Ruby 1.9：带有未知输入编码的正则表达式 [英] Ruby 1.9: Regular Expressions with unknown input encoding

问题描述

有没有一种被接受的方式来处理Ruby 1.9中的正则表达式，其输入的编码是未知的？假设我的输入是UTF-16编码的：

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)

我目前的方法是在内部使用UTF-8并在必要时对输入进行重新编码（复制）：

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

if y.methods.include?(:encode)  # 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">

但是，这对我来说有点尴尬，我想问一个更好的方法做它。

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

推荐答案

据我所知，没有更好的方法使用。但是，我可以建议稍微改动吗？

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

为了不改变正则表达式的编码，而不是改变输入的编码？

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)

在病理情况下（输入编码每行改变） ，因为你通过循环每次重新编码正则表达式。但是在99.9％的情况下，编码对于数百或数千行的整个文件是不变的，这将导致重新编码的大幅减少。

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.

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