From: Robert Klemme <bob.news@...>
Date: 2006-02-28T18:08:38+09:00
Subject: Re: Sending Binary Data?

Yacin Nadji wrote:
> Hello Ruby Gurus!
>
> My friend and I are writing a chat/IM client in Ruby. It's nothing
> special, but it's helping us learn the language, especially the lower
> level networking parts really well and I'm thoroughly enjoying the
> project so far. I thought implementing file transfers would be pretty
> nifty, but I'm running into some problems. I did a simple copy by
> reading the file (a picture) and adding the lines to a string, and
> writing that string out to a new file:
>
> a = String.new
>
> IO.foreach("lighter.jpg") do |line|
>   a += line
> end

This approach is quite inefficient in two ways:

 - you use + for string concatenation which constantly creates new objects
and throws old ones away.  Better use <<

 - You need to keep the whole file in mem while with a streaming approach
(reading and writing a chunk at a time only) you can deal with arbitrary
sized files without worrying about memory.

> file = File.open("new.jpg","w")

You should use mode "wb" - even if on Linux.

> file.write(a)
> file.close
>
> And it worked swimmingly, however, when I tried to do this over a
> TCPClient/Server:
>
> server.rb
>
> require 'socket'
> port = 9191
> file = File.open("omgnew.jpg","w+")

"wb" again...

> server = TCPServer.new('localhost', port)
> while session = server.accept
>   file.write(session.gets)

Better use #read and #write instead of gets!

>   server.close
>   file.close
> end
>
> client.rb
>
> require 'socket'
>
> server = TCPSocket.new('localhost',9191)

You want TCPServer here.

> file = String.new
> IO.foreach("lighter.jpg") do |line|
>   file += line.chomp
> end

# untested
srv = TCPServer.new('localhost',9191)

while ( sess = srv.accept )
  Thread.new(sess) do |session|
   File.open("lighter.jpg", "rb") |io|
     session.write(io.read(1024))
   end
  end
end

> server.send(file,0)
>
>
> It works for a bit, then I get this error:
>
> server.rb:7:in `accept': closed stream (IOError)
>         from server.rb:7
>
> The file sizes are nearly identical, I'm off by 479 bytes:
>
> ynadji@onizuka:file_transfer$ du -b *
> 122753  lighter.jpg
> 122274  omgnew.jpg
>
> Any ideas? I could be doing this entirely wrong, searching didn't
> yield any helpful results, so I figured I'd turn here. I was reading
> around with Array#pack and String#unpack which seems to be heading in
> the right direction, but I'm completely lost :P.

Hope I could give some valuable hints.

Kind regards

    robert