I am writing a wireshark dissector of a custom protocol using LUA.For this custom protocol,there are no underlying TCP port or UDP port hence i have written a postdissector.
I am able to capture the payload from the below layers and convert it into a string.
local io_b = tostring(customprotocol)
After this, io_b has the following data
io_b = 10:10:10:10:01:0f:00:0d:00:00:00:00:01:00:00:00:00:20:0a:00:00
At first I split this string with : as the seperator and copy the elements into an array/table.
datafields = {}
index = 1
for value in string.gmatch(io_b, "[^:]+") do
datafields[index] = value
index = index + 1
end
Then I read each element of the datafield array as a uint8 value and check if a bit is set in that datafield element.How to make sure that each element of the table is uint8?
function lshift(x, by)
return x * 2 ^ by
end
--checks if a bit is set at a position
function IsBitSet( b, pos)
if b ~= nil then
return tostring(bit32.band(tonumber(b),lshift(1,pos)) ~= 0)
else
return "nil"
end
end
Then I want to display the value of each bit in the wireshark.I dont care about the first four bytes. The script displays each bit of the 5th byte(which is the 1st considered byte) correctly but displays all the bits value of the 6th byte and other remaining bytes as "nil".
local data_in_2 = subtree:add(customprotocol,"secondbyte")
data_in_2:add(firstbit,(IsBitSet((datafields[6]),7)))
data_in_2:add(secondbit,(IsBitSet((datafields[6]),6)))
data_in_2:add(thirdbit,(IsBitSet((datafields[6]),5)))
data_in_2:add(fourbit,(IsBitSet((datafields[6]),4)))
data_in_2:add(fivebit,(IsBitSet((datafields[6]),3)))
data_in_2:add(sixbit,(IsBitSet((datafields[6]),2)))
data_in_2:add(sevenbit,(IsBitSet((datafields[6]),1)))
data_in_2:add(eightbit,(IsBitSet((datafields[6]),0)))
What am i doing wrong?
Maybe i am wrong but it seems you can do it simpler with...
io_b = '10:10:10:10:01:0f:00:0d:00:00:00:00:01:00:00:00:00:20:0a:00:00'
-- Now replace all : on the fly with nothing and convert it with #Egor' comment tip
-- Simply by using string method gsub() from within io_b
b_num = tonumber(io_b:gsub('%:', ''), 16)
print(b_num)
-- Output: 537526272
#shakingwindow - I cant comment so i ask here...
Do you mean...
io_b = '10:10:10:10:01:0f:00:0d:00:00:00:00:01:00:00:00:00:20:0a:00:00'
-- Converting HEX to string - Replacing : with ,
io_hex = io_b:gsub('[%x]+', '"%1"'):gsub(':', ',')
-- Converting string to table
io_hex_tab = load('return {' .. io_hex .. '}')()
-- Put out key/value pairs by converting HEX value string to a number on the fly
for key, value in pairs(io_hex_tab) do
print(key, '=', tonumber(value, 16))
end
...that puts out...
1 = 16
2 = 16
3 = 16
4 = 16
5 = 1
6 = 15
7 = 0
8 = 13
9 = 0
10 = 0
11 = 0
12 = 0
13 = 1
14 = 0
15 = 0
16 = 0
17 = 0
18 = 32
19 = 10
20 = 0
21 = 0
...?
Related
I'm doing some codewars and arr[index] keeps returning nil. I've done this a few different ways, and I'm sure the array exists, as well as the index. What's wrong here, is it syntax?
As I've mentioned in the title, I want to find the last digit of the array.
if arr[index] <= 0 then
return -1
end
Full Code:
local solution = {}
function solution.newAvg(arr, navg)
local currentAverage = 0
local index = 0
for i, v in pairs(arr) do
index = i
currentAverage = currentAverage + v
end
if arr[index] <= 0 then
return -1
end
return math.ceil(((index+1) * navg) - currentAverage)
end
return solution
I see two issues with your code:
Edge case: Empty array
If arr = {}, the loop for i, v in pairs(arr) do won't execute at all and index will remain at 0. Since arr is empty, arr[0] will be nil and arr[index] <= 0 will fail with an "attempt to compare a nil value" error.
