/usr/lib/python3/dist-packages/construct/macros.py is in python3-construct 2.5.2-0.1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 | import six
from construct.lib.py3compat import int2byte
from construct.lib import (BitStreamReader, BitStreamWriter, encode_bin, decode_bin)
from construct.core import (Struct, MetaField, StaticField, FormatField,
OnDemand, Pointer, Switch, Value, RepeatUntil, MetaArray, Sequence, Range,
Select, Pass, SizeofError, Buffered, Restream, Reconfig)
from construct.adapters import (BitIntegerAdapter, PaddingAdapter,
ConstAdapter, CStringAdapter, LengthValueAdapter, IndexingAdapter,
PaddedStringAdapter, FlagsAdapter, StringAdapter, MappingAdapter)
try:
from sys import maxsize
except ImportError:
from sys import maxint as maxsize
#===============================================================================
# fields
#===============================================================================
def Field(name, length):
"""
A field consisting of a specified number of bytes.
:param name: the name of the field
:param length: the length of the field. the length can be either an integer
(StaticField), or a function that takes the context as an argument and
returns the length (MetaField)
"""
if callable(length):
return MetaField(name, length)
else:
return StaticField(name, length)
def BitField(name, length, swapped = False, signed = False, bytesize = 8):
r"""
BitFields, as the name suggests, are fields that operate on raw, unaligned
bits, and therefore must be enclosed in a BitStruct. Using them is very
similar to all normal fields: they take a name and a length (in bits).
:param name: name of the field
:param length: number of bits in the field, or a function that takes
the context as its argument and returns the length
:param swapped: whether the value is byte-swapped
:param signed: whether the value is signed
:param bytesize: number of bits per byte, for byte-swapping
Example::
>>> foo = BitStruct("foo",
... BitField("a", 3),
... Flag("b"),
... Padding(3),
... Nibble("c"),
... BitField("d", 5),
... )
>>> foo.parse("\xe1\x1f")
Container(a = 7, b = False, c = 8, d = 31)
>>> foo = BitStruct("foo",
... BitField("a", 3),
... Flag("b"),
... Padding(3),
... Nibble("c"),
... Struct("bar",
... Nibble("d"),
... Bit("e"),
... )
... )
>>> foo.parse("\xe1\x1f")
Container(a = 7, b = False, bar = Container(d = 15, e = 1), c = 8)
"""
return BitIntegerAdapter(Field(name, length),
length,
swapped=swapped,
signed=signed,
bytesize=bytesize
)
def Padding(length, pattern = six.b("\x00"), strict = False):
r"""A padding field (value is discarded)
:param length: the length of the field. the length can be either an integer,
or a function that takes the context as an argument and returns the length
:param pattern: the padding pattern (character) to use. default is "\x00"
:param strict: whether or not to raise an exception is the actual padding
pattern mismatches the desired pattern. default is False.
"""
return PaddingAdapter(Field(None, length),
pattern = pattern,
strict = strict,
)
def Flag(name, truth = 1, falsehood = 0, default = False):
"""
A flag.
Flags are usually used to signify a Boolean value, and this construct
maps values onto the ``bool`` type.
.. note:: This construct works with both bit and byte contexts.
.. warning:: Flags default to False, not True. This is different from the
C and Python way of thinking about truth, and may be subject to change
in the future.
