[ruby-talk:8451] Re: string like istringstream (was: A bug inruby)

In article <[e-mail]>,
Kevin Smith  <[e-mail]> wrote:
>[e-mail] wrote:
>>point. But, since my last post, further thought has led me to a solution
>>(if you like it it can be in the  FAQ, Dave). The API from IO that I use
>>is just  for now .read  and .seek  but I may  want to use  other methods
>>eventually. The solution to share code is
>>
>> 1- Derive a class from String that  has methods .read and .seek . I say
>> derive a  class because  I need  to add  an instance  variable 'current
>> pointer' and it  seems cleaner to have  this in a new  class. But since
>> instance  variables can  magically appear  maybe  I need  not derive  a
>> class. I can just do:
>
>Perfect. And I agree that it should be a distinct 
>class. I would propose IOString as the name. 
>
>Perhaps we persuade you to contribute what you 
>end up with to the RAA (Ruby App Archive) so 
>others can benefit from it, and extend it.

Well, below is  my code. It is  a kind of 'minimal' solution:  I did not
derive a different  class from string, and  I did not even  add a method
as_file since .rewind  does the job. Also I have  yet implemented only a
small subset of the ID3V2 standard, but which covers all the music files
I have on  my hard disk. At  the bottom is a sample  application where I
run over all  .mp3 files in a  directory, show the ID3v1  and ID3v2 tags
and propose  to rename the  file to trak_no+title.mp3 (I  follow windows
filename conventions, I work under  windows with djgpp). Any comments on
how to shorten or rubify my code are welcome.

class String
  def rewind
    @current_pointer=0
  end
  def read(n)
    @current_pointer+=n
    if @current_pointer>=length
       @current_pointer=length
       nil
    else
      self[@current_pointer-n..@current_pointer-1]
    end
  end
  def seek(n,where)
    case where
      when IO::SEEK_CUR
         @current_pointer+=n
      when IO::SEEK_END
         @current_pointer=length+n
      when IO::SEEK_SET
         @current_pointer=n
    end
    0
  end
  def show
    gsub(/[\000-\037]/,sprintf('\\\\%03o',$0.to_i))
  end
end

class ID3V2tag
  attr_accessor(:size,:pad,:version,:revision,:flags,:frames)
  def to_s
    res="ID3V2."[e-mail]_s+"."[e-mail]_s
    @flags.each_byte { |fl,i|
       if fl==?1 
	res<<"["<<%w[Unsynchronisation Extended_Header Experimental_indicator
	  Footer_present Unknown4 Unknown5 Unknown6 Unknown7][i]<<"]"
       end}
    res+=" Size="[e-mail]_s+" Padding="+pad.to_s+"\n"
    res<<@frames.map{|x| x.to_s}.join("\n")
    res
  end
  def [](tag)
    @frames.detect{|f| f.header==tag}
  end
end

class ID3V2Frame
  attr_accessor(:header,:size,:flags,:data,:encoding)
  def to_s
    desc={"TRCK"=>"Track/Elts", "TMED"=>"Media Type", "TCON"=>"Content Type",
          "TALB"=>"Album Title", "TPE1" =>"Lead Artist", "TIT2"=>"Title",
	  "TYER"=>"Year", "COMM"=>"Comment", "TLEN"=>"Length", "TFLT"=>"Type"}
    desc.default="??"
    h="["+@header+"]"+desc[@header]
    e=case @encoding
      when 0 then ""  # ISO-8859-1 (default)
      when 1 then "[UTF-16]"
      when 2 then "[UTF-16BE]"
      when 3 then "[UTF-8]"
      else "[UNKNOWN]"
    end
    case @header
      when "COMM" 
        sprintf("%-20s<%s>",h+e+"["+@data[0..2].show+"]",@data[3..@size-2].show)
      when /T.../ then 
	res=sprintf("%-20s<%s>",h+e,@data.show)
	if @header=="TLEN" 
	  res+=sprintf("=%.3f sec.",@data.to_i/1000.0)
	elsif @header=="TFLT"
	  res+="="+{ "MPG"=>"MPEG_Audio", 
	  "/1"=>"MPEG_1/2_layerI", "/2"=>"MPEG_1/2_layerII",
	  "/3"=>"MPEG_1/2_layerIII", "/2.5"=>"MPEG_2.5",
	  "/AAC"=>"Advanced_audio_compression ",
	  "VQF"=>"Transform-domain_weighted_interleave_vector_quantisation",
	  "PCM"=>"Pulse_code_modulated_audio"}[@data]
	end
	res
      else h.ljust(20)+"<"[e-mail]+">"
    end
  end
end
    
module ReadID3tag
  def read_synchsafe_i
    res=0
    read(4).unpack("C4").each { |b| res=128*res+b}
    res
  end

  def read_frame
    res=ID3V2Frame.new
    res.header=read(4)
    if res.header[0]==0
      seek(-4,IO::SEEK_CUR)
      return nil
    end
    res.size=read_synchsafe_i
    res.flags=read(2).unpack("B8B8").join
    res.data=read(res.size)
    case res.header
      when /(T...)|(COMM)/ then res.encoding=res.data.slice!(0)
    end
    res
  end

  def read_ID3V2_tag
    rewind
    if read(3)!="ID3" then return nil end
    res=ID3V2tag.new
    res.version,res.revision,res.flags=read(3).unpack("CCB8")
    res.frames=[]
    res.pad=res.size=read_synchsafe_i
    while res.pad>=10 and (fr=read_frame)
      if res.pad<fr.size+10 then raise "Wrong Frame" end
      res.pad-=fr.size+10
      res.frames<<fr
    end
    read(res.pad).each_byte{|i| if i!=0 then raise "non null byte at end" end}
    return res
  end

  def read_ID3V1_tag
    seek(-128,IO::SEEK_END)
    tag,title,artist,album,year,comment,track,genre=
                         read(128).unpack("Z3Z30Z30Z30Z4Z28xC1C1")
    if tag!="TAG"
      nil
    else
      "ID3V1\nTitle=<"+title.show+">\nArtist=<"+artist.show+">\nAlbum=<"+
      album.show+">\nYear="+year.show+"\nComment=<"+comment.show+
	  ">\nTrack="+track.to_s+"\nGenre="+genre.to_s+"\n"
    end
  end
end

class IO
  include ReadID3tag
end

class String
  include ReadID3tag
end

Dir["*.mp3"].each{ |f| print "\n{",f,"}\n"
  tag=open(f,"rb"){ |fl| print fl.read_ID3V1_tag; fl.read_ID3V2_tag}
  print tag,"\n"
  if tr=tag["TRCK"] then
    newname=sprintf("%02d-%s.mp3",tr.data.to_i,tag["TIT2"].data.tr(
       " :`\"\\/*?|","_;''--#_-"))
    print "propose rename (y/n/q) to\n",newname
    case gets
      when "q\n" then break 
      when "n\n" then next
      when "y\n" then File.rename(f,newname)
      else raise "should answer q,n or y"
    end
  end
}