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Ruby 1.9: Regular Expressions with unknown input encoding

开发者 https://www.devze.com 2022-12-14 09:24 出处:网络
Is there an accepted way to deal with regular expressions in Ruby 1.9 for which the encoding of the input is unknown? Let\'s say my input happens to be UTF-16 encoded:

Is there an accepted way to deal with regular expressions in Ruby 1.9 for which the encoding of the input is unknown? Let's say my input happens to be UTF-16 encoded:

x  = "foo<p>bar</p>baz"
y  = x.encode('UTF-16LE')
re = /<p>(.*)<\/p>/

x.match(re) 
=> #<MatchData "<p>bar</p>" 1:"bar">

y.match(re)
Encoding::CompatibilityError: incompatible encoding regexp match (US-ASCII regexp with UTF-16LE string)

My current approach is to use UTF-8 internally and re-encode (a copy of) the input if necessary:

if y.methods.include?(:e开发者_C百科ncode)  # Ruby 1.8 compatibility
  if y.encoding.name != 'UTF-8'
    y = y.encode('UTF-8')
  end
end

y.match(/<p>(.*)<\/p>/u)
=> #<MatchData "<p>bar</p>" 1:"bar">

However, this feels a little awkward to me, and I wanted to ask if there's a better way to do it.


As far as I am aware, there is no better method to use. However, might I suggest a slight alteration?

Rather than changing the encoding of the input, why not change the encoding of the regex? Translating one regex string every time you meet a new encoding is a lot less work than translating hundreds or thousands of lines of input to match the encoding of your regex.

# Utility function to make transcoding the regex simpler.
def get_regex(pattern, encoding='ASCII', options=0)
  Regexp.new(pattern.encode(encoding),options)
end



  # Inside code looping through lines of input.
  # The variables 'regex' and 'line_encoding' should be initialized previously, to
  # persist across loops.
  if line.methods.include?(:encoding)  # Ruby 1.8 compatibility
    if line.encoding != last_encoding
      regex = get_regex('<p>(.*)<\/p>',line.encoding,16) # //u = 00010000 option bit set = 16
      last_encoding = line.encoding
    end
  end
  line.match(regex)

In the pathological case (where the input encoding changes every line) this would be just as slow, since you're re-encoding the regex every single time through the loop. But in 99.9% of situations where the encoding is constant for an entire file of hundreds or thousands of lines, this will result in a vast reduction in re-encoding.


Follow the advice of this page: http://gnuu.org/2009/02/02/ruby-19-common-problems-pt-1-encoding/ and add

# encoding: utf-8

to the top of your rb file.

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