:param name: field name
:param truth: value of truth (default 1)
:param falsehood: value of falsehood (default 0)
:param default: default value (default False)
"""
return SymmetricMapping(Field(name, 1),
{True : int2byte(truth), False : int2byte(falsehood)},
default = default,
)
#===============================================================================
# field shortcuts
#===============================================================================
def Bit(name):
"""A 1-bit BitField; must be enclosed in a BitStruct"""
return BitField(name, 1)
def Nibble(name):
"""A 4-bit BitField; must be enclosed in a BitStruct"""
return BitField(name, 4)
def Octet(name):
"""An 8-bit BitField; must be enclosed in a BitStruct"""
return BitField(name, 8)
def UBInt8(name):
"""Unsigned, big endian 8-bit integer"""
return FormatField(name, ">", "B")
def UBInt16(name):
"""Unsigned, big endian 16-bit integer"""
return FormatField(name, ">", "H")
def UBInt32(name):
"""Unsigned, big endian 32-bit integer"""
return FormatField(name, ">", "L")
def UBInt64(name):
"""Unsigned, big endian 64-bit integer"""
return FormatField(name, ">", "Q")
def SBInt8(name):
"""Signed, big endian 8-bit integer"""
return FormatField(name, ">", "b")
def SBInt16(name):
"""Signed, big endian 16-bit integer"""
return FormatField(name, ">", "h")
def SBInt32(name):
"""Signed, big endian 32-bit integer"""
return FormatField(name, ">", "l")
def SBInt64(name):
"""Signed, big endian 64-bit integer"""
return FormatField(name, ">", "q")
def ULInt8(name):
"""Unsigned, little endian 8-bit integer"""
return FormatField(name, "<", "B")
def ULInt16(name):
"""Unsigned, little endian 16-bit integer"""
return FormatField(name, "<", "H")
def ULInt32(name):
"""Unsigned, little endian 32-bit integer"""
return FormatField(name, "<", "L")
def ULInt64(name):
"""Unsigned, little endian 64-bit integer"""
return FormatField(name, "<", "Q")
def SLInt8(name):
"""Signed, little endian 8-bit integer"""
return FormatField(name, "<", "b")
def SLInt16(name):
"""Signed, little endian 16-bit integer"""
return FormatField(name, "<", "h")
def SLInt32(name):
"""Signed, little endian 32-bit integer"""
return FormatField(name, "<", "l")
def SLInt64(name):
"""Signed, little endian 64-bit integer"""
return FormatField(name, "<", "q")
def UNInt8(name):
"""Unsigned, native endianity 8-bit integer"""
return FormatField(name, "=", "B")
def UNInt16(name):
"""Unsigned, native endianity 16-bit integer"""
return FormatField(name, "=", "H")
def UNInt32(name):
"""Unsigned, native endianity 32-bit integer"""
return FormatField(name, "=", "L")
def UNInt64(name):
"""Unsigned, native endianity 64-bit integer"""
return FormatField(name, "=", "Q")
def SNInt8(name):
"""Signed, native endianity 8-bit integer"""
return FormatField(name, "=", "b")
def SNInt16(name):
"""Signed, native endianity 16-bit integer"""
return FormatField(name, "=", "h")
def SNInt32(name):
"""Signed, native endianity 32-bit integer"""
return FormatField(name, "=", "l")
def SNInt64(name):
"""Signed, native endianity 64-bit integer"""
return FormatField(name, "=", "q")
def BFloat32(name):
"""Big endian, 32-bit IEEE floating point number"""
return FormatField(name, ">", "f")
def LFloat32(name):
"""Little endian, 32-bit IEEE floating point number"""
return FormatField(name, "<", "f")
def NFloat32(name):
"""Native endianity, 32-bit IEEE floating point number"""
return FormatField(name, "=", "f")
def BFloat64(name):
"""Big endian, 64-bit IEEE floating point number"""
return FormatField(name, ">", "d")
def LFloat64(name):
"""Little endian, 64-bit IEEE floating point number"""
return FormatField(name, "<", "d")
def NFloat64(name):
"""Native endianity, 64-bit IEEE floating point number"""
return FormatField(name, "=", "d")
#===============================================================================
# arrays
#===============================================================================
def Array(count, subcon):
r"""
Repeats the given unit a fixed number of times.
:param count: number of times to repeat
:param subcon: construct to repeat
Example::
>>> c = Array(4, UBInt8("foo"))
>>> c.parse("\x01\x02\x03\x04")
[1, 2, 3, 4]
>>> c.parse("\x01\x02\x03\x04\x05\x06")
[1, 2, 3, 4]
>>> c.build([5,6,7,8])
'\x05\x06\x07\x08'
>>> c.build([5,6,7,8,9])
Traceback (most recent call last):
...
construct.core.RangeError: expected 4..4, found 5
"""
if callable(count):
con = MetaArray(count, subcon)
else:
con = MetaArray(lambda ctx: count, subcon)
con._clear_flag(con.FLAG_DYNAMIC)
return con
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 OpenRange(mincount, subcon):
return Range(mincount, maxsize, subcon)
def GreedyRange(subcon):
r"""
Repeats the given unit one or more times.
:param subcon: construct to repeat
Example::
>>> from construct import GreedyRange, UBInt8
>>> c = GreedyRange(UBInt8("foo"))
>>> c.parse("\x01")
[1]
>>> c.parse("\x01\x02\x03")
[1, 2, 3]
>>> c.parse("\x01\x02\x03\x04\x05\x06")
[1, 2, 3, 4, 5, 6]
>>> c.parse("")
Traceback (most recent call last):
...
construct.core.RangeError: expected 1..2147483647, found 0
>>> c.build([1,2])
'\x01\x02'
>>> c.build([])
Traceback (most recent call last):
...
construct.core.RangeError: expected 1..2147483647, found 0
"""
return OpenRange(1, subcon)
def OptionalGreedyRange(subcon):
r"""
Repeats the given unit zero or more times. This repeater can't
fail, as it accepts lists of any length.
