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Server push allows a server to send continual updates of a document or image. Server push can be implemented with custom scripts or with the ".holopush" extension.

This feature is available for both standard and demo HoloWWW service.

For more information, see also:

• Netscape: An exploration of dynamic documents

For the most part, animated .gif images have superceded the use of server push, but whereas animated .gifs are static files, server push scripts can be customized to provide greater flexibility.

Example

This is a script file called "sample.holopush":

Not Found
The requested URL /htbin/holopush/support/holowww/sample.holopush was not found on this server.


Apache/1.3.22 Server at www.holonet.net Port 80

Example HTML

<IMG SRC="sample.holopush" WIDTH=468 HEIGHT=60 ALT="[SAMPLE]">

Example Parsed HTML

If your browser supports Server Push, the above image would change randomly every 3 seconds.

HoloPush Instructions

# comment

HoloPush ignores lines starting with a "#".

dec variable

Subtracts one from the variable.

delay seconds

Delay by seconds. Partial seconds can be specified with a decimal point.

end

HoloPush closes the connection and stops.

goto labelname

Execution continues at the named label

goto-random odds1:labelname1 .. oddsN:labelnameN

Jumps to a label at random. The odds of a labelnameX being choosen is oddsX out of the total odds.

if variable labelname

If variable is non-zero then exection continues at labelname.

ifnot variable labelname

If variable is zero then exection continues at labelname.

inc variable

Adds one to the variable.

label labelname

Names the current line labelname. See also: goto, if, and random.

multipart

Notify HoloPush that multiple graphics will be sent. If more than one graphic will be sent, this command is required before the first is sent.

send filename

File name is relative to the .holopush file. Variables can be placed in file names by enclosing them in braces. For example: 'sendfile "image{count}.gif"'.

send-random odds1:file1 .. oddsN:fileN

Sends a file at random. The odds of a fileX being choosen is oddsX out of the total odds. File name is relative to the .holopush file. Variables can be placed in file names by enclosing them in braces. For example: 'sendfile "image{count}.gif"'.

serverpush

This is a pre-set variable. If HoloPush believes the browser supports server push then this variable is set to 1. Otherwise, it is 0.

set variable=number

Set a variable to number. Variable names must begin with a letter and contain only letters, digits, underscores, and dashes. number must be an integer.

Technical Notes

• To prevent abuse by non-HoloWWW customers, HoloPush requires that the calling browser provide a REFERER of one of your Web pages.

• HoloPush does not send the same file twice in a row, the send command is skipped.

• HoloPush ignores blank lines in .holopush files.

• To disable server push, you can set the serverpush variable as follows:

      set serverpush=0
  

  You might want to do this in order to test how your script would be viewed on a browser which does not support server push.