Consistent Overhead Byte Stuffing

Sequential byte stuffing is an algorithm for encoding data bytes, which leads to efficient, reliable unambiguous packet framing regardless of packet content, making it easy for applications to recover from malformed packets. It uses a specific byte value, typically zero, as the batch separator. When zero is used as a delimiter, the algorithm replaces each zero data byte with a non-zero value, so that no zero bytes of data will appear in the package and, therefore, to be construed as the boundaries of packages.
Byte stuffing is a process that converts a sequence of data bytes that may contain illegal or reserved values, such as a packet delimiter in a potentially longer sequence that contains no occurrences of those values. The extra length of the transformed sequence are usually called the cost of the algorithm. The cobs algorithm tightly bounds in the worst case overhead, limiting it to at least one byte and a maximum of ⌈ N /254⌉ bytes one byte in 254 drove. Consequently, the transmission time code of the sequence of bytes is very predictable, making the cob is useful for real-time applications, where jitter can be problematic. The algorithm is computational inexpensive and average overhead costs are low in comparison with other algorithms an unambiguous framing.
However, cobs, requires up to 254 bytes lookahead. Before you pass it on the first byte, it needs to know the position of the first null byte if next 254 bytes.

1. The framing of packets and stuffing. (Обрамление пакетов и вброс)
When the packaged data is transmitted through any serial medium, which Protocol is required to define the packages. This is done through framing the token, a special bit-sequence or a character value that indicates where the boundaries between packages to fall. Stuffing data is the process of converting data packets before transmission to eliminate all occurrences of the framing marker, so that when the receiver detects a marker, you can be sure that the marker indicates the border between the packages.
Cobs converts an arbitrary string of bytes in the range. Having eliminated all zero bytes from the data, the null byte can be unambiguously mark the end converted data. This can be done by adding a null byte in the transformed data, thus forming a package consisting of cobs-encoded data payload to clearly identify the end of a batch.
Any other byte value could be reserved in the separator between the packets, but using zero simplifies the description.
There are two equivalent ways of describing the encoding process of the cobs:
Prefixed block description To encode some bytes, first append a zero byte, then break them into groups of either 254 non-zero bytes, or 0–253 non-zero bytes followed by a zero byte. Because of the appended zero byte, this is always possible. Encode each group by deleting the trailing zero byte if any and prepending the number of non-zero bytes, plus one. Thus, each encoded group is the same size as the original, except that 254 non-zero bytes are encoded into 255 bytes by prepending a byte of 255. As a special exception, if a packet ends with a group of 254 non-zero bytes, it is not necessary to add the trailing zero byte. This saves one byte in some situations. Linked list description First, insert a zero byte at the beginning of the packet, and after every run of 254 non-zero bytes. This encoding is obviously reversible. It is not necessary to insert a zero byte at the end of the packet if it happens to end with exactly 254 non-zero bytes. Second, replace each zero byte with the offset to the next zero byte, or the end of the packet. Because of the extra zeros added in the first step, each offset is guaranteed to be at most 255.

2. Examples of coding. (Примеры кодирования)
These examples show how a different sequence of data encoded according to the algorithm on the cob. In the examples, all the bytes are expressed in hexadecimal values, and the encoded data is shown with the text formatting, illustrating the various functions:
Red is a byte, which is also the group header bytes containing the offset to the next group, but does not correspond to a data byte. They appear in two places: at the beginning of each coded packet, and after each group of 254 non-zero bytes.
There is a blue zero byte at the end of every packet to indicate the end of a packet to the data receiver. This package byte delimiter is not part of a proper cob, this additional framing bytes, which is added to the encoded output.
Green indicates zero bytes of data that have been changed by encoding. All the zero bytes are replaced by encoding the offset to the next zero byte, i.e. one plus the number of non-zero bytes that follow. This is actually a pointer to the next byte of the packet, which requires interpretation: if the addressed byte is nonzero, this is the next group header byte, data byte, which indicates the next byte that require interpretation, if the addressed byte is zero, this is the end of the package.
Bold indicates data bytes that were not modified by encoding. All non-zero data bytes remain unchanged.
Here is a diagram, on the example 3 from the table above to show how each changed byte of data is, and how it is identified as a data byte or an end byte of the frame.
: Location of end-of-packet zero symbol. 0 1 2 3 4 5: Byte Position 03 11 22 02 33 00: COBS Data Frame 11 22 00 33: Extracted Data OHB = Overhead Byte Points to next zero symbol EOP = End Of Packet
Examples 7 through 10 show how the overhead varies with the data encoded for the length of the packet is 255 or more.

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