:param subcon: construct to repeat
Example::
>>> from construct import OptionalGreedyRange, UBInt8
>>> c = OptionalGreedyRange(UBInt8("foo"))
>>> c.parse("")
[]
>>> c.parse("\x01\x02")
[1, 2]
>>> c.build([])
''
>>> c.build([1,2])
'\x01\x02'
"""
return OpenRange(0, subcon)
#===============================================================================
# subconstructs
#===============================================================================
def Optional(subcon):
"""An optional construct. if parsing fails, returns None.
:param subcon: the subcon to optionally parse or build
"""
return Select(subcon.name, subcon, Pass)
def Bitwise(subcon):
"""Converts the stream to bits, and passes the bitstream to subcon
:param subcon: a bitwise construct (usually BitField)
"""
# subcons larger than MAX_BUFFER will be wrapped by Restream instead
# of Buffered. implementation details, don't stick your nose in :)
MAX_BUFFER = 1024 * 8
def resizer(length):
if length & 7:
raise SizeofError("size must be a multiple of 8", length)
return length >> 3
if not subcon._is_flag(subcon.FLAG_DYNAMIC) and subcon.sizeof() < MAX_BUFFER:
con = Buffered(subcon,
encoder = decode_bin,
decoder = encode_bin,
resizer = resizer
)
else:
con = Restream(subcon,
stream_reader = BitStreamReader,
stream_writer = BitStreamWriter,
resizer = resizer)
return con
def Aligned(subcon, modulus = 4, pattern = six.b("\x00")):
r"""Aligns subcon to modulus boundary using padding pattern
:param subcon: the subcon to align
:param modulus: the modulus boundary (default is 4)
:param pattern: the padding pattern (default is \x00)
"""
if modulus < 2:
raise ValueError("modulus must be >= 2", modulus)
def padlength(ctx):
return (modulus - (subcon._sizeof(ctx) % modulus)) % modulus
return SeqOfOne(subcon.name,
subcon,
# ??????
# ??????
# ??????
# ??????
Padding(padlength, pattern = pattern),
nested = False,
)
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 Embedded(subcon):
"""Embeds a struct into the enclosing struct.
:param subcon: the struct to embed
"""
return Reconfig(subcon.name, subcon, subcon.FLAG_EMBED)
def Rename(newname, subcon):
"""Renames an existing construct
:param newname: the new name
:param subcon: the subcon to rename
"""
return Reconfig(newname, subcon)
def Alias(newname, oldname):
"""Creates an alias for an existing element in a struct
:param newname: the new name
:param oldname: the name of an existing element
"""
return Value(newname, lambda ctx: ctx[oldname])
#===============================================================================
# mapping
#===============================================================================
def SymmetricMapping(subcon, mapping, default = NotImplemented):
"""Defines a symmetrical mapping: a->b, b->a.
:param subcon: the subcon to map
:param mapping: the encoding mapping (a dict); the decoding mapping is
achieved by reversing this mapping
:param default: the default value to use when no mapping is found. if no
default value is given, and exception is raised. setting to Pass would
return the value "as is" (unmapped)
"""
reversed_mapping = dict((v, k) for k, v in mapping.items())
return MappingAdapter(subcon,
encoding = mapping,
decoding = reversed_mapping,
encdefault = default,
decdefault = default,
)
def Enum(subcon, **kw):
r"""A set of named values mapping.
:param subcon: the subcon to map
:param \*\*kw: keyword arguments which serve as the encoding mapping
:param _default_: an optional, keyword-only argument that specifies the
default value to use when the mapping is undefined. if not given,
and exception is raised when the mapping is undefined. use `Pass` to
pass the unmapped value as-is
"""
return SymmetricMapping(subcon, kw, kw.pop("_default_", NotImplemented))
def FlagsEnum(subcon, **kw):
r"""A set of flag values mapping.
:param subcon: the subcon to map
:param \*\*kw: keyword arguments which serve as the encoding mapping
"""
return FlagsAdapter(subcon, kw)
#===============================================================================
# structs
#===============================================================================
def AlignedStruct(name, *subcons, **kw):
r"""A struct of aligned fields
:param name: the name of the struct
:param \*subcons: the subcons that make up this structure
:param \*\*kw: keyword arguments to pass to Aligned: 'modulus' and 'pattern'
"""
return Struct(name, *(Aligned(sc, **kw) for sc in subcons))
def BitStruct(name, *subcons):
r"""A struct of bitwise fields
:param name: the name of the struct
:param \*subcons: the subcons that make up this structure
"""
return Bitwise(Struct(name, *subcons))
def EmbeddedBitStruct(*subcons):
r"""An embedded BitStruct. no name is necessary.
