[OpenWrt-Devel] [RFC] libubox/binary.h design proposal

[Javier Domingo Cansino]

Hello,

I asked Friday on IRC how to write blobs, I was suggested using
blob_raw_put from libubox/blob.h, but as I have to implement a binary
protocol that uses different endianess, non aligned data etc., I think the
best solution is creating a set of helper functions to write/read blobs.

As this is quite generic library, there might already exist some work done
that I am missing (please link!). I would love to have feedback from this
design before typing code.

I have started my work on github[1], which is basically a header file with
the following comment and some prototype ideas. The syntax I have thought
is described there, but it basically follows a printf syntax, allowing raw
chars to be written.

Cheers!

/*
 * Syntax for the function is as follows.
 *   %[n][a][lb][01r]{i,y,w,d,q,s}
 *
 *   All the characters that don't follow this will be treated as raw chars
 *   to be written as they are.
 *
 * Data type
 *   * i - bit
 *   * y - byte
 *   * w - 2 byte word
 *   * d - 4 byte word
 *   * q - 8 byte word
 *   * s - string without termination (use strlen()+1 in quantity to null)
 *
 * Data value
 *   * 0 - fill the specified space with zeros
 *   * 1 - fill the specified space with ones
 *   * r - fill the specified space with random data
 *
 *   String data type is not valid in this case
 *
 * Endianess. No conversion by default
 *   * l - little endian
 *   * b - big endian
 *
 * Alignment. No alignment by default
 *   * a - align this to it's datatype
 *         bits are aligned to byte
 *
 * Quantity. One by default
 *   * n - number of same datatype (placed together)
 *         this denotes length of string, padded with 0
 *
 * Some examples:
 *   * %4lw - 4 little endian 2 byte word
 *   * %2i  - 2 bits 'ab' from value b'000000ab'
 *   * %2bi - 2 bits 'ab' from value b'000000ba'
 *   * %2li - 2 bits 'ab' from value b'ab000000'
 *
 */


[1] Github branch: https://github.com/txomon/libubox
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