Crate cobs2

Encoding and decoding of COBS (Consistent Overhead Byte Stuffing)

Intro

This crate provides functions for encoding and decoding of COBS, and a minor variant of COBS known as COBS/R.

What Is COBS?

COBS is a method of encoding a packet of bytes into a form that contains no bytes with value zero (0x00). The input packet of bytes can contain bytes in the full range of 0x00 to 0xFF. The COBS encoded packet is guaranteed to generate packets with bytes only in the range 0x01 to 0xFF. Thus, in a communication protocol, packet boundaries can be reliably delimited with 0x00 bytes.

The COBS encoding does have to increase the packet size to achieve this encoding. However, compared to other byte-stuffing methods, the packet size increase is reasonable and predictable. COBS always adds 1 byte to the message length. Additionally, for longer packets of length n, it may add n/254 (rounded down) additional bytes to the encoded packet size.

For example, compare to the PPP protocol, which uses 0x7E bytes to delimit PPP packets. The PPP protocol uses an “escape” style of byte stuffing, replacing all occurences of 0x7E bytes in the packet with 0x7D 0x5E. But that byte-stuffing method can potentially double the size of the packet in the worst case. COBS uses a different method for byte-stuffing, which has a much more reasonable worst-case overhead.

For more details about COBS, see the references.

What is COBS/R?

I have included a variant on COBS, COBS/R, which slightly modifies COBS to often avoid the +1 byte overhead of COBS. So in many cases, especially for smaller packets, the size of a COBS/R encoded packet is the same size as the original packet. See the cobsr module for more details about COBS/R.

References

Consistent Overhead Byte Stuffing
Stuart Cheshire and Mary Baker
IEEE/ACM Transations on Networking, Vol. 7, No. 2, April 1999

Consistent Overhead Byte Stuffing (for IEEE)
http://www.stuartcheshire.org/papers/COBSforToN.pdf

PPP Consistent Overhead Byte Stuffing (COBS)
PPP Working Group Internet Draft
James Carlson, IronBridge Networks
Stuart Cheshire and Mary Baker, Stanford University
November 1997

PPP Consistent Overhead Byte Stuffing (COBS)
http://tools.ietf.org/html/draft-ietf-pppext-cobs-00

License

The code is released under the MIT license. See LICENSE.txt for details.

Modules

cobs

This module contains functions for standard COBS encoding and decoding.

cobsr

Consistent Overhead Byte Stuffing—Reduced (COBS/R)

Enums

Error

Errors that can occur during COBS encoding/decoding.

Type Aliases

Result

The return type for encoding and decoding functions, based on core::result::Result, in which the error type is Error.