def SeqOfOne(name, *args, **kw):
"""a sequence of one element. only the first element is meaningful, the
rest are discarded
* name - the name of the sequence
* args - subconstructs
* kw - any keyword arguments to Sequence
"""
return IndexingAdapter(Sequence(name, *args, **kw), index=0)
def SeqOfOne(name, *args, **kw):
r"""A sequence of one element. only the first element is meaningful, the
rest are discarded
:param name: the name of the sequence
:param \*args: subconstructs
:param \*\*kw: any keyword arguments to Sequence
"""
return IndexingAdapter(Sequence(name, *args, **kw), index=0)
def PrefixedArray(subcon, length_field=UBInt8("length")):
"""an array prefixed by a length field.
* subcon - the subcon to be repeated
* length_field - a construct returning an integer
"""
return LengthValueAdapter(
Sequence(subcon.name,
length_field,
Array(lambda ctx: ctx[length_field.name], subcon),
nested=False))
def PrefixedArray(subcon, length_field=UBInt8("length")):
"""An array prefixed by a length field.
:param subcon: the subcon to be repeated
:param length_field: a construct returning an integer
"""
def _length(ctx):
if issubclass(ctx.__class__, (list, tuple)):
return len(ctx)
return ctx[length_field.name]
return LengthValueAdapter(
Sequence(subcon.name,
length_field,
Array(_length, subcon),
nested=False))
def PascalString(name, length_field=UBInt8("length"), encoding=None):
r"""
A length-prefixed string.
``PascalString`` is named after the string types of Pascal, which are
length-prefixed. Lisp strings also follow this convention.
The length field will appear in the same ``Container`` as the
``PascalString``, with the given name.
:param name: name
:param length_field: a field which will store the length of the string
:param encoding: encoding (e.g. "utf8") or None for no encoding
Example::
>>> foo = PascalString("foo")
>>> foo.parse("\x05hello")
'hello'
>>> foo.build("hello world")
'\x0bhello world'
>>>
>>> foo = PascalString("foo", length_field = UBInt16("length"))
>>> foo.parse("\x00\x05hello")
'hello'
>>> foo.build("hello")
'\x00\x05hello'
"""
return StringAdapter(
LengthValueAdapter(
Sequence(
name,
length_field,
Field("data", lambda ctx: ctx[length_field.name]),
)),
encoding=encoding,
)