Comet Reverse Ajax

One: HTTP protocol with technology-long link + chunked transfer----> Reverse Ajax

Reverse Ajax is also known as comet, Server push, and servers 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

The principle of split-field transmission is this:

123H \ r \ n

123H length of content transmission to the client ... \ r \ n

.......

41h\r\n

The browser continues to receive 41H-length content. \ r \ n

0\r\n (server says content is finished)

Combine with MySQL

<?php

Set_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 ');

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);
}

Comet Reverse Ajax