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"""
Wrappers for doing binary IO on file-like objects
"""
import struct
import sys
import numpy
def bytesify(s):
if isinstance(s, bytes):
return s
else:
return s.encode()
# Standard size:
# short is 8 bits
# int and long are 32 bits
# long long is 64 bits
class BadMagicNumber(IOError):
pass
class BinaryFileReader:
"""
Wrapper for doing binary reads on any file like object.
Currently this is not heavily optimized (it uses the `struct` module to
unpack)
"""
def __init__(self, file, magic=None, is_little_endian=False):
self.is_little_endian = is_little_endian
self.file = file
if magic is not None:
# Attempt to read magic number and chuck endianess
bytes = file.read(4)
if struct.unpack(">I", bytes)[0] == magic:
pass
elif struct.unpack("<I", bytes)[0] == magic:
self.is_little_endian = True
else:
raise BadMagicNumber(
"File does not have expected magic number: {:x} != {:x} or {:x}".format(
magic, struct.unpack(">I", bytes)[0], struct.unpack("<I", bytes)[0]
)
)
# Set endian code
if self.is_little_endian:
self.endian_code = "<"
self.byteswap_needed = sys.byteorder != "little"
else:
self.endian_code = ">"
self.byteswap_needed = sys.byteorder != "big"
def unpack(self, format, buffer, byte_count=None):
pattern = f"{self.endian_code}{format}"
if byte_count is None:
byte_count = struct.calcsize(pattern)
return struct.unpack(pattern, buffer)
def read_and_unpack(self, format, byte_count=None):
"""
Read enough bytes to unpack according to `format` and return the
tuple of unpacked values.
"""
pattern = f"{self.endian_code}{format}"
if byte_count is None:
byte_count = struct.calcsize(pattern)
return struct.unpack(pattern, self.file.read(byte_count))
def read_c_string(self):
"""
Read a zero terminated (C style) string
"""
rval = []
while True:
ch = self.file.read(1)
assert len(ch) == 1, "Unexpected end of file"
if ch == b"\0":
break
rval.append(ch)
return b"".join(rval)
def read_raw_array(self, dtype, size):
a = numpy.fromfile(self.file, dtype=dtype, count=size)
if self.byteswap_needed:
a.byteswap()
return a
def read(self, byte_count=1):
return self.file.read(byte_count)
def tell(self):
return self.file.tell()
def skip(self, count):
self.file.seek(count, 1)
def seek(self, pos, whence=0):
return self.file.seek(pos, whence)
def read_uint8(self):
return self.read_and_unpack("B", 1)[0]
def read_uint16(self):
return self.read_and_unpack("H", 2)[0]
def read_uint32(self):
return self.read_and_unpack("L", 4)[0]
def read_uint64(self):
return self.read_and_unpack("Q", 8)[0]
def read_float(self):
return self.read_and_unpack("f", 4)[0]
class BinaryFileWriter:
"""
Wrapper for doing binary writes on any file like object.
Currently this is not heavily optimized (it uses the `struct` module to
unpack)
"""
def __init__(self, file, magic=None, is_little_endian=False):
self.is_little_endian = is_little_endian
if self.is_little_endian:
self.endian_code = "<"
else:
self.endian_code = ">"
self.file = file
if magic is not None:
self.write_uint32(magic)
def pack(self, format, buffer):
pattern = f"{self.endian_code}{format}"
return struct.pack(pattern, buffer)
def pack_and_write(self, format, value):
"""
Read enough bytes to unpack according to `format` and return the
tuple of unpacked values.
"""
pattern = f"{self.endian_code}{format}"
return self.file.write(struct.pack(pattern, value))
def write_c_string(self, value):
"""
Read a zero terminated (C style) string
"""
self.file.write(value)
self.file.write(b"\0")
def write_raw_array(self, value):
value.tofile(self.file)
def write(self, value):
return self.file.write(bytesify(value))
def skip(self, count):
self.file.seek(count, 1)
def tell(self):
return self.file.tell()
def seek(self, pos, whence=0):
return self.file.seek(pos, whence)
def write_uint8(self, value):
return self.pack_and_write("B", value)
def write_uint16(self, value):
return self.pack_and_write("H", value)
def write_uint32(self, value):
return self.pack_and_write("L", value)
def write_uint64(self, value):
return self.pack_and_write("Q", value)
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