PKT XML Archive Specification 1.6

This document describes a packetized file format for storing data for a set of files.

In operation, a user will select a set of files from which the packet data is to be made. These are known as input files. The user will provide these to a program which generates file(s) that match the specification in this document. The program is known as the PKT Client or client for short, and the generated files are known as PKT files. If the PKT files ever get damaged (e.g. when they are transmitted or stored on a faulty disk) the client can read the (possibly damaged) PKT files, and regenerate the original input files. Of course, not all damages can be repaired, but many can.

PKT files consist of input file data, recovery data and other data stored in a simple, easily readable format. The PKT file itself is made of packets - self-contained parts with their own checksum. This design prevents damage to one part of the file from making the whole file unusable.

Packets have only one type and may be used in different ways depending on the filters specified. A PKT file is only required to contain 1 packet per file. They may consist of more than one and may also be added (merged) together in any order.

There are no conventions used in the design of this specification.

A PKT file consists of a sequence of "packets". A packet has a variable length body and can be either binary or ASCII encoded. All packets are pure XML and are all of variable length. If the client does not understand the packet, the packet is ignored. To be compliant with this specification, a client must understand only 2 algorithms - the BZIP2 compression algorithm and the UUEncoder algorithm.

The packet header and footer is:

<?xml version="1.0" encoding="UTF-8"?>
<PKT>

Footer :
</PKT>

For BZIPped binary packets the packet header is :

<PKTBZ>

and footer :

<BZPKT>

Similarly the two bytes denote other types of binary packets, e.g. GZ for GZIPped binary packets. Note that stripping out the data between the two blocks and decompressing with the algorithm specified will produce the exact same format as shown on the uncompressed packet header and footer i.e. <PKT> ... </PKT>
.

The main packet :

<NAME>1090864802210</NAME> This is a file name, random string or unique ID depending on the packet type.

Attributes allow global settings for the packet being processed.
<ATTRIBUTES>
<TYPE>PARITY</TYPE> Type of packet can be PARITY, DATA or any other identifier.
For DATA packets the following attributes are also needed :
<DATASTART>0</DATASTART> This gives the start position in the file.
<DATAEND>7000</DATAEND> This gives the end position in the file. This allows files to be split into tiny pieces.
</ATTRIBUTES>

Filters are then applied on the packet data in sequence to produce the resulting data from the packet.
<FILTERLIST> A list of filters which will be applied in series to decode the packet data.
<FILTER index="0">
<ID>UUE</ID> UU Encoding filter. This denotes the packet data is UUEncoded.
</FILTER>
<FILTER index="1">
<ID>BZIP2</ID> After the data is UUDecoded it must be unBZIPped.
</FILTER>
<FILTER index="2">
<ID>LDPCXX,20</ID> This denotes the LDPC parity check code algorithm with the arguments specified is to be run on the reuslting data. This allows the current packet to recover data.
<ARGS index="0">/pkt/pktspec/pkt-spec.html,80239,2089346839</ARGS><ARGS index="1" /><ARGS index="2" /><ARGS index="3"/><ARGS index="4" /><ARGS index="5" /><ARGS index="6" /><ARGS index="7" /><ARGS
index="8" /><ARGS index="9" /><ARGS index="10" /><ARGS index="11" /><ARGS index
="12" /><ARGS index="13" /><ARGS index="14" /><ARGS index="15" /><ARGS index="16
" /><ARGS index="17" /><ARGS index="18" /> This list of args is passed directly into the LDPC algorithm.
</FILTER></FILTERLIST>

Every packet has a RIPEMD-160 bit checksum to ensure the packet is not corrupted.
<HASH>abaef69d118cd0fa2de359cef5a62e09a2608c20</HASH>

<BLOCKSIZE>199994</BLOCKSIZE> The datablock specifies how many bytes are required to process this packet fully in memory. All packets are loaded with blocksize allocated bytes to hold them. This guarantees there are only blocksize bytes of data between the datablock sections and any more or less will indicate a filter problem.

The actual packet data :

<DATABLOCK>begin 777 pkt
M0EIH.
`end
</DATABLOCK>

Finally the packet ends with the </PKT> footer.

This is the official spec. As can be seen PKT packets are self-describing and can be rebuilt by hand if necessary. Clients must ensure that all variations are taken into account and the XML decoder is not strict when processing the packet to ensure maximum recovery capability. Packets are normally encoded in UTF-8 but they may be in ASCII or other unicode formats. Cleints must ensure the header specified the encoding as shown.

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