This class is a wrapper around File IO and Encoding that helps RDoc load files and convert them to the correct encoding.
Reads the contents of filename and handles any encoding
directives in the file.
The content will be converted to the encoding.  If the file
cannot be converted a warning will be printed and nil will be returned.
If force_transcode is true the document will be transcoded and
any unknown character in the target encoding will be replaced with ‘?’
# File lib/rdoc/encoding.rb, line 18
def self.read_file filename, encoding, force_transcode = false
  content = open filename, "rb" do |f| f.read end
  content.gsub!("\r\n", "\n") if RUBY_PLATFORM =~ %rmswin|mingw/
  utf8 = content.sub!(%r\A\xef\xbb\xbf/, '')
  RDoc::Encoding.set_encoding content
  if Object.const_defined? :Encoding then
    encoding ||= Encoding.default_external
    orig_encoding = content.encoding
    if utf8 then
      content.force_encoding Encoding::UTF_8
      content.encode! encoding
    else
      # assume the content is in our output encoding
      content.force_encoding encoding
    end
    unless content.valid_encoding? then
      # revert and try to transcode
      content.force_encoding orig_encoding
      content.encode! encoding
    end
    unless content.valid_encoding? then
      warn "unable to convert #{filename} to #{encoding}, skipping"
      content = nil
    end
  end
  content
rescue ArgumentError => e
  raise unless e.message =~ %runknown encoding name - (.*)/
  warn "unknown encoding name \"#{$1}\" for #{filename}, skipping"
  nil
rescue Encoding::UndefinedConversionError => e
  if force_transcode then
    content.force_encoding orig_encoding
    content.encode! encoding, :undef => :replace, :replace => '?'
    content
  else
    warn "unable to convert #{e.message} for #{filename}, skipping"
    nil
  end
rescue Errno::EISDIR, Errno::ENOENT
  nil
end
						Sets the encoding of string based on the magic comment
# File lib/rdoc/encoding.rb, line 71
def self.set_encoding string
  first_line = string[%r\A(?:#!.*\n)?.*\n/]
  name = case first_line
         when %r^<\?xml[^?]*encoding=(["'])(.*?)\11// then $2
         when %r\b(?:en)?coding[=:]\s*([^\s;]+)/   then $1
         else                                           return
         end
  string.sub! first_line, ''
  return unless Object.const_defined? :Encoding
  enc = Encoding.find name
  string.force_encoding enc if enc
end
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