221 lines
6.6 KiB
Python
221 lines
6.6 KiB
Python
"""sstruct.py -- SuperStruct
|
|
|
|
Higher level layer on top of the struct module, enabling to
|
|
bind names to struct elements. The interface is similar to
|
|
struct, except the objects passed and returned are not tuples
|
|
(or argument lists), but dictionaries or instances.
|
|
|
|
Just like struct, we use fmt strings to describe a data
|
|
structure, except we use one line per element. Lines are
|
|
separated by newlines or semi-colons. Each line contains
|
|
either one of the special struct characters ('@', '=', '<',
|
|
'>' or '!') or a 'name:formatchar' combo (eg. 'myFloat:f').
|
|
Repetitions, like the struct module offers them are not useful
|
|
in this context, except for fixed length strings (eg. 'myInt:5h'
|
|
is not allowed but 'myString:5s' is). The 'x' fmt character
|
|
(pad byte) is treated as 'special', since it is by definition
|
|
anonymous. Extra whitespace is allowed everywhere.
|
|
|
|
The sstruct module offers one feature that the "normal" struct
|
|
module doesn't: support for fixed point numbers. These are spelled
|
|
as "n.mF", where n is the number of bits before the point, and m
|
|
the number of bits after the point. Fixed point numbers get
|
|
converted to floats.
|
|
|
|
pack(fmt, object):
|
|
'object' is either a dictionary or an instance (or actually
|
|
anything that has a __dict__ attribute). If it is a dictionary,
|
|
its keys are used for names. If it is an instance, it's
|
|
attributes are used to grab struct elements from. Returns
|
|
a string containing the data.
|
|
|
|
unpack(fmt, data, object=None)
|
|
If 'object' is omitted (or None), a new dictionary will be
|
|
returned. If 'object' is a dictionary, it will be used to add
|
|
struct elements to. If it is an instance (or in fact anything
|
|
that has a __dict__ attribute), an attribute will be added for
|
|
each struct element. In the latter two cases, 'object' itself
|
|
is returned.
|
|
|
|
unpack2(fmt, data, object=None)
|
|
Convenience function. Same as unpack, except data may be longer
|
|
than needed. The returned value is a tuple: (object, leftoverdata).
|
|
|
|
calcsize(fmt)
|
|
like struct.calcsize(), but uses our own fmt strings:
|
|
it returns the size of the data in bytes.
|
|
"""
|
|
|
|
from fontTools.misc.fixedTools import fixedToFloat as fi2fl, floatToFixed as fl2fi
|
|
from fontTools.misc.textTools import tobytes, tostr
|
|
import struct
|
|
import re
|
|
|
|
__version__ = "1.2"
|
|
__copyright__ = "Copyright 1998, Just van Rossum <just@letterror.com>"
|
|
|
|
|
|
class Error(Exception):
|
|
pass
|
|
|
|
|
|
def pack(fmt, obj):
|
|
formatstring, names, fixes = getformat(fmt, keep_pad_byte=True)
|
|
elements = []
|
|
if not isinstance(obj, dict):
|
|
obj = obj.__dict__
|
|
for name in names:
|
|
value = obj[name]
|
|
if name in fixes:
|
|
# fixed point conversion
|
|
value = fl2fi(value, fixes[name])
|
|
elif isinstance(value, str):
|
|
value = tobytes(value)
|
|
elements.append(value)
|
|
data = struct.pack(*(formatstring,) + tuple(elements))
|
|
return data
|
|
|
|
|
|
def unpack(fmt, data, obj=None):
|
|
if obj is None:
|
|
obj = {}
|
|
data = tobytes(data)
|
|
formatstring, names, fixes = getformat(fmt)
|
|
if isinstance(obj, dict):
|
|
d = obj
|
|
else:
|
|
d = obj.__dict__
|
|
elements = struct.unpack(formatstring, data)
|
|
for i in range(len(names)):
|
|
name = names[i]
|
|
value = elements[i]
|
|
if name in fixes:
|
|
# fixed point conversion
|
|
value = fi2fl(value, fixes[name])
|
|
elif isinstance(value, bytes):
|
|
try:
|
|
value = tostr(value)
|
|
except UnicodeDecodeError:
|
|
pass
|
|
d[name] = value
|
|
return obj
|
|
|
|
|
|
def unpack2(fmt, data, obj=None):
|
|
length = calcsize(fmt)
|
|
return unpack(fmt, data[:length], obj), data[length:]
|
|
|
|
|
|
def calcsize(fmt):
|
|
formatstring, names, fixes = getformat(fmt)
|
|
return struct.calcsize(formatstring)
|
|
|
|
|
|
# matches "name:formatchar" (whitespace is allowed)
|
|
_elementRE = re.compile(
|
|
r"\s*" # whitespace
|
|
r"([A-Za-z_][A-Za-z_0-9]*)" # name (python identifier)
|
|
r"\s*:\s*" # whitespace : whitespace
|
|
r"([xcbB?hHiIlLqQfd]|" # formatchar...
