Re: HELP: send binary replies back and forth ???

You're right. my MD satellite device can not support those advanced features
(actually is a GPRS device), but security on that side is not an issue. It's
a client, not a server. And I will use MD5 (and I don't mean Mystery Device
5 here :)) for minimal but fairly robust way to verify data integrity with a
secret password as part of the soup that MD5 is applied on.

Anyway, forget about all that... It does look like I won't be able to use
apache (even though the timeout won't be an issue.. and yes, you can use a
simple php function to set the timeout), .. but there's no reason not to use
php instead of perl/java.

I know you can write whole webservers in php (see nanoweb
http://nanoweb.si.kz/) but I need something more simple.

Issues in writing php server are:
- chroot / run under certain user privileges that would disallow someone to
execute shell commands.
- ensure certain number of concurrent connections but not make it vulnerable
to DOS attacks.
- server start/stop scripts

Lisa

"Erwin Moller"
<since_humans_read_this_I_am_spammed_too_much@xxxxxxxxxxxxxxxx> wrote in
message news:43032940$0$11066$e4fe514c@xxxxxxxxxxxxxxxxx
> Lisa Pearlson wrote:
>
>> Hi,
>>
>> My php application (on Apache/Linux) needs to do the following:
>>
>> The PHP script receives a request from a client (binary), asking for
>> certain records of data.
>> My PHP script loops through all records and sends each of them ONE BY
>> ONE.
>> After each record that my server script sends, it waits for the client to
>> confirm proper reception with an ACK (binary digit).
>> When there are no more records, my server script sends the client a
>> binary
>> digit 0.
>>
>> So the client initiates a connection to the webserver with my php script,
>> and communication then goes back and forth between the server and client
>> a
>> couple of times before a 'session' completes.
>> Looks like this:
>>
>> 1. client ---> server (client asks for records)
>> 2. client <--- server (server sends record 1)
>> 3. client ---> server (client confirms with ACK)
>> 4. client <--- server (server sends record 2)
>> 5. client ---> server (client confirms with ACK)
>> 6. client <--- server (server sends ACK to notify end of records)
>>
>> Additional info:
>> 1. The client is not a webbrowser but a piece of simple hardware that can
>> only do simple TCP/IP connections and doesn't come with any specific
>> internet application protocol such as HTTP. HTTP is easy enough to
>> implement just to exchange binary data, but there's no reason to use HTTP
>> other than to be able to communicate with apache.
>> 2. The reason I have to send records one by one is because the client is
>> a
>> special device with limited read buffer.
>> 3. All communication is binary because the connection used is pricy and
>> charged by kilobytes of data.
>>
>> Questions:
>>
>> 1. A webserver usually doesn't communicate back and forth, rather client
>> sends request, server sends reply, and connection is closed. Also, HTTP
>> headers generate extra overhead that I really don't need and want
>> (generates extra data that we get charged for). How can I accomplish
>> communication like the above with apache and php?
>>
>> I'm afraid I may have to write my own PHP style socket server without the
>> use of apache at all. Then it wouldn't have to be HTTP but all binary
>> communication only. The problem with this is that I think it might be
>> hard
>> to develop something robust in just 2 days. A webserver has a proven
>> track
>> record, has security features (think of DOS attacks) and other things
>> that
>> would be hard to implement myself. But all my script would need to do is
>> the above so it doesn't really need much.
>> I don't know how hard it would be to develop a php server that would
>> handle concurrent connections and keep running, and is secure enough that
>> it woudn't allow DOS attacks or worse, allow execution of commands on the
>> linux machine with root privileges. chrooting and other things is
>> something I'm not experienced enough with to trust. So I'd like to hide
>> behind apache if possible. But communicating binary data without HTTP
>> headers has proven impossible from within apache.
>>
>> Also, how can my script RESPOND in binary data?
>> "echo 0" doesn't send the byte value 0, rather the ascii value "0".
>> passthru allows binary data to be outputted but only in response to some
>> shell command.
>> And I guess "echo pack("C", 0)" wouldn't do it either.
>>
>> If the client could also act as a server, then I could've simply opened
>> up
>> a socket in response to the server and communicated back and forth with
>> it
>> in a loop, in a single call via apache.
>>
>>
>> Example quasi code that illustrates what I'd like to be able to do.
>>
>> server.php:
>>
>> $binary = $GLOBALS['HTTP_RAW_POST_DATA'];
>> $size = strlen($binary);
>> $arr = unpack( .... , $binary);
>>
>> if ($arr['request-type'] == 5) {
>>
>> $records = getBinaryRecords();
>> foreach($records as $rec) {
>> sendBinary($rec);
>> while (awaitReply() != ACK) {
>> sendBinary($rec);
>> }
>> }
>> sendBinary(ACK); // done
>> }
>
>
> Hi,
>
> I think your proposed setup will run into trouble.
> You make a loop that should wait for a response from your mysterydevice
> (Let's call it MD from now :-).
> PHP typically responds to 1 request.
> PHP also has a default 'scripttimeout' of 30(?) seconds, but that can
> probably be modified by you via php.ini.
>
> I think creating a session makes more sense, but that can prove difficult
> because your MD probably doesn't support http and cookies *I think*.
>
> Personally I would opt for a solution without PHP.
> Perl and Java might be much more suitable for your situation.
>
> About the 'hiding behind apache' for security: Yes, afaik apache is
> rocksolid (as long as you don't use obscure modules), but is you MD?
> Will your MD have a fixed IP-adres?
> If so, you can easily confige Java/Perl/PHP to only communicate with that
> IP.
>
> You probably need some authentication too.
> I guess you do not want some freak sending data to your MD.
> If you can, use SSH2 or something, but I do not know if that will give you
> a
> lot of extra datatraffic.
>
> Just my 2 cents.
>
> Regards,
> Erwin Moller
>
> PS: Just curious: Are you building a sattelite? :P


.

Relevant Pages

  • RE: MessageSecurityException when consuming WCF service
    ... a WCF based client server communication application, ... Microsoft MSDN Online Support Lead ...
    (microsoft.public.dotnet.languages.csharp)
  • Re: How do we get there from here?
    ... >> executing on the server as a pre-processor. ... If there are client side versions of PHP, ... > name implies a static text file, is it different from a PHP script? ...
    (comp.databases.pick)
  • Re: Which Is The Better Approach To Working With Javascript?
    ... However this is achieved, PHP has no script interface, ... Javascript is run **ONLY** on the client. ... but I think the original answers based on the level of the OP were probably good ones; run it client side because the server likely doesn't provide it?. ...
    (comp.lang.php)
  • Re: Looking For Code Sample and Request Feedback
    ... I would prefer to use a Windows Service but a web service will do to. ... What is very easy to do on a Server 2003 and with VBNet? ... > I am looking for a code sample that communicates from a client to a remote> Windows Service on another computer over the internet, that is the Windows> Service performing instructions the client sends. ... the client does the office automation and the actual> communication of the commands to this server. ...
    (microsoft.public.dotnet.languages.vb)
  • Re: How to check UID of process on the other side of local TCP/UDP connection
    ... Both client and server are on the same local host. ... the problem is that it requires some additional communication between ... Unix sockets (unless of course Unix sockets are the only good way to ...
    (Focus-Linux)