From: James Gray <redmine@...>
Date: 2009-02-03T23:06:18+09:00
Subject: [ruby-core:21803] [Feature #908] Should be an easy way of reading N characters from am I/O stream

Issue #908 has been updated by James Gray.


I needed this in the standard CSV library.

My use case was that I peek ahead in the stream to determine what kind of line endings it has.  I just grab a block of characters and see if I find any standard line endings in there.  This was pretty challenging in Ruby 1.9, because just reading some bytes meant I had great chances to have picked up invalid data.  Then, when I hit it with a Regexp to find the line endings, an Exception is raised.

I'm using this code to get around that problem in CSV:

  # 
  # Reads at least +bytes+ from <tt>@io</tt>, but will read up 10 bytes ahead if
  # needed to ensure the data read is valid in the ecoding of that data.  This
  # should ensure that it is safe to use regular expressions on the read data,
  # unless it is actually a broken encoding.  The read data will be returned in
  # <tt>@encoding</tt>.
  # 
  def read_to_char(bytes)
    return "" if @io.eof?
    data = @io.read(bytes)
    begin
      encoded = encode_str(data)
      raise unless encoded.valid_encoding?
      return encoded
    rescue  # encoding error or my invalid data raise
      if @io.eof? or data.size >= bytes + 10
        return data
      else
        data += @io.read(1) until data.valid_encoding? or
                                  @io.eof?             or
                                  data.size >= bytes + 10
        retry
      end
    end
  end

That worked for CSV, where I just need some characters and don't have to have an exact count.  If you do need an exact count though, the code gets more complicated.

I agree that this is something Ruby should do for us.

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