"""
Debugging utilities for constructs
"""
import sys
import traceback
import pdb
import inspect
from construct.core import Construct, Subconstruct
from construct.lib import HexString, Container, ListContainer
class Probe(Construct):
"""
A probe: dumps the context, stack frames, and stream content to the screen
to aid the debugging process.
.. seealso:: :class:`Debugger`.
:param name: the display name
:param show_stream: whether or not to show stream contents. default is True. the stream must be seekable.
:param show_context: whether or not to show the context. default is True.
:param show_stack: whether or not to show the upper stack frames. default is True.
:param stream_lookahead: the number of bytes to dump when show_stack is set. default is 100.
Example::
Struct("foo",
UBInt8("a"),
Probe("between a and b"),
UBInt8("b"),
)
"""
__slots__ = [
"printname", "show_stream", "show_context", "show_stack",
"stream_lookahead"
]
counter = 0
def __init__(self, name = None, show_stream = True,
show_context = True, show_stack = True,
stream_lookahead = 100):
Construct.__init__(self, None)
if name is None:
Probe.counter += 1
name = "<unnamed %d>" % (Probe.counter,)
self.printname = name
self.show_stream = show_stream
self.show_context = show_context
self.show_stack = show_stack
self.stream_lookahead = stream_lookahead
def __repr__(self):
return "%s(%r)" % (self.__class__.__name__, self.printname)
def _parse(self, stream, context):
self.printout(stream, context)
def _build(self, obj, stream, context):
self.printout(stream, context)
def _sizeof(self, context):
return 0
def printout(self, stream, context):
obj = Container()
if self.show_stream:
obj.stream_position = stream.tell()
follows = stream.read(self.stream_lookahead)
if not follows:
obj.following_stream_data = "EOF reached"
else:
stream.seek(-len(follows), 1)
obj.following_stream_data = HexString(follows)
print("")
if self.show_context:
obj.context = context
if self.show_stack:
obj.stack = ListContainer()
frames = [s[0] for s in inspect.stack()][1:-1]
frames.reverse()
for f in frames:
a = Container()
a.__update__(f.f_locals)
obj.stack.append(a)
print("=" * 80)
print("Probe %s" % (self.printname,))
print(obj)
print("=" * 80)
class Debugger(Subconstruct):
"""
A pdb-based debugger. When an exception occurs in the subcon, a debugger
will appear and allow you to debug the error (and even fix on-the-fly).
:param subcon: the subcon to debug
Example::
Debugger(
Enum(UBInt8("foo"),
a = 1,
b = 2,
c = 3
)
)
"""
__slots__ = ["retval"]
def _parse(self, stream, context):
try:
return self.subcon._parse(stream, context)
except Exception:
self.retval = NotImplemented
self.handle_exc("(you can set the value of 'self.retval', "
"which will be returned)")
if self.retval is NotImplemented:
raise
else:
return self.retval
def _build(self, obj, stream, context):
try:
self.subcon._build(obj, stream, context)
except Exception:
self.handle_exc()
def handle_exc(self, msg = None):
print("=" * 80)
print("Debugging exception of %s:" % (self.subcon,))
print("".join(traceback.format_exception(*sys.exc_info())[1:]))
if msg:
print(msg)
pdb.post_mortem(sys.exc_info()[2])
print("=" * 80)
