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From Tom Evans <tevans...@googlemail.com>
Subject Re: [users@httpd] accessing named pipe files from apache web server
Date Thu, 22 Mar 2012 15:03:31 GMT
On Thu, Mar 22, 2012 at 1:56 PM, Mysterious Mose
<webmaster@drdemento.com> wrote:
> Good morning,
>
> […]
>
>    Why is this so difficult, and why aren't more people interested in
> doing this? It seems like such a simple thing to do. If I create a
> named pipe and write data to it, cat can get the data out, along with
> many other programs. So why is apache different? Is it intentionally
> trying to avoid reading data from named pipes, or is there some
> low-level operating system issue that makes it difficult, which cat
> has no problem with because it's part of the shell?
>
>    Thank you for any insight!
>

I think you are thinking about this too simply. If you mkfifo a fifo,
and then write data to it, you aren't actually writing data, as there
are no readers of the fifo yet; the writing process is blocked waiting
for the fifo to become writeable.

Similarly, how should Apache deal with serving the fifo. Should it
open it for both read and writes, ie allowing multiple writes to the
fifo to appear in a single response, or should it open it just for
reads, and punt as soon as one write is received. What should it do
when there is no data to be read from the fifo?

As you said, all these things are trivial, so I suggest you knock up a
CGI that treats FIFOs as you want them to be treated and returns the
data/times out as appropriate.

Cheers

Tom

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