97 lines
2.8 KiB
Python
97 lines
2.8 KiB
Python
import struct
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class ByteReader:
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"""
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The ByteReader object is used when decoding various variable sized structures.
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all functions raise EOFError when attempting to read beyond the end of the buffer.
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functions starting with `read` advance the current position.
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"""
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def __init__(self, data):
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self.data = data
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self.o = 0
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def readbyte(self):
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"""
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Reads a single byte
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"""
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if self.o + 1 > len(self.data):
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raise EOFError()
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self.o += 1
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return struct.unpack_from("<B", self.data, self.o - 1)[0]
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def testbyte(self, bytevalue):
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"""
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returns True when the current bytes matches `bytevalue`.
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"""
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if self.o + 1 > len(self.data):
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raise EOFError()
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return self.data[self.o] == bytevalue
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def readword(self):
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"""
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Reads a 16 bit unsigned little endian value
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"""
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if self.o + 2 > len(self.data):
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raise EOFError()
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self.o += 2
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return struct.unpack_from("<H", self.data, self.o - 2)[0]
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def readdword(self):
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"""
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Reads a 32 bit unsigned little endian value
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"""
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if self.o + 4 > len(self.data):
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raise EOFError()
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self.o += 4
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return struct.unpack_from("<L", self.data, self.o - 4)[0]
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def readbytes(self, n=None):
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"""
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Reads the specified number of bytes, or
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when no size was specified, the remaining bytes in the buffer
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"""
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if n is None:
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n = len(self.data) - self.o
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if self.o + n > len(self.data):
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raise EOFError()
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self.o += n
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return self.data[self.o-n:self.o]
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def readlongstring(self):
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"""
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Reads a cp1251 encoded string prefixed with a dword sized length
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"""
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namelen = self.readdword()
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return self.readbytes(namelen).decode("cp1251")
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def readname(self):
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"""
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Reads a cp1251 encoded string prefixed with a byte sized length
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"""
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namelen = self.readbyte()
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return self.readbytes(namelen).decode("cp1251")
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def readtoseperator(self, sep):
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"""
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reads bytes upto a bytes sequence matching `sep`.
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when no `sep` is found, return the remaining bytes in the buffer.
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"""
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if self.o > len(self.data):
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raise EOFError()
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oldoff = self.o
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off = self.data.find(sep, self.o)
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if off >= 0:
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self.o = off + len(sep)
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return self.data[oldoff:off]
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else:
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self.o = len(self.data)
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return self.data[oldoff:]
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def eof(self):
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"""
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return True when the current position is at or beyond the end of the buffer.
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"""
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return self.o >= len(self.data)
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