:param \*subcons: the subcons that make up this structure
"""
return Bitwise(Embedded(Struct(None, *subcons)))
#===============================================================================
# strings
#===============================================================================
def String(name, length, encoding=None, padchar=None, paddir="right",
trimdir="right"):
r"""
A configurable, fixed-length string field.
The padding character must be specified for padding and trimming to work.
:param name: name
:param length: length, in bytes
:param encoding: encoding (e.g. "utf8") or None for no encoding
:param padchar: optional character to pad out strings
:param paddir: direction to pad out strings; one of "right", "left", or "both"
:param str trim: direction to trim strings; one of "right", "left"
Example::
>>> from construct import String
>>> String("foo", 5).parse("hello")
'hello'
>>>
>>> String("foo", 12, encoding = "utf8").parse("hello joh\xd4\x83n")
u'hello joh\u0503n'
>>>
>>> foo = String("foo", 10, padchar = "X", paddir = "right")
>>> foo.parse("helloXXXXX")
'hello'
>>> foo.build("hello")
'helloXXXXX'
"""
con = StringAdapter(Field(name, length), encoding=encoding)
if padchar is not None:
con = PaddedStringAdapter(con, padchar=padchar, paddir=paddir,
trimdir=trimdir)
return con
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,
)
def CString(name, terminators=six.b("\x00"), encoding=None,
char_field=Field(None, 1)):
r"""
A string ending in a terminator.
``CString`` is similar to the strings of C, C++, and other related
programming languages.
By default, the terminator is the NULL byte (b``0x00``).
:param name: name
:param terminators: sequence of valid terminators, in order of preference
:param encoding: encoding (e.g. "utf8") or None for no encoding
:param char_field: construct representing a single character
Example::
>>> foo = CString("foo")
>>> foo.parse(b"hello\x00")
b'hello'
>>> foo.build(b"hello")
b'hello\x00'
>>> foo = CString("foo", terminators = b"XYZ")
>>> foo.parse(b"helloX")
b'hello'
>>> foo.parse(b"helloY")
b'hello'
>>> foo.parse(b"helloZ")
b'hello'
>>> foo.build(b"hello")
b'helloX'
"""
return Rename(name,
CStringAdapter(
RepeatUntil(lambda obj, ctx: obj in terminators, char_field),
terminators=terminators,
encoding=encoding,
)
)
#===============================================================================
# conditional
#===============================================================================
def IfThenElse(name, predicate, then_subcon, else_subcon):
"""An if-then-else conditional construct: if the predicate indicates True,
`then_subcon` will be used; otherwise `else_subcon`
:param name: the name of the construct
:param predicate: a function taking the context as an argument and returning True or False
:param then_subcon: the subcon that will be used if the predicate returns True
:param else_subcon: the subcon that will be used if the predicate returns False
"""
return Switch(name, lambda ctx: bool(predicate(ctx)),
{
True : then_subcon,
False : else_subcon,
}
)
def If(predicate, subcon, elsevalue = None):
"""An if-then conditional construct: if the predicate indicates True,
subcon will be used; otherwise, `elsevalue` will be returned instead.
:param predicate: a function taking the context as an argument and returning True or False
:param subcon: the subcon that will be used if the predicate returns True
:param elsevalue: the value that will be used should the predicate return False.
by default this value is None.
"""
return IfThenElse(subcon.name,
predicate,
subcon,
Value("elsevalue", lambda ctx: elsevalue)
)
#===============================================================================
# misc
#===============================================================================
def OnDemandPointer(offsetfunc, subcon, force_build = True):
"""An on-demand pointer.
:param offsetfunc: a function taking the context as an argument and returning
the absolute stream position
:param subcon: the subcon that will be parsed from the `offsetfunc()` stream position on demand
:param force_build: see OnDemand. by default True.
"""
return OnDemand(Pointer(offsetfunc, subcon),
advance_stream = False,
force_build = force_build
)
def Magic(data):
"""A 'magic number' construct. it is used for file signatures, etc., to validate
that the given pattern exists.
Example::
elf_header = Struct("elf_header",
Magic("\x7fELF"),
# ...
)
"""
return ConstAdapter(Field(None, len(data)), data)
|