How To Write a perl cgi script which keeps on flus

问题:

Possible Duplicate:
Reg: Perl CGI script Autoupdate with New Data

A perl CGI script continuosly updating the time, instead of creating a time list

#!C:/perl/bin/perl.exe
use warnings;
use strict;
use CGI;

local $| = 1;

my $cgi = new CGI;
my $string = localtime();
print $cgi->header();
print $cgi->start_html("Welcome");
print $cgi->h1("$string");
print $cgi->end_html();

print $cgi->header();
print $cgi->start_html("Welcome");
print $cgi->h1("$string");
print $cgi->end_html();

回答1:

Your question reveals a fundamental misunderstanding of how things work.

The sequence of events is:

1. The web server is configured to run a specific program when a specific URL is requested.
2. A browser makes an HTTP request asking for the resource.
3. The server runs the program, and captures its standard output stream, and sends that back to the browser.
4. The browser displays the content.

After the request/response cycle is completed, the transaction is over. The server does not know where exactly the content it sent went, whether it's being displayed in a window or was converted to ASCII art. It sends the content and its done with it (TCP keep-alives etc do not change this model).

Therefore, the statement "CGI script which keeps on flushing with current time in the same browser instead of printing a list of times" is devoid of meaning: The server cannot take back the output it has already sent.

Using JavaScript and XHR, you can update the contents of a certain element on a page with output from a CGI script.

However, now another fundamental question to which you don't seem to have paid any attention rears its head: What do you mean by current time?

回答2:

Switch to PSGI.

my $app = sub {
    my $env = shift;
    return sub {
        my $respond = shift;
        my $writer = $respond->([200, ['Content-Type', 'multipart/x-mixed-replace; boundary=time']]);
        while (1) {
            $writer->write(
                "--time\n" .
                "Content-Type: text/plain\n\n" .
                localtime . "\n"
            );
            sleep 1;
        }

        # will never arrive here, but
        # install a signal handler and call this for cleanup
        $writer->close;
    };
};

回答3:

Perhaps you want to provide a META Refresh header in your output so that the page auto-refreshes every second. But really I'd recommend using Javascript for this.