|
"100+ Auto-Installing Software Titles For Your Web Site"
|
07-05-2001
by John Saya
Did you ever want to output information in realtime, such as making a chat room, or displaying data as the server processes it -- like credit cards, searching, or? Well, with most web servers it is possible, and relatively simple to do using Perl. It's called server pushing or streaming.
It's all done by sending the multipart/mixed header instead of using the standard text/html header when sending text from your Perl script. The text/html header generally only displays information when all of the data is sent from the server, and the server closes the connection with the browser. The multipart/mixed keeps a live connection open with the server and displays all data on the visitor's browser as it is output by the server. However, be careful when doing this as you could cause your server to become extremely slow or crash due to low memory or system resources.
The first thing you should know is that many Windows based web servers do not support this header, so it will act the same as text/html. But, give it a shot any way, because by the time you read this, your web server may support it.
The next step is crucial in having a realtime stream. It's called buffering. Basically Perl will buffer all data until the buffer is full, before any data is actually sent to tge browser. So, you turn off buffering in your script by using:
Another thing to keep in mind is that Microsoft Internet Explorer and Netscape Communicator require slightly different methods of accomplishing a realtime data stream. So, we will add a browser check routine and call it in the beginning of the script:
To call the above routine, just use:
Now when you want to output, first use this:
The boundary portion really doesn't apply to this process, but I use it anyway for older browser compatibility. Remember that you only need to send the above header one time in your script. Once it's sent, a live connection is open between the server and the browser until the script exits or the visitor closes their browser.
The next step is optional, but you may want to output a few lines of hidden comments to ensure the browser is beginning the stream. Some browsers buffer their own data and won't stream until that buffer is full:
Now you can output text in realtime. For testing purposes, you can display ten lines of text in one second intervals:
Be sure to use the newline character (\n) because some Netscape browsers will not output the text until the newline is detected.
Your entire Perl script should look like this:
You should now have a basic understanding of how to stream data in realtime to a visitor's browser. If you want to see a more sophisticated method of streaming, check out WebChatter at the CGI Connection. Happy streaming!
[ Back ] [ Main Menu ]
Download Fuse Node.js Compiler
by John Saya
Did you ever want to output information in realtime, such as making a chat room, or displaying data as the server processes it -- like credit cards, searching, or? Well, with most web servers it is possible, and relatively simple to do using Perl. It's called server pushing or streaming.
It's all done by sending the multipart/mixed header instead of using the standard text/html header when sending text from your Perl script. The text/html header generally only displays information when all of the data is sent from the server, and the server closes the connection with the browser. The multipart/mixed keeps a live connection open with the server and displays all data on the visitor's browser as it is output by the server. However, be careful when doing this as you could cause your server to become extremely slow or crash due to low memory or system resources.
The first thing you should know is that many Windows based web servers do not support this header, so it will act the same as text/html. But, give it a shot any way, because by the time you read this, your web server may support it.
The next step is crucial in having a realtime stream. It's called buffering. Basically Perl will buffer all data until the buffer is full, before any data is actually sent to tge browser. So, you turn off buffering in your script by using:
$| = 1;
Another thing to keep in mind is that Microsoft Internet Explorer and Netscape Communicator require slightly different methods of accomplishing a realtime data stream. So, we will add a browser check routine and call it in the beginning of the script:
sub check_browser
{
$browser = 0; #MSIE / AOL
if ($ENV{'HTTP_USER_AGENT'} =~ /Mozilla/i)
{
if ($ENV{'HTTP_USER_AGENT'} !~ /MSIE/i and $ENV{'HTTP_USER_AGENT'} !~ /opera/i)
{
$browser = 1; #Netscape
}
}
}
To call the above routine, just use:
&check_browser;
Now when you want to output, first use this:
print "Content-type: multipart/mixed;boundary=\"boundary\"\n\n";
if ($browser == 1)
{
print "\n--boundary\n";
print "Content-type: text/html\n\n";
}
The boundary portion really doesn't apply to this process, but I use it anyway for older browser compatibility. Remember that you only need to send the above header one time in your script. Once it's sent, a live connection is open between the server and the browser until the script exits or the visitor closes their browser.
The next step is optional, but you may want to output a few lines of hidden comments to ensure the browser is beginning the stream. Some browsers buffer their own data and won't stream until that buffer is full:
for ($x = 0; $x < 50; $x++)
{
print "<!-- FORCE STREAM -->\n";
}
Now you can output text in realtime. For testing purposes, you can display ten lines of text in one second intervals:
for ($x = 0; $x < 10; $x++)
{
print "Line $x<BR>\n";
sleep 1;
}
Be sure to use the newline character (\n) because some Netscape browsers will not output the text until the newline is detected.
Your entire Perl script should look like this:
#!/usr/bin/perl
$| = 1;
&check_browser;
print "Content-type: multipart/mixed;boundary=\"boundary\"\n\n";
if ($browser == 1)
{
print "\n--boundary\n";
print "Content-type: text/html\n\n";
}
for ($x = 0; $x < 50; $x++)
{
print "<!-- FORCE STREAM -->\n";
}
for ($x = 0; $x < 10; $x++)
{
print "Line $x<BR>\n";
sleep 1;
}
exit;
sub check_browser
{
$browser = 0; #MSIE / AOL
if ($ENV{'HTTP_USER_AGENT'} =~ /Mozilla/i)
{
if ($ENV{'HTTP_USER_AGENT'} !~ /MSIE/i and $ENV{'HTTP_USER_AGENT'} !~ /opera/i)
{
$browser = 1; #Netscape
}
}
}
You should now have a basic understanding of how to stream data in realtime to a visitor's browser. If you want to see a more sophisticated method of streaming, check out WebChatter at the CGI Connection. Happy streaming!