NAME
PATRIM - the pack-trimmed format
DESCRIPTION
The PATRIM format is a simple format that allows to store data in binary form, where every data is identified by an ID, that represents either an unsigned integer or a blob/byte array.
Data are stored very simply : first the ID, then either the value for an integer, or the data length for a blob, in which case said data must immediately follow.
IDs and values/lengths are stored using the "pack trimmed" algorithm, as described in u64_pack_trim(3). Meaning the value is stored in little endian mode, but only the low 7 bits are used for the value, the most significant bit being a flag which, when set, indicates that another byte must be read and processed.
Any 64bit number can be written that way, packed into from 1 to 9 bytes, depending on the actual value.
The IDs are unsigned numbers to identify their associated value, with the least significant bit having a special meaning : if set, it represents a blob, otherwise an (unsigned) integer.
Helpers functions are available, either directly (e.g. patrim_put(3)) or when using a buffer (e.g. buffer_patrim_put(3)).
That is all.
FILE FORMATS
As a rule, any file whose content is encoded in PATRIM should first feature an header as such :
- A big-endian encoded 32bit magic number, to identify the specific file format.
The magic number should have certain bits set to indicate it is PATRIM
encoded, specifically :
(magic & 0xf0f0f000) = 0xa0e0f000 - Additionally, bit 8 is used as a flag to indicate whether or not the file contains shielded data, as described in shldata(5). When set, and shielded data are present, for every ID in the file its bit 7 is a flag which, when set, indicates the data are part of the shielded data protocol itself.
- A version number, pack-trimmed.
Helpers functions buffer_puthdr(3) and buffer_gethdr(3) are available to write and read such headers, respectively.