="verbose")
def _safeReprVars(varsDictItems):
"""
Convert a list of (name, object) pairs into (name, repr) pairs.
L{twisted.python.reflect.safe_repr} is used to generate the repr, so no
exceptions will be raised by faulty C{__repr__} methods.
@param varsDictItems: a sequence of (name, value) pairs as returned by e.g.
C{locals().items()}.
@returns: a sequence of (name, repr) pairs.
"""
return [(name, reflect.safe_repr(obj)) for (name, obj) in varsDictItems]
# slyphon: make post-morteming exceptions tweakable
DO_POST_MORTEM = True
def _debuginit(
self,
exc_value=None,
exc_type=None,
exc_tb=None,
captureVars=False,
Failure__init__=Failure.__init__,
):
"""
Initialize failure object, possibly spawning pdb.
"""
if (exc_value, exc_type, exc_tb) == (None, None, None):
exc = sys.exc_info()
if not exc[0] == self.__class__ and DO_POST_MORTEM:
try:
strrepr = str(exc[1])
except BaseException:
strrepr = "broken str"
print(
"Jumping into debugger for post-mortem of exception '{}':".format(
strrepr
)
)
import pdb
pdb.post_mortem(exc[2])
Failure__init__(self, exc_value, exc_type, exc_tb, captureVars)
def startDebugMode():
"""
Enable debug hooks for Failures.
"""
Failure.__init__ = _debuginit