Lack of ordering guarantee
You use pairs rather than ipairs to loop over what I assume is a list. This means keys & values might be traversed in any order. In practice pairs usually (but not always!) traverses the list part of a table in the same order as ipairs, but the reference manual clearly states that you can't rely on no specific order. I don't think CodeWars is this advanced but consider the possibility that pairs may be overridden to deliberately shuffle the order of traversal in order to check whether you're relying on the dreaded "undefined behavior". If this is the case, your "last index" might actually be any index that happens to be visited last, obviously breaking your algorithm.
Fixes
I'll assume arr is an "array", that is, it only contains keys from 1 to n and all values are non-nil (i.e. there are no holes). Then you can (and should!) use ipairs to loop over the "array":
for i, v in ipairs(arr) do ... end
I don't know the problem statement so it's hard to tell how an empty array should be handled. I'll assume that it should probably return 0. You could add a simply early return at the top of the function for that: if arr[1] == nil then return 0 end. Nonempty arrays will always have arr[1] ~= nil.
I want to find the last digit of the array.
If you mean the last integer (or entry/item) of the array:
local last = array[#array]
If you mean the last digit (for example array = {10, 75, 44, 62} and you want 2), then you can get the last item and then get the last digit using modulo 10:
local last = array[#array] % 10
for i, v in pairs(arr) do
index = i
currentAverage = currentAverage + v
end
Just a reminder:
#array returns the number of items in a table.
In Lua, arrays are implemented using integer-indexed tables.
There's a difference between pairs() and ipairs().
Regarding point 3 above, the following code:
local array = {
[1] = 12,
[2] = 32,
[3] = 41,
[4] = 30,
[5] = 14,
[6] = 50,
[7] = 62,
[8] = 57
}
for key, value in pairs(array) do
print(key, value)
end
produces the following output (note that the order of keys is not respected):
8 57
1 12
2 32
3 41
4 30
5 14
6 50
7 62
while the same code above with pairs() replaced with ipairs() gives:
1 12
2 32
3 41
4 30
5 14
6 50
7 62
8 57
So, this might be the cause of your problem.
Quick explanation, I have recently started using codewars to further improve my programming skills and my first challenge was to make a roman numeral decoder, I went through many versions because I wasnt satisfied with what I had, So I am asking if there is an easier way of handling all the patterns that roman numerals have, for example I is 1 but if I is next to another number it takes it away for example V = 5 but IV = 4.
here is my CODE:
function Roman_Numerals_Decoder (roman)
local Dict = {I = 1, V = 5, X = 10, L = 50, C = 100, D = 500, M = 1000}
local number = 0
local i = 1
while i < #roman + 1 do
local letter = roman:sub(i,i) -- Gets the current character in the string roman
if roman:sub(i,i) == "I" and roman:sub(i + 1,i + 1) ~= "I" and roman:sub(i + 1,i + 1) ~= "" then -- Checks for the I pattern when I exists and next isnt I
number = number + (Dict[roman:sub(i +1,i + 1)] - Dict[roman:sub(i,i)]) -- Taking one away from the next number
i = i + 2 -- Increase the counter
else
number = number + Dict[letter] -- Adds the numbers together if no pattern is found, currently checking only I
i = i + 1
end
end
return number
end
print(Roman_Numerals_Decoder("MXLIX")) -- 1049 = MXLIX , 2008 = MMVIII
at the moment I am trying to get 1049 (MXLIX) to work but I am getting 1069, obviously I am not following a rule and I feel like its more wrong then it should be because usually if its not correct its 1 or 2 numbers wrong.
