add lua script experiment for encoding/decoding base32/58

Signed-off-by: Jakub Sokołowski <jakub@status.im>

nginx-lua/b32tob58.lua

@@ -0,0 +1,130 @@
+--------------------------------------------------------------------------------
+-- encoding configuration
+--------------------------------------------------------------------------------
+
+local base48Alphabet = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz"
+local base32Alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567"
+local base32PadMap = { "", "======", "====", "===", "=" }
+
+--------------------------------------------------------------------------------
+-- encoding function for base58
+--------------------------------------------------------------------------------
+
+local function encode_base58(s)
+	local q, b
+	local et = {}
+	local zn = 0 	-- number of leading zero bytes in s
+	-- assume s is a large, little-endian binary number
+	-- with base256 digits (each byte is a "digit")
+	local nt = {} -- number to divide in base 256, big endian
+	local dt = {} -- result of nt // 58, in base 256
+	local more = true  -- used to count leading zero bytes
+	for i = 1, #s do
+		b = string.byte(s, i)
+		if more and b == 0 then
+			zn = zn + 1
+		else
+			more = false
+		end
+		nt[i] = b
+	end
+	if #s == zn then --take care of strings empty or with only nul bytes
+		return string.rep('1', zn)
+	end
+	more = true
+	while more do
+		local r = 0
+		more = false
+		for i = 1, #nt do
+			b = nt[i] + (256 * r)
+			q = b // 58
+			-- if q is not null at least once, we are good
+			-- for another division by 58
+			more = more or q > 0
+			r = b % 58
+			dt[i] = q
+		end
+		-- r is the next base58 digit. insert it before previous ones
+		-- to get a big-endian base58 number
+		table.insert(et, 1, string.char(string.byte(base48Alphabet, r+1)))
+		-- now copy dt into nt before another round of division by 58
+		nt = {}
+		for i = 1, #dt do nt[i] = dt[i] end
+		dt = {}
+	end--while
+	-- don't forget the leading zeros ('1' is digit 0 in bitcoin base58 alphabet)
+	return string.rep('1', zn) .. table.concat(et)
+end
+
+--------------------------------------------------------------------------------
+-- various helpers for base32 decoding
+--------------------------------------------------------------------------------
+
+local function number_to_bit( num, length )
+   local bits = {}
+
+   while num > 0 do
+      local rest = math.floor( math.fmod( num, 2 ) )
+      table.insert( bits, rest )
+      num = ( num - rest ) / 2
+   end
+
+   while #bits < length do
+      table.insert( bits, "0" )
+   end
+
+   return string.reverse( table.concat( bits ) )
+end
+
+local function ignore_set( str, set )
+   if set then
+      str = str:gsub( "["..set.."]", "" )
+   end
+   return str
+end
+
+local function pure_from_bit( str )
+   return ( str:gsub( '........', function ( cc )
+               return string.char( tonumber( cc, 2 ) )
+            end ) )
+end
+
+local function unexpected_char_error( str, pos )
+   local c = string.sub( str, pos, pos )
+   return string.format( "unexpected character at position %d: '%s'", pos, c )
+end
+
+--------------------------------------------------------------------------------
+-- generic function to decode and encode base32/base64
+--------------------------------------------------------------------------------
+
+local function from_basexx( str, alphabet, bits )
+   local result = {}
+   for i = 1, #str do
+      local c = string.sub( str, i, i )
+      if c ~= '=' then
+         local index = string.find( alphabet, c, 1, true )
+         if not index then
+            return nil, unexpected_char_error( str, i )
+         end
+         table.insert( result, number_to_bit( index - 1, bits ) )
+      end
+   end
+
+   local value = table.concat( result )
+   local pad = #value % 8
+   return pure_from_bit( string.sub( value, 1, #value - pad ) )
+end
+
+function decode_base32( str, ignore )
+   str = string.upper(str)
+   str = ignore_set( str, ignore )
+   return from_basexx( string.upper( str ), base32Alphabet, 5 )
+end
+
+--------------------------------------------------------------------------------
+-- testing
+--------------------------------------------------------------------------------
+
+print(encode_base58('test'))
+print(decode_base32('ORSXG5A='))