This code is hereby placed in the public domain.
Please send comments, suggestions, and bug reports to lhf@tecgraf.puc-rio.br.
This is a simple Lua library for packing and unpacking binary data.
The library adds two functions to the string library: pack and unpack.
Prototype:
ret = pack( F, x1, x2, ... )
Description:
Packs binary data into a string.
Parameters:
FA string describing how the values
x1, x2, ...are to be interpreted and formatted. Each letter in the format stringFconsumes one of the given values. The letter codes understood by pack are listed below (they are inspired by Perl's codes but are not the same). Numbers following letter codes inFindicate repetitions.
x1, x2, ...Values to pack into binary. Only values of type number or string are accepted.
Returns:
retA (binary) string containing the values packed as described in
F.
Prototype:
val, next = unpack( s, F [,init] )
Description:
Packs binary data into a string.
Parameters:
sA (binary) string containing data packed as if by pack.
FA format string describing what is to be read from
s
initAn optional init marks where in
sto begin reading the values.
Returns:
nextThe first value returned by unpack is the next unread position in
s, which can be used as the init position in a subsequent call tounpack. This allows you tounpackvalues in a loop or in several steps. If the position returned byunpackis beyond the end ofs, thenshas been exhausted; any calls tounpackstarting beyond the end ofswill always returnnilvalues.
valOne value per letter in
FuntilForsis exhausted (the letters codes are the same as for pack, except that numbers followingAare interpreted as the number of characters to read into the string, not as repetitions).
z: zero-terminated string
p: string preceded by length byte
P: string preceded by length word
a: string preceded by length size_t
A: string
f: float
d: double
n: Lua number
c: char
b: byte (unsigned char)
h: short
H: unsigned short
i: int
I: unsigned int
l: long
L: unsigned long
<: little endian
>: big endian
=: native endian