The algorithm is slightly different: you need to consider subtraction when the previous character has less weight than the next one.
function Roman_Numerals_Decoder (roman)
local Dict = {I = 1, V = 5, X = 10, L = 50, C = 100, D = 500, M = 1000}
local num = 0
local i = 1
for i=1, #roman-1 do
local letter = roman:sub(i,i) -- Gets the current character in the string roman
local letter_p = roman:sub(i+1,i+1)
if (Dict[letter] < Dict[letter_p]) then
num = num - Dict[letter] -- Taking one away from the next number
print("-",Dict[letter],num)
else
num = num + Dict[letter] -- Adds the numbers together if no pattern is found, currently checking only I
print("+",Dict[letter],num)
end
end
num = num + Dict[roman:sub(-1)];
print("+",Dict[roman:sub(-1)], num)
return num
end
print(Roman_Numerals_Decoder("MXLIX")) -- 1049 = MXLIX , 2008 = MMVIII
Failed Spacing
I'm trying to get all of these names with a max char of 31 to line up all together in the same row by adding the number of spaces per player name that it needs. I've been trying to accomplish this for some time now and I just can't figure this out completely.
This is my current code which is a disaster I know..
local c = client.GetPlayerNameByIndex(i)
if c ~= nil and client.GetPlayerNameByIndex(i) ~= "nil" then
playerlist[i] = all_trim(client.GetPlayerNameByIndex(i))
local leve = 67
local namelength = #client.GetPlayerNameByIndex(i) --max 31 chars
local output = "" .. client.GetPlayerNameByIndex(i)
local newspace = ""
local neededspaces = 31 - #client.GetPlayerNameByIndex(i)
print(neededspaces)
for i=1, 31-#string.sub(client.GetPlayerNameByIndex(i), 1, 31) do
newspace = newspace .. " "
end
playerinfolist[i] = output .. newspace .. "a"
end
In simple terms I want all of the "a"s to line up with each string. Thanks for helping me!
I run this code in lua:
cal = {num1 = 0, num2 = 0, num3 = 0,num4 = 0,num5 = 0,num6 = 0}
function cal:new (n1,n2,n3,n4,n5,n6)
local self = {}
setmetatable(self,cal)
self.num1 = n1
self.num2 = n2
self.num3 = n3
self.num4 = n4
self.num5 = n5
self.num6 = n6
return self
end
ea = cal:new(1,2,3,4,5,6)
ae = cal:new(7,8,9,10,11,12)
for k,va in pairs(ea) do print(va) end
for k,va in pairs(ae) do print(va) end
and this is the output:
1 2 5 6 3 4 7 8 11 12 9 10
why this numbers has been messed up???
pairs traverses a table in an unspecified order.
The manual says
The order in which the indices are enumerated is not specified, even for numeric indices.
(That's in the entry for next, on which pairs is based.)
Lua does not store table keys in any particular order. One way to print fields in order would be to add another method:
function cal:print()
print(self.num1)
print(self.num2)
print(self.num3)
print(self.num4)
print(self.num5)
print(self.num6)
end
I'm learning lua and I want to arrange my bubble picture with some specific x and y coordinates, here's my code so far, the value of my j and i is only incrementing by 1 instead of the +29, I know I'm lacking some knowledge so any help will be appreciated
local background = display.newImageRect("blueBackground.png",642, 1040)
background.x = display.contentCenterX
background.y = display.contentCenterY
local x = 15
local y=15
for i=15,25 do
for j=15, 25 do
local bubble = display.newImageRect("bubble.png", 23,23)
bubble.x = i
bubble.y = j
j = j + 29
print("j",j)
end
i = i + 29
print("i",i)
end
This should helps you.
From Lua documentation
The for statement has two variants: the numeric for and the
generic for.
A numeric for has the following syntax:
for var=exp1,exp2,exp3 do
something
end
That loop will execute something for each value of var from exp1
to exp2, using exp3 as the step to increment var. This third
expression is optional; when absent, Lua assumes one as the step
value. As typical examples of such loops, we have
for i=1,f(x) do print(i) end
for i=10,1,-1 do print(i) end
Use
for i=15, 29*10+15, 29 do
for j=15, 29*10+15, 29 do
local bubble = display.newImageRect("bubble.png", 23,23)
bubble.x = i
bubble.y = j
print("j",j)
end
print("i",i)
end
or
for i=0, 10 do
for j=0, 10 do
local bubble = display.newImageRect("bubble.png", 23,23)
bubble.x = 15 + i * 29
bubble.y = 15 + j * 29
...