lua parsing after more than one byte - parsing

Question

how can I parse an binary after more than one byte?
for example:
56 30 30 31 07 00 00 00 EF BF BD EF BF BD 2A 5C EF BF BD 03 01 45 7E 12 02 EF BF BD 00 EF BF BD 1F 56 30 30 31 01 00 00 00 EF BF BD EF BF BD 2A 5C EF BF BD 03 02 45 24 56 30 30 31 04 00 00 00 EF BF BD EF BF BD 2A 5C EF BF BD 03 02 45 13 00 00 00 56 30 30 31 07 00 00 00 EF BF BD EF BF BD 2A 5C EF BF BD 03 01 45 7E 12 02 24 00 4D EF BF
I want to parse this after 0x56 0x30 0x30 0x31. How can I do this? Before every new 0x56 0x30 0x30 0x31 the old packet(string) should end.
like this:
56 30 30 31 07 00 00 00 EF BF BD EF BF BD 2A 5C EF BF BD 03 01 45 7E 12 02 EF BF BD 00 EF BF BD 1F
56 30 30 31 01 00 00 00 EF BF BD EF BF BD 2A 5C EF BF BD 03 02 45 24
56 30 30 31 04 00 00 00 EF BF BD EF BF BD 2A 5C EF BF BD 03 02 45 13 00 00 00
56 30 30 31 07 00 00 00 EF BF BD EF BF BD 2A 5C EF BF BD 03 01 45 7E 12 02 24 00 4D EF BF
I already did something simular for parsing after one byte into an table. But I can not change it into my new problem.
Thats the code for parsing after one Byte 0x7E.
function print_table(tab)
print("Table:")
for key, value in pairs(tab) do
io.write(string.format("%02X ", value))
end
print("\n")
end
local function read_file(path, callback)
local file = io.open(path, "rb")
if not file then
return nil
end
local t = {}
repeat
local str = file:read(4 * 1024)
for c in (str or ''):gmatch('.') do
if c:byte() == 0x7E then
callback(t) -- function print_table
t = {}
else
table.insert(t, c:byte())
end
end
until not str
file:close()
return t
end
local result = {}
function add_to_table_of_tables(t)
table.insert(result, t)
end
local fileContent = read_file("file.dat", print_table)
It is important that 56 30 30 31 is as first written in the string.
Thank your for your help!
I need it also with reading my input in from an file.
I am reading my file like this in:
local function read_file(path) --function read_file
local file = io.open(path, "rb") -- r read mode and b binary mode
if not file then return nil end
local content = file:read "*all" -- *all reads the whole file
file:close()
return content
end

Answer 1

You can use a gsub to replace the target substring with a single char unique to the input string, I will use \n for this example. after that you can use gmatch where it selects a run of char that are not the substituted char.
local input = [[56 30 30 31 07 00 00 00 EF BF BD EF BF BD 2A 5C EF BF BD 03 01 45 7E 12 02 EF BF BD 00 EF BF BD 1F 56 30 30 31 01 00 00 00 EF BF BD EF BF BD 2A 5C EF BF BD 03 02 45 24 56 30 30 31 04 00 00 00 EF BF BD EF BF BD 2A 5C EF BF BD 03 02 45 13 00 00 00 56 30 30 31 07 00 00 00 EF BF BD EF BF BD 2A 5C EF BF BD 03 01 45 7E 12 02 24 00 4D EF BF]]
local pattern ="([^\n]+)"
local rowPrefix = "56 30 30 31"
input = input:gsub(rowPrefix, "\n")
for row in input:gmatch(pattern) do
print(rowPrefix .. row)
end
Output:
56 30 30 31 07 00 00 00 EF BF BD EF BF BD 2A 5C EF BF BD 03 01 45 7E 12 02 EF BF BD 00 EF BF BD 1F
56 30 30 31 01 00 00 00 EF BF BD EF BF BD 2A 5C EF BF BD 03 02 45 24
56 30 30 31 04 00 00 00 EF BF BD EF BF BD 2A 5C EF BF BD 03 02 45 13 00 00 00
56 30 30 31 07 00 00 00 EF BF BD EF BF BD 2A 5C EF BF BD 03 01 45 7E 12 02 24 00 4D EF BF
Resources for more information:
Programming in Lua: 20.1 – Pattern-Matching Functions
Lua 5.3 Reference Manual: string.gmatch
Lua 5.3 Reference Manual: string.gsub

Answer 2

Adapt this code:
S=[[56 30 30 31 07 00 00 00 EF BF BD EF BF BD 2A 5C EF BF BD 03 01 45 7E 12 02 EF BF BD 00 EF BF BD 1F 56 30 30 31 01 00 00 00 EF BF BD EF BF BD 2A 5C EF BF BD 03 02 45 24 56 30 30 31 04 00 00 00 EF BF BD EF BF BD 2A 5C EF BF BD 03 02 45 13 00 00 00 56 30 30 31 07 00 00 00 EF BF BD EF BF BD 2A 5C EF BF BD 03 01 45 7E 12 02 24 00 4D EF BF]]
H=[[56 30 30 31]]
E="\n"
S=S:gsub(H,E..H)
S:gsub(E.."([^"..E.."]+)",print)