Create bytebuffer like object in Ruby

Question

I need to create a Bytebuffer like object in Ruby. Here is my example in JAVA

int ADD_BYTES_FOR_MSG_LENGTH = 4;

Integer messageBodySize = new Integer(messageBody.getBytes().length);
byte[] messageHeader = ByteBuffer.allocate(ADD_BYTES_FOR_MSG_LENGTH).putInt(messageBodySize).array();

messageToSend = new byte[messageHeader.length + messageBodySize];

System.arraycopy(messageHeader, 0, messageToSend, 0, messageHeader.length);
System.arraycopy(messageBody.getBytes(), 0, messageToSend, messageHeader.length, messageBodySize);

I create a message starting with 4 bytes where is located size of the message body part, and then the actual message. I have no idea how to do this in Ruby, so please help.

Koraktor · Accepted Answer · 2011-08-23 19:58:34Z

4

I did this for Steam Condenser using an extended version of StringIO.

Although I don't use any put* methods, these could be easily implemented like for example:

class StringIO

  def put_int(i)
    write [i].pack('v')
  end

end

You may have a look at the code, the documentation of the original class and my extensions.

edited Aug 23, 2011 at 19:58

answered Aug 23, 2011 at 8:44

Koraktor

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6 Comments

Mladen Jablanović Over a year ago

I guess you should use write instead of puts there?

Neuro Over a year ago

Thanks for help, but now I'm stuck again... when I do write [i].pack('L') (unsigned 32 bit integer) the StringIO object is allocating 5 bytes (method size is returning 5). I need to write this int on 4 bytes only (like in my java example). Could you give me a hint how to handle it?

mu is too short Over a year ago

@Neuro: Are you using write or puts? puts will append a newline and give you an extra byte, write won't. There's also syswrite which might match your desired semantics better.

Neuro Over a year ago

Yes! Stupid me. Classic copy-paste error. But unfortunately something is not working :/ I do put_int(size_of_msg) and then write(msg) on the StringIO object and I send it through the socket but in java side app I don't get expected message :/

Neuro Over a year ago

I got it! I did it by write [i].pack('N') for unpack in network byte order :) And i wrote to the socket by stringioobj.string method. Many thanks for all of you for help, this problem was pain in my ass for almost a week :)

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