Base64 Encoding in Lua

Our first example demonstrates base64 encoding and decoding in Lua. Here’s the full source code:

-- We'll use the base64 module from LuaRocks
local base64 = require("base64")

-- Here's the string we'll encode/decode
local data = "abc123!?$*&()'-=@~"

-- Encode using standard base64
local sEnc = base64.encode(data)
print(sEnc)

-- Decode the standard base64 string
local sDec = base64.decode(sEnc)
print(sDec)
print()

-- Lua doesn't have a built-in URL-safe base64 encoder,
-- so we'll create a simple function to make it URL-safe
local function urlsafe_b64encode(s)
    return (s:gsub('+', '-'):gsub('/', '_'))
end

local function urlsafe_b64decode(s)
    return (s:gsub('-', '+'):gsub('_', '/'))
end

-- Encode using URL-safe base64
local uEnc = urlsafe_b64encode(base64.encode(data))
print(uEnc)

-- Decode the URL-safe base64 string
local uDec = base64.decode(urlsafe_b64decode(uEnc))
print(uDec)

This script uses the base64 module, which you can install using LuaRocks:

$ luarocks install base64

Let’s break down the code:

1. We import the base64 module.

2. We define our input string data.

3. We use base64.encode() to encode the string and base64.decode() to decode it back.

4. Since Lua doesn’t have a built-in URL-safe base64 encoder, we create simple functions urlsafe_b64encode() and urlsafe_b64decode() to convert between standard and URL-safe base64.

5. We demonstrate URL-safe base64 encoding and decoding using these functions along with the standard base64 functions.

When you run this script, you should see output similar to this:

$ lua base64_encoding.lua
YWJjMTIzIT8kKiYoKSctPUB+
abc123!?$*&()'-=@~

YWJjMTIzIT8kKiYoKSctPUB-
abc123!?$*&()'-=@~

The string encodes to slightly different values with the standard and URL-safe base64 encoders (trailing + vs -), but they both decode to the original string as desired.

Note that in Lua, we had to create our own URL-safe base64 functions, as it’s not provided in the standard library. In a production environment, you might want to use a more robust implementation or a dedicated library for URL-safe base64 encoding.