from typing import Optional
from .bits import Bits
from ..ast.base import _make_name
from .. import operations
from .bool import Bool
from .bv import BV, BVS, BVV
[docs]class String(Bits):
"""
Base class that represent the AST of a String object and implements all the operation useful to create and modify the AST.
Do not instantiate this class directly, instead use StringS or StringV to construct a symbol or value, and then use
operations to construct more complicated expressions.
"""
__slots__ = ("string_length",)
# Identifier used by composite solver in order to identify if a certain constraints contains
# variables of type string... In this case cvc4 would handle the solving part.
#
# TODO: Find a smarter way to do this!
STRING_TYPE_IDENTIFIER = "STRING_"
GENERATED_BVS_IDENTIFIER = "BVS_"
MAX_LENGTH = 10000
[docs] def __init__(self, *args, length: int, **kwargs):
"""
:param length: The string byte length
"""
super().__init__(*args, length=length, **kwargs)
self.string_length: int = length
def __getitem__(self, rng):
"""
This is a big endian indexer that takes its arguments as bits but returns bytes.
Returns the range of bits in self defined by: [rng.start, rng.end], indexed from the end
The bit range may not internally divide any bytes; i.e. low and (high+1) must both be divisible by 8
Examples:
self[7:0] -- returns the last byte of self
self[15:0] -- returns the last two bytes of self
self[8:0] -- Error! [8:0] is 9 bits, it asks for individual bits of the second to last byte!
self[8:1] -- Error! [8:1] asks for 1 bit from the second to last byte and 7 from the last byte!
"""
if type(rng) is slice:
bits_low = rng.start if rng.start is not None else 0
bits_high = rng.stop if rng.stop is not None else 8 * (self.string_length - 1)
if bits_high % 8 != 0 or (bits_low + 1) % 8 != 0:
raise ValueError("Bit indicies must not internally divide bytes!")
# high / low form a reverse-indexed byte index
high = bits_high // 8
low = bits_low // 8
if high < 0:
high = self.string_length + high
if low < 0:
low = self.string_length + low
# StrSubstr takes a front-indexed byte index as a starting point, and a length
start_idx = self.string_length - 1 - low
if high > low:
return StrSubstr(start_idx, 0, self)
return StrSubstr(start_idx, 1 + low - high, self)
else:
raise ValueError("Only slices allowed for string extraction")
@staticmethod
# TODO: Figure out what to convert here
#
# The use case that i found useful here is during the concretization
# of a symbolic address in memory.
# When angr has to do this it creates a claripy.If constraints in this form
# If(condition, <value_read_if_condition_true>, <value_read_if_condition_false>).
# In some case <value_read_if_condition_false> can be MEM_UNINITIALIZED expressed as BVV
#
# What should we return in this case?
def _from_BV(like, value): # pylint: disable=unused-argument
return value
@staticmethod
def _from_str(like, value): # pylint: disable=unused-argument
return StringV(value)
[docs] def strReplace(self, str_to_replace, replacement):
"""
Replace the first occurence of str_to_replace with replacement
:param claripy.ast.String str_to_replace: pattern that has to be replaced
:param claripy.ast.String replacement: replacement pattern
"""
return StrReplace(self, str_to_replace, replacement)
[docs] def toInt(self, bitlength):
"""
Convert the string to a bitvector holding the integer
representation of the string
:param bitlength: size of the biitvector holding the result
"""
return StrToInt(self, bitlength)
[docs] def indexOf(self, pattern, start_idx, bitlength):
"""
Return the start index of the pattern inside the input string in a
Bitvector representation, otherwise it returns -1 (always using a BitVector)
:param bitlength: size of the biitvector holding the result
"""
return StrIndexOf(self, pattern, start_idx, bitlength)
[docs] def raw_to_bv(self):
"""
A counterpart to FP.raw_to_bv - does nothing and returns itself.
"""
if self.symbolic:
return BVS(
next(iter(self.variables)).replace(self.STRING_TYPE_IDENTIFIER, self.GENERATED_BVS_IDENTIFIER),
self.length,
)
else:
return BVV(ord(self.args[0]), self.length)
[docs] def raw_to_fp(self):
return self.raw_to_bv().raw_to_fp()
[docs]def StringS(name, size, uninitialized=False, explicit_name=False, **kwargs):
"""
Create a new symbolic string (analogous to z3.String())
:param name: The name of the symbolic string (i. e. the name of the variable)
:param size: The size in bytes of the string (i. e. the length of the string)
:param uninitialized: Whether this value should be counted as an "uninitialized" value in the course of an
analysis.
:param bool explicit_name: If False, an identifier is appended to the name to ensure uniqueness.
:returns: The String object representing the symbolic string
"""
n = _make_name(String.STRING_TYPE_IDENTIFIER + name, size, False if explicit_name is None else explicit_name)
result = String(
"StringS",
(n, uninitialized),
length=8 * size,
symbolic=True,
eager_backends=None,
uninitialized=uninitialized,
variables={n},
**kwargs,
)
return result
[docs]def StringV(value, length: Optional[int] = None, **kwargs):
"""
Create a new Concrete string (analogous to z3.StringVal())
:param value: The constant value of the concrete string
:param length: The byte length of the string
:returns: The String object representing the concrete string
"""
if length is None:
length = len(value)
if length < len(value):
raise ValueError("Can't make a concrete string value longer than the specified length!")
result = String("StringV", (value, length), length=8 * length, **kwargs)
return result
StrConcat = operations.op("StrConcat", String, String, calc_length=operations.str_concat_length_calc, bound=False)
StrSubstr = operations.op("StrSubstr", (BV, BV, String), String, calc_length=operations.substr_length_calc, bound=False)
StrLen = operations.op("StrLen", (String, int), BV, calc_length=operations.strlen_bv_size_calc, bound=False)
StrReplace = operations.op(
"StrReplace",
(String, String, String),
String,
extra_check=operations.str_replace_check,
calc_length=operations.str_replace_length_calc,
bound=False,
)
StrContains = operations.op("StrContains", (String, String), Bool, bound=False)
StrPrefixOf = operations.op("StrPrefixOf", (String, String), Bool, bound=False)
StrSuffixOf = operations.op("StrSuffixOf", (String, String), Bool, bound=False)
StrIndexOf = operations.op(
"StrIndexOf", (String, String, BV, int), BV, calc_length=operations.strindexof_bv_size_calc, bound=False
)
StrToInt = operations.op("StrToInt", (String, int), BV, calc_length=operations.strtoint_bv_size_calc, bound=False)
IntToStr = operations.op("IntToStr", (BV,), String, calc_length=operations.int_to_str_length_calc, bound=False)
StrIsDigit = operations.op("StrIsDigit", (String,), Bool, bound=False)
# Equality / inequality check
String.__eq__ = operations.op("__eq__", (String, String), Bool)
String.__ne__ = operations.op("__ne__", (String, String), Bool)
# String manipulation
String.__add__ = StrConcat
String.StrSubstr = staticmethod(StrSubstr)
String.StrConcat = staticmethod(StrConcat)
String.StrLen = staticmethod(StrLen)
String.StrReplace = staticmethod(StrReplace)
String.StrContains = staticmethod(StrContains)
String.StrPrefixOf = staticmethod(StrPrefixOf)
String.StrSuffixOf = staticmethod(StrSuffixOf)
String.StrIndexOf = staticmethod(StrIndexOf)
String.StrToInt = staticmethod(StrToInt)
String.StrIsDigit = staticmethod(StrIsDigit)
String.IntToStr = staticmethod(IntToStr)