182 lines
4.3 KiB
Python
182 lines
4.3 KiB
Python
"""Various I/O and serialization utilities."""
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import binascii
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import contextlib
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import io
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import struct
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import time
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def send(conn, data):
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"""Send data blob to connection socket."""
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conn.sendall(data)
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def recv(conn, size):
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"""
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Receive bytes from connection socket or stream.
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If size is struct.calcsize()-compatible format, use it to unpack the data.
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Otherwise, return the plain blob as bytes.
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"""
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try:
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fmt = size
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size = struct.calcsize(fmt)
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except TypeError:
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fmt = None
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try:
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_read = conn.recv
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except AttributeError:
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_read = conn.read
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res = io.BytesIO()
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while size > 0:
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buf = _read(size)
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if not buf:
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raise EOFError
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size = size - len(buf)
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res.write(buf)
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res = res.getvalue()
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if fmt:
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return struct.unpack(fmt, res)
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else:
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return res
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def read_frame(conn):
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"""Read size-prefixed frame from connection."""
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size, = recv(conn, '>L')
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return recv(conn, size)
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def bytes2num(s):
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"""Convert MSB-first bytes to an unsigned integer."""
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res = 0
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for i, c in enumerate(reversed(bytearray(s))):
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res += c << (i * 8)
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return res
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def num2bytes(value, size):
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"""Convert an unsigned integer to MSB-first bytes with specified size."""
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res = []
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for _ in range(size):
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res.append(value & 0xFF)
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value = value >> 8
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assert value == 0
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return bytes(bytearray(list(reversed(res))))
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def pack(fmt, *args):
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"""Serialize MSB-first message."""
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return struct.pack('>' + fmt, *args)
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def frame(*msgs):
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"""Serialize MSB-first length-prefixed frame."""
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res = io.BytesIO()
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for msg in msgs:
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res.write(msg)
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msg = res.getvalue()
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return pack('L', len(msg)) + msg
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def crc24(blob):
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"""See https://tools.ietf.org/html/rfc4880#section-6.1 for details."""
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CRC24_INIT = 0x0B704CE
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CRC24_POLY = 0x1864CFB
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crc = CRC24_INIT
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for octet in bytearray(blob):
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crc ^= (octet << 16)
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for _ in range(8):
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crc <<= 1
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if crc & 0x1000000:
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crc ^= CRC24_POLY
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assert 0 <= crc < 0x1000000
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crc_bytes = struct.pack('>L', crc)
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assert crc_bytes[:1] == b'\x00'
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return crc_bytes[1:]
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def bit(value, i):
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"""Extract the i-th bit out of value."""
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return 1 if value & (1 << i) else 0
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def low_bits(value, n):
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"""Extract the lowest n bits out of value."""
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return value & ((1 << n) - 1)
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def split_bits(value, *bits):
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"""
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Split integer value into list of ints, according to `bits` list.
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For example, split_bits(0x1234, 4, 8, 4) == [0x1, 0x23, 0x4]
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"""
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result = []
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for b in reversed(bits):
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mask = (1 << b) - 1
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result.append(value & mask)
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value = value >> b
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assert value == 0
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result.reverse()
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return result
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def readfmt(stream, fmt):
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"""Read and unpack an object from stream, using a struct format string."""
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size = struct.calcsize(fmt)
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blob = stream.read(size)
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return struct.unpack(fmt, blob)
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def prefix_len(fmt, blob):
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"""Prefix `blob` with its size, serialized using `fmt` format."""
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return struct.pack(fmt, len(blob)) + blob
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def time_format(t):
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"""Utility for consistent time formatting."""
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return time.strftime('%Y-%m-%d %H:%M:%S', time.localtime(t))
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def hexlify(blob):
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"""Utility for consistent hexadecimal formatting."""
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return binascii.hexlify(blob).decode('ascii').upper()
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class Reader(object):
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"""Read basic type objects out of given stream."""
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def __init__(self, stream):
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"""Create a non-capturing reader."""
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self.s = stream
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self._captured = None
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def readfmt(self, fmt):
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"""Read a specified object, using a struct format string."""
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size = struct.calcsize(fmt)
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blob = self.read(size)
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obj, = struct.unpack(fmt, blob)
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return obj
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def read(self, size=None):
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"""Read `size` bytes from stream."""
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blob = self.s.read(size)
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if size is not None and len(blob) < size:
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raise EOFError
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if self._captured:
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self._captured.write(blob)
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return blob
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@contextlib.contextmanager
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def capture(self, stream):
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"""Capture all data read during this context."""
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self._captured = stream
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try:
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yield
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finally:
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self._captured = None
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