Programming Tutorials

encoding and decoding in Ruby using Base64 Module

By: Emiley J. in Ruby Tutorials on 2009年03月03日 [フレーム]

The Base64 module provides for the encoding (encode64) and decoding (decode64) of binary data using a Base64 representation.

The following particular features are also provided:

• encode into lines of a given length (b64encode)
• decode the special format specified in RFC2047 for the representation of email headers (decode_b)

Example

A simple encoding and decoding.

 require "base64"
 enc = Base64.encode64('Send reinforcements')
 # -> "U2VuZCByZWluZm9yY2VtZW50cw==\n"
 plain = Base64.decode64(enc)
 # -> "Send reinforcements"

The purpose of using base64 to encode data is that it translates any binary data into purely printable characters. It is specified in RFC 2045 (www.faqs.org/rfcs/rfc2045.html).

Prints the Base64 encoded version of bin (a String) in lines of len (default 60) characters.

 require 'base64'
 data = "Now is the time for all good coders\nto learn Ruby"
 puts Base64.b64encode(data)

Generates:

 Tm93IGlzIHRoZSB0aW1lIGZvciBhbGwgZ29vZCBjb2RlcnMKdG8gbGVhcm4g
 UnVieQ==

# File base64.rb, line 112
 def b64encode(bin, len = 60)
 encode64(bin).scan(/.{1,#{len}}/o) do
 print $&, "\n"
 end
 end

Returns the Base64-decoded version of str.

 require 'base64'
 str = 'VGhpcyBpcyBsaW5lIG9uZQpUaGlzIG' +
 'lzIGxpbmUgdHdvClRoaXMgaXMgbGlu' +
 'ZSB0aHJlZQpBbmQgc28gb24uLi4K'
 puts Base64.decode64(str)

Generates:

 This is line one
 This is line two
 This is line three
 And so on...

# File base64.rb, line 58
 def decode64(str)
 str.unpack("m")[0]
 end

Decodes text formatted using a subset of RFC2047 (the one used for mime-encoding mail headers).

Only supports an encoding type of 'b" (base 64), and only supports the character sets ISO-2022-JP and SHIFT_JIS (so the only two encoded word sequences recognized are =?ISO-2022-JP?B?-= and =?SHIFT_JIS?B?-=). Recognition of these sequences is case insensitive.

# File base64.rb, line 72
 def decode_b(str)
 str.gsub!(/=\?ISO-2022-JP\?B\?([!->@-~]+)\?=/i) {
 decode64(1ドル)
 }
 str = Kconv::toeuc(str)
 str.gsub!(/=\?SHIFT_JIS\?B\?([!->@-~]+)\?=/i) {
 decode64(1ドル)
 }
 str = Kconv::toeuc(str)
 str.gsub!(/\n/, ' ') 
 str.gsub!(/0円/, '')
 str
 end

Returns the Base64-encoded version of str.

 require 'base64'
 Base64.b64encode("Now is the time for all good coders\nto learn Ruby")

Generates:

 Tm93IGlzIHRoZSB0aW1lIGZvciBhbGwgZ29vZCBjb2RlcnMKdG8gbGVhcm4g
 UnVieQ==

# File base64.rb, line 96
 def encode64(bin)
 [bin].pack("m")
 end

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