From: Joel VanderWerf <vjoel@...>
Date: 2006-11-17T09:52:32+09:00
Subject: Re: Another IO.popen question ...

ara.t.howard@noaa.gov wrote:
> On Fri, 17 Nov 2006, Joel VanderWerf wrote:
> 
>> Adam Groves wrote:
>>> Hi Joel,
>>>
>>> thanks for the speedy reply! The problem is, I need to pass on a file 
>>> object (which has been uploaded from a web page form) to 'convert' 
>>> and not just a path. I should have made this clearer in my original 
>>> post.
>>>
>>> Any ideas?
>>>
>>
>> Untested, but maybe something like this?
>>
>> file = File.open("mypdf.pdf")
>> IO.popen("convert -resize 700x700 pdf:-[0] png:-") do |f|
>>  while (data=file.read(N))
>>    f.write data
>>  end
>> end
> 
> careful, if you don't read the child will block when the pipe becomes 
> full i
> think.  you might need to add
> 
>   file = File.open("mypdf.pdf")
> 
>   png =
>     IO.popen("convert -resize 700x700 pdf:-[0] png:-") do |f|
>       while (data=file.read(N))
>         f.write data
>       end
>       f.close_write
>       f.read
>     end
> 
> not sure if that was obvious or not...  sorry if it was.

I was confused in several respects: I was thinking of a one-way pipe 
(but I forgot the "w"), in which case blocking wouldn't be a problem. 
But the one-way pipe would only be useful if the OP could put a filename 
in place of the "png:-".

The one-way pipe has the advantage that you can read(N) instead of 
read(), and keep memory bounded. Maybe it's not an issues for the OP, 
though.

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