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Re: ncat usage
From: Dave Henderson <dhenderson () digital-pipe com>
Date: Mon, 14 May 2012 08:56:58 -0400

On 05/11/2012 11:36 AM, Dave Henderson wrote:
On 05/11/2012 11:10 AM, David Fifield wrote:
On Fri, May 11, 2012 at 07:03:31AM -0400, James Rogers wrote:
OK, you can only use ncat to serve a single page at a time to one web
browser, using ncat on the command line like you are. Which means you
cannot embed any images from that same server in the page you are
serving.  Because every image is a separate connection.

The reason for this is that every connection in to ncat would need
it's own separate handles for each send and receive, but you just have
two handles, so everything you send goes into the stream for the first
client that connects and nothing is ever sent to the second
simultaneous connection.

This is why the image shows up in the middle of your first web page as
text.  If 5 clients connected simultaneously the first connection
would get 5 pages randomly mixed together.

There might be a way using nse scripting to make ncat work like a full
featured web server, but at that point I would recommend just using a
small web server like boa or lighthttp.
Also I should mention that anything you do in this case that does not
involve --exec or --sh-exec is the wrong answer. What you are trying to
do--handle multiple clients independently--is exactly what those options
are for. Putting a while loop around a single invocation of Ncat reading
from stdin is wrong for a number of reasons, including the one James
just mentioned.

If you need to support getting different URLs, then it's up to you to
write a small program capable of parsing the URL from the HTTP stream
and responding appropriately. Just sending back a block of HTTP
responses without even looking at requests is not robust or correct.
Instead of reinventing a minimal web server, why don't you use something
likehttp://www.acme.com/software/mini_httpd/?

David Fifield

Thanks for the help David! I looked over the man pages for those two parameters and have a few questions.

1. Should one of those parameters be used instead of, or in conjunction with, the named pipes?

2. Would it be possible to provide example syntax to use based on the code already provided?

3. I can see that --sh-exec uses /bin/sh to run the command, what does --exec use (I assume whatever the shebang is)?

I have to mention, as I did in one of the prior replies, that this project is _not_ for handling multiple clients. It's a single instance of a server, serving one person. There are other aspects (and flexibility) of the project that would make it better to use the script I'm working on instead of other servers such as boa, lighttpd, mini_httpd, or other web servers.

I have tried using ncat in the 'while' loop (restarting each iteration) as well as a 'keep-open' connect outside of the 'while' loop. In both instances, the connection does not close (which I'm assuming is because I wasn't using an --exec or --sh-exec parameter). It's not the number of named pipes (given the scenario), it's that they don't get closed once the entire data has been sent. This explains why the headers and raw contents of the graphics file get added as part of the HTML. If the original connection closed after sending the .html file contents, ncat (and it's associated named pipes) would be free to serve the request from the browser for the graphic file contents and any other "embedded" documents that would need to be sent in order to render the page correctly.

Also, part of the script (the procRequest function call), not provided in any messages so far, actually parses and handles the URI request, so that part is handled and will be expanded as needed. Thanks for the tip though. :)

Dave



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