lua-struct

Implementation of binary packing/unpacking in pure lua

LuaRocks

luarocks install lua-struct

what is it for?

You can use it to pack and unpack binary data in pure lua. The idea is very similar to PHP unpack and pack functions.

byte order

You can use < or > at the beginning of the format string to specify the byte order. Default is little endian (<), but you can change it to big endian (>) as well. It is possible to dynamically change the byte order within the format string, so in general you can save types in different byte orders.

available types

"b" a signed char.
"B" an unsigned char.
"h" a signed short (2 bytes).
"H" an unsigned short (2 bytes).
"i" a signed int (4 bytes).
"I" an unsigned int (4 bytes).
"l" a signed long (8 bytes).
"L" an unsigned long (8 bytes).
"f" a float (4 bytes).
"d" a double (8 bytes).
"s" a zero-terminated string.
"cn" a sequence of exactly n chars corresponding to a single Lua string (if n <= 0 then for packing - the string length is taken, unpacking - the number value of the previous unpacked value which is not returned).

how to use it?

local struct = require "struct"

local packed = struct.pack('<LIhBsbfd', 123456789123456789, 123456789, -3200, 255, 'Test message', -1, 1.56789, 1.56789)
local L, I, h, B, s, b, f, d = struct.unpack('<LIhBsbfd', packed)
print(L, I, h, B, s, b, f, d)

1.2345678912346e+017    123456789    -3200    255    Test message    -1    1.5678899288177    1.56789