|
|
r"[0-9]+[ps]|" # ...formatchar...
|
|
r"([0-9]+)\.([0-9]+)(F))" # ...formatchar
|
|
r"\s*" # whitespace
|
|
r"(#.*)?$" # [comment] + end of string
|
|
)
|
|
|
|
# matches the special struct fmt chars and 'x' (pad byte)
|
|
_extraRE = re.compile(r"\s*([x@=<>!])\s*(#.*)?$")
|
|
|
|
# matches an "empty" string, possibly containing whitespace and/or a comment
|
|
_emptyRE = re.compile(r"\s*(#.*)?$")
|
|
|
|
_fixedpointmappings = {8: "b", 16: "h", 32: "l"}
|
|
|
|
_formatcache = {}
|
|
|
|
|
|
def getformat(fmt, keep_pad_byte=False):
|
|
fmt = tostr(fmt, encoding="ascii")
|
|
try:
|
|
formatstring, names, fixes = _formatcache[fmt]
|
|
except KeyError:
|
|
lines = re.split("[\n;]", fmt)
|
|
formatstring = ""
|
|
names = []
|
|
fixes = {}
|
|
for line in lines:
|
|
if _emptyRE.match(line):
|
|
continue
|
|
m = _extraRE.match(line)
|
|
if m:
|
|
formatchar = m.group(1)
|
|
if formatchar != "x" and formatstring:
|
|
raise Error("a special fmt char must be first")
|
|
else:
|
|
m = _elementRE.match(line)
|
|
if not m:
|
|
raise Error("syntax error in fmt: '%s'" % line)
|
|
name = m.group(1)
|
|
formatchar = m.group(2)
|
|
if keep_pad_byte or formatchar != "x":
|
|
names.append(name)
|
|
if m.group(3):
|
|
# fixed point
|
|
before = int(m.group(3))
|
|
after = int(m.group(4))
|
|
bits = before + after
|
|
if bits not in [8, 16, 32]:
|
|
raise Error("fixed point must be 8, 16 or 32 bits long")
|
|
formatchar = _fixedpointmappings[bits]
|
|
assert m.group(5) == "F"
|
|
fixes[name] = after
|
|
formatstring = formatstring + formatchar
|
|
_formatcache[fmt] = formatstring, names, fixes
|
|
return formatstring, names, fixes
|
|
|
|
|
|
def _test():
|
|
fmt = """
|
|
# comments are allowed
|
|
> # big endian (see documentation for struct)
|
|
# empty lines are allowed:
|
|
|
|
ashort: h
|
|
along: l
|
|
abyte: b # a byte
|
|
achar: c
|
|
astr: 5s
|
|
afloat: f; adouble: d # multiple "statements" are allowed
|
|
afixed: 16.16F
|
|
abool: ?
|
|
apad: x
|
|
"""
|
|
|
|
print("size:", calcsize(fmt))
|
|
|
|
class foo(object):
|
|
pass
|
|
|
|
i = foo()
|
|
|
|
i.ashort = 0x7FFF
|
|
i.along = 0x7FFFFFFF
|
|
i.abyte = 0x7F
|
|
i.achar = "a"
|
|
i.astr = "12345"
|
|
i.afloat = 0.5
|
|
i.adouble = 0.5
|
|
i.afixed = 1.5
|
|
i.abool = True
|
|
|
|
data = pack(fmt, i)
|
|
print("data:", repr(data))
|
|
print(unpack(fmt, data))
|
|
i2 = foo()
|
|
unpack(fmt, data, i2)
|
|
print(vars(i2))
|
|
|
|
|
|
if __name__ == "__main__":
|
|
_test()
|