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I am trying to find a way in Ruby to take a UTF-8 byte array and transform it back to a string.

In irb (Ruby 1.9.2 preview 3) I can create the correct byte array from UTF-8 string: 

ruby-1.9.2-preview3 > 'Café'.bytes.to_a
 => [67, 97, 102, 195, 169]

However, I can't find a way to roundtrip from bytes back to an array. I tried to use Array.pack with the U* option, but that doesn't work for multibyte characters.

ruby-1.9.2-preview3 > [67, 97, 102, 195, 169].pack('U*')
 => "Café"

Does anybody know a way to take a UTF-8 byte array with multibyte characters and convert it back to a string?

Thanks.

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2 Answers 2

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34

This has to do with how pack interprets its input data. The U* in your example causes it to convert the input data (assumed to be in a default character set, I assume; I really couldn't find any documentation of this) to UTF-8, thus the double encoding. Instead, just pack the bytes and interpret as UTF-8:

irb(main):010:0> [67, 97, 102, 195, 169].pack('C*').force_encoding('utf-8')
=> "Café"
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Comments

11

You specifically ask about a byte array, but maybe codepoints are more suitable:

ar = 'Café'.codepoints.to_a
# => [67, 97, 102, 233]
ar.pack('U*')
# => Café
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1 Comment

I might use that on another project, but for this one I start out with the byte array, and have to work back to the string.

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