Lua - decodeURI (luvit)

This is trivial to do yourself in Lua if you understand the URI percent-encoded format. Each %XX substring represents UTF-8 data encoded with a % prefix and a hexadecimal octet.

local decodeURI
do
    local char, gsub, tonumber = string.char, string.gsub, tonumber
    local function _(hex) return char(tonumber(hex, 16)) end

    function decodeURI(s)
        s = gsub(s, '%%(%x%x)', _)
        return s
    end
end

print(decodeURI('%D0%BF%D1%80%D0%B8%D0%B2%D0%B5%D1%82'))

Here is another take. This code will save you lots of function calls if you have to decode many strings.

local hex = {}
for i = 0, 255 do
    hex[string.format("%02x", i)] = string.char(i)
    hex[string.format("%02X", i)] = string.char(i)
end

local function decodeURI(s)
    return (s:gsub('%%(%x%x)', hex))
end

print(decodeURI('%D0%BF%D1%80%D0%B8%D0%B2%D0%B5%D1%82'))