From: draygen@...
Date: 2009-01-30T06:23:35+09:00
Subject: Reading a file in chunks, to a byte array

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Hi everyone, 

I'm pretty new to Ruby, I'm taking courses and reading as much info as I can, but I'm stuck on this one problem that may/may not have a simple answer. 

A quick summary of what I'm trying to accomplish: 

I've written a simple SOAP client that interfaces with a web app used for file transfer... It works great, however, if a file is over a certain size it just hangs - and I know the reason why... 
The webapp receives the file as a chunk, in the form of a byte array, the great thing about Ruby is that strings are basically an arrangement of arbitrary bytes, so I can just pass a string with the file object into the web service and upload small files. 

But I'd like to split a file into "chunks" .. I know that I can do this: 

--- 

def get_chunk(bytearray) 
bytearray.read(61440) #read a 60kb chunk of the byte array 
end 

localFile = File.open('test.dat') 

get_chunk(localFile) 

--- 

But I need to keep track of more information .. The web app is looking for an offset integer , which basically works like this: 

(with a 60k chunksize) 

the first request will be: 
offset = 0 

second request: 
offset = 61440 

third request: 
offset = 122880 

Does anyone know how I could iterate over a bytearray, keeping track of the offset, and read 60k chunks all at the same time? 
in pseudo code: 

get_chunk(bytearray) 

bytearray.read(61440) 
offset = 0 
puts bytearray.pos 
=> 61440 

bytearray.read(61440) 
offset += 61440 
puts offset 
=> 61440 
puts bytearray.pos 
=> 122880 
.... 

After I have the proper offset, and chunks of a bytearray - I need to keep calling the web service method with that data until the file = eof. 

I'm horrible at code blocks and iteration, if anyone has any suggestions, it would be greatly appreciated. 

Thanks, 

Brian 




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