lua urlencode/urldecode

urldecode_encode.lua

    function encodeURI(str)
		if (str) then
			str = string.gsub (str, "\n", "\r\n")
			str = string.gsub (str, "([^%w ])",
				function (c) return string.format ("%%%02X", string.byte(c)) end)
			str = string.gsub (str, " ", "+")
	   end
	   return str
	end
	
	function decodeURI(s)
		if(s) then
			s = string.gsub(s, '%%(%x%x)', 
				function (hex) return string.char(tonumber(hex,16)) end )
		end
		return s
	end

You should add this line at line 13 :

s = string.gsub(s, "+", " ")

Line 4 is not the right regex for url safe characters. This code will incorrectly % encode the characters . _ - ~ even though they are already safe per https://tools.ietf.org/html/rfc3986#section-2.3. The correct one would be

str = string.gsub(str, "([^%w _ %- . ~])",
    function (c) return string.format ("%%%02X", string.byte(c)) end)