Re: Full-duplex communication

On Wed, May 22, 2002 at 10:16:23AM -0000, Vinod Panicker wrote: > The client calls a script on the server - script_a.php using a > keep-alive connection. The script gets the socket from the web > server (this is the unknown), and stores it in a database. Script > finishes execution, client reads response, but apache doesnt close > the connection since its keep-alive. > > Client wants to call another script on the server, just writes to > the same socket. Script returns response. > > Server wants to send data asynchronously to the client, so a PHP > script (invoked from another server) gets the socket of the client > from the database and writes to it. Client reads from the > socket. > > So this is basically a full-duplex connection over HTTP :) Not quite! Keep-alive tries to keep a socket connection with the server, but this connection can only be used to request several resources from the servers (like the images inside a page). This because setting up a new tcp-connection takes a lot of time, keep-alive just reuse this connection for another request. The server itself cannot *start* sending data over the http connection, it can only reply on a client request. What you can do however, is to create a script with an endless loop, inside this loop the scripts looks if there's new data in a database and if there's data, it's sent to the client.. You can ofcourse also do other things inside the loop. But you won't need a keep-alive connection for this. Ohh, don't use any out buffering, otherwise the browser will timeout after 30 seconds.. ;-) However the server can't switch pages. What you can do, is inside the loop to access a different page with the fopen function. Hope this will answer your question, -- With best regards, Dave Mertens, Development Manager dmertens@ism.nl Innovative Solutions in Media BV Schiekade 101 3033 BG Rotterdam, Netherlands Tel. +31-10-2436060 Fax. +31-10-2436066