From: Joel VanderWerf <vjoel@...>
Date: 2007-05-25T05:51:08+09:00
Subject: Re: sending data, no strings via socket

Javier None wrote:
...
> data = 10
> socket = TCPSocket.new(home,port)
> socket.write(data)
> 
> on the other end I get
> receieved byte dump
> 0000: 31 30                10
> 
> which is the ascii for 10. How can I tell Ruby to send the 0x10?

IIRC, #write(arg) is converting arg to a string, so the number 10 is 
converted to the string "10", as you noticed.

If you construct the string yourself, you can control what binary data 
is in this string:

irb(main):029:0> data = "\012"
=> "\n"
irb(main):030:0> data[0]
=> 10

(note that \nnn uses octal).

But since it's hard to handle endianness and multibyte numbers this way, 
you probably want to use pack/unpack as Axel suggested.

If you want a friendly interface to do this, check out my bit-struct lib:

http://redshift.sourceforge.net/bit-struct/

For example:

---------------------------------
require 'bit-struct'

class MyData < BitStruct    # typedef struct{
   unsigned  :type,  32      #   u_int32_t type;
   unsigned  :len,   8       #   u_int8_t len;
   rest      :buf            #   u_int8_t * buf;
end                         # }

data = MyData.new
data.type = 1234
data.buf = "fred flintstone"
data.len = data.buf.length

p data       # ==> #<MyData type=1234, len=15, buf="fred flintstone">
p data.to_s  # ==> "\000\000\004\322\017fred flintstone"
---------------------------------

Note that the number format is big-endian (by default), which makes 
sense if you're writing network code.

Also note that the pointer is replaced with the buf bytes themselves, 
which is probably how you want it (you didn't really want to send a 
pointer over a tcp socket, right?).

-- 
        vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407