bf5433b7c5
by converting them in the Python helper code into a positive value whose bit pattern is the 2's complement representation of the negative value.
129 lines
4.2 KiB
Python
129 lines
4.2 KiB
Python
# Copyright 2017-present Open Networking Foundation
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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#
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import math
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import re
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import socket
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'''
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This package contains several helper functions for encoding to and decoding from byte strings:
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- integers
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- IPv4 address strings
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- Ethernet address strings
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'''
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mac_pattern = re.compile('^([\da-fA-F]{2}:){5}([\da-fA-F]{2})$')
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def matchesMac(mac_addr_string):
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return mac_pattern.match(mac_addr_string) is not None
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def encodeMac(mac_addr_string):
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return bytes.fromhex(mac_addr_string.replace(':', ''))
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def decodeMac(encoded_mac_addr):
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return ':'.join(s.hex() for s in encoded_mac_addr)
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ip_pattern = re.compile('^(\d{1,3}\.){3}(\d{1,3})$')
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def matchesIPv4(ip_addr_string):
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return ip_pattern.match(ip_addr_string) is not None
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def encodeIPv4(ip_addr_string):
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return socket.inet_aton(ip_addr_string)
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def decodeIPv4(encoded_ip_addr):
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return socket.inet_ntoa(encoded_ip_addr)
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def bitwidthToBytes(bitwidth):
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return int(math.ceil(bitwidth / 8.0))
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def encodeNum(number, bitwidth):
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byte_len = bitwidthToBytes(bitwidth)
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# If number is negative, calculate the positive number that its
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# 2's complement encoding would look like in 'bitwidth' bits.
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orig_number = number
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if number < 0:
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if number < -(2 ** (bitwidth-1)):
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raise Exception("Negative number, %d, has 2's complement representation that does not fit in %d bits" % (number, bitwidth))
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number = (2 ** bitwidth) + number
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num_str = '%x' % number
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if orig_number < 0:
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print("CONVERT_NEGATIVE_NUMBER debug: orig_number=%s number=%s bitwidth=%d num_str='%s'"
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"" % (orig_number, number, bitwidth, num_str))
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if number >= 2 ** bitwidth:
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raise Exception("Number, %d, does not fit in %d bits" % (number, bitwidth))
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return bytes.fromhex('0' * (byte_len * 2 - len(num_str)) + num_str)
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def decodeNum(encoded_number):
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return int(encoded_number.hex(), 16)
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def encode(x, bitwidth):
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'Tries to infer the type of `x` and encode it'
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byte_len = bitwidthToBytes(bitwidth)
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if (type(x) == list or type(x) == tuple) and len(x) == 1:
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x = x[0]
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encoded_bytes = None
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if type(x) == str:
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if matchesMac(x):
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encoded_bytes = encodeMac(x)
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elif matchesIPv4(x):
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encoded_bytes = encodeIPv4(x)
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else:
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# Assume that the string is already encoded
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encoded_bytes = x
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elif type(x) == int:
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encoded_bytes = encodeNum(x, bitwidth)
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else:
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raise Exception("Encoding objects of %r is not supported" % type(x))
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assert(len(encoded_bytes) == byte_len)
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return encoded_bytes
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if __name__ == '__main__':
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# TODO These tests should be moved out of main eventually
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mac = "aa:bb:cc:dd:ee:ff"
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enc_mac = encodeMac(mac)
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assert(enc_mac == '\xaa\xbb\xcc\xdd\xee\xff')
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dec_mac = decodeMac(enc_mac)
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assert(mac == dec_mac)
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ip = "10.0.0.1"
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enc_ip = encodeIPv4(ip)
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assert(enc_ip == '\x0a\x00\x00\x01')
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dec_ip = decodeIPv4(enc_ip)
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assert(ip == dec_ip)
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num = 1337
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byte_len = 5
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enc_num = encodeNum(num, byte_len * 8)
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assert(enc_num == '\x00\x00\x00\x05\x39')
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dec_num = decodeNum(enc_num)
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assert(num == dec_num)
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assert(matchesIPv4('10.0.0.1'))
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assert(not matchesIPv4('10.0.0.1.5'))
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assert(not matchesIPv4('1000.0.0.1'))
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assert(not matchesIPv4('10001'))
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assert(encode(mac, 6 * 8) == enc_mac)
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assert(encode(ip, 4 * 8) == enc_ip)
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assert(encode(num, 5 * 8) == enc_num)
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assert(encode((num,), 5 * 8) == enc_num)
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assert(encode([num], 5 * 8) == enc_num)
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num = 256
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byte_len = 2
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try:
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enc_num = encodeNum(num, 8)
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raise Exception("expected exception")
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except Exception as e:
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print(e)
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