def seek_temporary(stream: IO[Any], path: str, offset: int) -> Iterator[None]:
'''
Context manager which seeks to the specified offset on entering,
and seeks back to the original offset on exit
'''
fallback = stream_tell(stream, path)
stream_seek(stream, offset, 0, path)
yield
stream_seek(stream, fallback, 0, path)
def _parse(self, stream, context, path):
# Get Index if we are in an Array, Sequence, ...
if hasattr(context, "_index"):
index = context._index
else:
index = None
offset_start = cs.stream_tell(stream, path)
obj = self.subcon._parsereport(stream, context, path) # type: ignore
offset_end = cs.stream_tell(stream, path)
gui_metadata = GuiMetaData(
offset_start=offset_start,
offset_end=offset_end,
length=offset_end - offset_start,
construct=self.subcon,
index=index,
context=context,
)
return add_gui_metadata(obj, gui_metadata)
def get_offset_in_outer_stream(stream, context, path):
'''
Tries to calculate the current offset in the outermost stream by traversing the context tree.
This is very likely to go completely wrong in many configurations;
right now it takes streams in other contexts and the :class:`Prefixed` type into account.
'''
offset = stream_tell(stream, path)
# collect offsets of enclosing streams by walking up the tree
prev_stream = stream
for c in iter_context_tree(context):
curr_stream = getattr(c, '_io', None)
if curr_stream is None:
break
# add to offset if stream changed
if curr_stream is not prev_stream:
offset += stream_tell(curr_stream, path)
prev_stream = curr_stream
# the Prefixed type writes the length _after_ building the subcon (which makes sense),
# but that also means that the current data will be written at [current offset] + [size of length field],
# which has to be taken into account as the stream's offset doesn't include the length field yet
stack = inspect.stack()
try:
for info in stack:
if info.function != '_build':
continue
local_self = info.frame.f_locals.get('self')
if isinstance(local_self, Prefixed):
offset += local_self.lengthfield.sizeof()
finally:
del stack # just to be safe, see https://docs.python.org/3/library/inspect.html#the-interpreter-stack
return offset
def stream_tell(stream, path):
return C.stream_tell(stream, path)
def _pad(self, stream, path):
v = self.modulus - 1
pos = stream_tell(stream, path)
newpos = (pos + v) & ~v
return newpos - pos