Base64 Strings in Ruby (bonus JS)

Working with Base64 in Ruby

There are several options for encoding and decoding Base64 strings in Ruby. Here are a couple that I’ve worked with in professional and personal projects.

The Base64 module

A Base64 module exists in Ruby to encode and decode Base64 strings. Open up irb and try it out:

require 'base64'

source_str = "A human-readable string with a smiley :)"
encoded_str = Base64.encode64(source_str)

Encoded, the string looks like this:

QSBodW1hbi1yZWFkYWJsZSBzdHJpbmcgd2l0aCBhIHNtaWxleSA6KQ==\n

The decoded version of the string should equal source_str exactly.

decoded_str = Base64.decode64(encoded_str)
source_str == decoded_str
# true

Decoding with String#unpack

The Ruby string method unpack decodes a string according to whatever formatting option you pass as a parameter. It returns an array of values, the length of which depends on how you decode the string.

To use this method for Base64 decoding, pass 'm*' as the parameter. We can expect an array of size 1.

Let’s try this on the encoded string we created above.

unpacked_str = encoded_str.unpack('m*')

The returned value should be:

[“A human-readable string with a smiley :)”]

Yup, that’s an array! Grabbing the first element should give us our original string.

decoded_str = unpacked_str[0]
decoded_str == source_str 
# => true

Encoding with Array#pack

To encode a string, we use the array method pack. It also accepts 'm*' as the directive to use Base64 encoding. This method will return the Base64 encoded string.

Here’s the slightly inconvenient part. Because pack is a method on Array, it will only work if the string we want to encode in Base64 is wrapped in an array.

source_str.pack('m*')
# => NoMethodError: undefined method `pack' for ...:String

[source_str].pack('m*')
# => "QSBodW1hbi1yZWFkYWJsZSBzdHJpbmcgd2l0aCBhIHNtaWxleSA6KQ==\n" 

unpacked_str.pack('m*')
# => "QSBodW1hbi1yZWFkYWJsZSBzdHJpbmcgd2l0aCBhIHNtaWxleSA6KQ==\n"

Bonus: Decoding Base64 in Javascript

Many browsers have built-in support for Base64 encoding/decoding in Javascript.

Open up a JS console and test it out. To encode a string, use the window function btoa (“b to a”).

var sourceStr = "A human-readable string with a smiley :)";

var encodedStr = btoa(sourceStr);
encodedStr
// < "QSBodW1hbi1yZWFkYWJsZSBzdHJpbmcgd2l0aCBhIHNtaWxleSA6KQ=="

And to decode that string, use atob.

var decodedStr = atob(encodedStr);
decodedStr
// < "A human-readable string with a smiley :)"