cobs.cobs—COBS Encoding and Decoding

This module provides functions for encoding and decoding byte strings using the COBS encoding method.

In Python 2.x, the input type to the functions must be a byte string. Unicode strings may appear to work at first, but only if they can be automatically encoded to bytes using the ascii encoding. So Unicode strings should not be used.

In Python 3.x, byte strings are acceptable input. Types that implement the buffer protocol, providing a simple buffer of bytes, are also acceptable. Thus types such as bytearray and array('B',...) are accepted input. The output type is always a byte string.

encode() – COBS encode

The function encodes a byte string according to the COBS encoding method.

Parameter:data (byte string) – Data to encode.
Returns:COBS encoded data.
Return type:byte string

The COBS encoded data is guaranteed not to contain zero b'\x00' bytes.

The encoded data length will always be at least one byte longer than the input length. Additionally, it may increase by one extra byte for every 254 bytes of input data.

decode() – COBS decode

The function decodes a byte string according to the COBS method.

Parameter:data (byte string) – COBS encoded data to decode.
Returns:Decoded data.
Return type:byte string

If a zero b'\x00' byte is found in the encoded input data, a cobs.cobs.DecodeError exception will be raised.

If the final length code byte in the encoded input data is not followed by the expected number of data bytes, this is an invalid COBS encoded data input, and cobs.cobs.DecodeError is raised.


Basic usage example, in Python 2.x using byte string inputs:

>>> from cobs import cobs

>>> encoded = cobs.encode(b'Hello world\x00This is a test')
>>> encoded
'\x0cHello world\x0fThis is a test'

>>> cobs.decode(encoded)
'Hello world\x00This is a test'

For Python 3.x, input cannot be Unicode strings. Byte strings are acceptable input. Also, any type that implements the buffer protocol, providing a single block of bytes, is also acceptable as input:

>>> from cobs import cobs
>>> encoded = cobs.encode(bytearray(b'Hello world\x00This is a test'))
>>> encoded
b'\x0cHello world\x0fThis is a test'
>>> cobs.decode(encoded)
b'Hello world\x00This is a test'

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