Re: Re: Re: [PHP] Full-Duplex communication

Thanks for the reply Miguel, but here i'm not trying to implement my own multi-threaded server - exactly the reason why i'm using Apache / PHP. I could have made a listening server which is based on a multi-threaded or multi-forked model, but the time and complexities involved would be huge. Thats why I chose Apache / PHP. Now if what i'm asking for can be done, developers can easily leverage existing efficient server technologies (Apache) to build their own App servers. I know that there is no existing function in PHP that would allow it to retrieve the socket from Apache ;), all i'm asking for is a hack that would allow me to do it. I thought that i'd just as well post it on the mailing list before diving into the source code and trying to figure out for myself. No point trying to re-invent the wheel, right? Evan, that lib will allow me to create my own packets, but which socket do i send it to? Thats been the question all along. I think this is getting really interesting :) Tx, Vinod. On Wed, 22 May 2002 Miguel Cruz wrote :

I don't think you're going to get Apache to hand you the socket. However, you can write a program using the standalone (CGI) PHP interpreter that will act like a server - check out http://php.net/socket_create_listen for more info. You could redirect from your standard web server to your listening PHP app running on another port. You'll then have to implement at least a subset of the HTTP protocol in order to get browsers to talk to you. Unfortunately, since you can't - to the best of my knowledge - fork a PHP program, you're going to have to do your own homebrew threading which will make life slightly complicated. miguel On 22 May 2002, Vinod Panicker wrote: It still seems like I havent made the problem clear enough. I am aware of the print(), echo() and flush() functions and what they do. It does not fit in as a solution. Let me explain my problem more elaborately - The client calls a PHP script, script_a.php on the Apache web server, using a Keep-Alive connection. The script returns some response to the client which it uses. Now since the connection is a Keep-alive, apache still has it open for reading and writing. When the client wants to call other scripts, it just sends the request over the same connection. Now the thing is that if the server needs to send some ASYNCHRONOUS data to the client, without the client requesting for anything, a normal PHP script wont be able to do it, since the script would get executed by the web server ONLY on a client request (coz thats the way HTTP works). Now what i was thinking was - if i could get hold of the socket that is being used by apache to send data to the client, I could effectively write() to it, from a C++ app or a PHP script (which gets invoked from lets say another server). print(), echo() etc are functions that write to the output stream, which is opened as a result of the clients request, by the web server. I want the ability to write to a socket thats been created earlier - i want to steal it from Apache, so that i can use it when and where i like. Functions like echo() and print() are not going to work here, i will have to use write() so that i can specify the socket to which the data has to be written! Hope the problem is understood now. Now for your question - When the client wants to send data to the server, it just has to open a socket connection with the web server, and issue a GET or a POST request! if the connection is a keep-alive connection, and it has already been created, the client just has to do a GET or a POST without the need to connect(). This mechanism, where the client frequently connects() to the server and checks for messages is called polling. One way of reducing the high overhead of this is to reuse the connection by using a keep-alive connection. A still better improvement would be to remove the need for a poll altogether, by doing something (thats what my question is all about) on the server so that it can send data asynchronously to the server. Tx, Vinod. On Wed, 22 May 2002 Bogdan Stancescu wrote :

For your specific problem, I think Mr. Lemos has provided a viable solution (using print() or echo() and flush() whenever

you

need to, instead of grabbing the socket and write() to it).

My

problem however is how you envision solving the communication

the

other way around (i.e. when the CLIENT wants to send data to

the

server). Bogdan Vinod Panicker wrote:

Hi, Tx for your very prompt reply. Yeah, I'll post the solution as soon as I find it

someplace.

Let me outline the problem in more detail - Client (VC++) calls a PHP script on the server, specifies

the

connection type as Keep-Alive. The PHP script, somehow

(still a

big question) gets the socket on which the apache server

has

received the client request (so that it can send data to

the

client later) and stores it in a database. Now whenever another PHP script wants to send data asynchronously to the client, it gets the socket from the database, and just calls a write() on it. Since the

connection

is still open (Keep-Alive), the client receives the

information,

and doesnt have to poll the server periodically. The application of this is indeed destined for a messaging product, and could benefit a lot of other areas as well. The only thing that is needed is the socket from apache. Someone somewhere knows how to get this done, i'm sure :) Possibly a hack into the PHP module can get this done, i'm

open

to suggestions. Tx, Vinod. On Tue, 21 May 2002 Bogdan Stancescu wrote :

Hi! I'm looking for an answer to your questions as well, so if

you

do find a solution on other lists, could you please post

it

here as well? Regarding the issue, your proposal wouldn't make for full-duplex as far as I understand since I don't see how

the

client would be able to send any data on the same

connection

_after_ getting connected. What are you using on the other end of the pipe (on the client)? Plain HTML? Flash? Java? Something else? Bogdan Vinod Panicker wrote:

Hi, We have developed a client-server application where the

server

needs to send asynchronous data to the client. Now since

we

are using Apache/PHP/MySQL, the client needs to poll the server periodically for information. I was thinking if there was some way to get around this

basic

problem. I understand that this is how things are

supposed to

work, but it would be just great if i could PUSH data from

the

server to the client, using HTTP. Since HTTP is a request/response based protocol, Apache

would

not send any data to the client asynchronously. So what i

was

thinking was - If i tell the server to allow Keep-Alive connections, and increase the timeout value and max

requests,

I would effectively have a constant TCP connection. Now

the

only problem would be of sending asynchronous data to

the

client. Solution? Here goes - If there was some way in

which

i could get hold of the file descriptor(socket) that is

being

used by apache to write data to the client, then i could,

from

a PHP script also send any data to the client using the

socket

functions of PHP since i already have the socket with

me.

This would mean that the client doesnt have to poll the

server

for data any more... and if the connection does get

closed,

the client could reconnect to the server asking for

another

keep-alive connection. Now I know that this is probably the wrong place to put

such a

query - maybe the apache list would have been better.

But

since I'm using PHP out here, i thought i'd give it a

try.

Does the solution sound very outlandish? Are there any pitfalls? And finally, how do i get hold of the socket?

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