HTTP protocol with chunked transfer, persistent connection and reverse Ajax

Web QQ has been used, which involves the technology, there is a reverse Ajax.

Reverse Ajax is also called Comet,server push, server push technology.

Application: web chat server, Sina Weibo online chat, Google Mail web chat, all useful.

Principle: Generally speaking, the characteristics of HTTP protocol, connection <-> disconnection.

When is the specific time to disconnect?

The server responds Content-length, and when it receives the content of the specified length, it is disconnected.

In the http1.1 protocol, you are allowed to not write content-length, such as when the length of the content to be sent is really unknown.

At this point, a special content-type:chunked is required

<?phpset_time_limit (0); Ob_start (); $pad = Str_repeat (", 4000); Echo $pad, ' <br/> '; Ob_flush (); flush ();  Send the resulting content to the browser immediately instead of waiting for the script to end. $conn = mysql_connect (' localhost ', ' root ', ' 111111 '), mysql_query (' Use test ') and while (1) {    $sql = ' select * from msg where flag = 0 ';    $rs = mysql_query ($sql, $conn);    $row = Mysql_fetch_assoc ($rs);    if (!empty ($row)) {        echo $pad, ' <br/> ';        echo $row [' content '], ' <br/> ';        mysql_query (' Update msg set flag=1 ');    }    Ob_flush ();    Flush ();  Send the resulting content to the browser immediately instead of waiting for the script to end.    Sleep (1);} /* Read the contents of the database so that it can be achieved, instant communication. Server-Side---uninterrupted--push message--to client */

HTTP protocol with chunked transfer, persistent connection and reverse Ajax