Implementation of binary packing/unpacking in pure lua
luarocks install lua-struct
You can use it to pack and unpack binary data in pure lua. The idea is very similar to PHP unpack and pack functions.
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.
"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).
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