From: Jamey Cribbs <jcribbs@...>
Date: 2006-11-28T00:06:39+09:00
Subject: Re: Appending to file in arbitrary position

Tulsi Das wrote:
> Hi, I'm implementing the server side of a file upload with resume option
> part of a web app.
>
> The client sends the last position so I have to append to the existing
> file from that position.
>
> Current code is:
>
> @uploadfile = @params["uploadfile"]
> content_range = @request.env['HTTP_CONTENT_RANGE']
> filename = @uploadfile.original_filename
> data = @uploadfile.read
>
> # position to append from
> pos = content_range[/\d+/].to_i
>
> f = File.open("#{filename}", "a")
> #f.pos = pos
> f.seek(pos)
> f.write(data)
> f.close
>
> I've tried opening the file with a and a+ modes. I've tried doing
> rewing, setting pos (like the commented line) and seek, and none of them
> works, the new data is always appended at the end of the file.
>   

Open the file in r+ mode.  This is read-write mode that starts at the 
beginning of the file and allows you to seek to a specific position.

Jamey