tail on the browser

marcos rebelo

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Apr 20, 2012, 10:50:47 AM4/20/12

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Hi all

I'm getting crazy with the next script. The script is a sort of tail for a file on the server, when I start the server it works ok but when I try to reload the page doesn't work any more.

What am I doing wrong?

#!/usr/bin/env perl

use Mojolicious::Lite;

get '/' => sub {

my $self = shift;

$self->render('index');

};

my $loop = Mojo::IOLoop->singleton;

my $FILE_PATH = __FILE__; # Just for example now

websocket '/tail' => sub {

my $self = shift;

open(my $fh, '-|', 'tail', '-f', $FILE_PATH) or die $!;

$self->on(finish => sub {

close $fh;

$fh = undef;

} );

my $sub;

$sub = sub {

return if not defined $fh;

my $line = readline($fh);

$self->send_message( $line );

print "SEND: $line";

$loop->timer(0, $sub);

};

$sub->();

};

app->start;

__DATA__

@@ index.html.ep

<!DOCTYPE html>

<html>

<head>

<style>

.class-test {

width:10000px;

}

</style>

"use strict"

var create_line_div = function( text ) {

var div = $("<div></div>");

div.text(text);

return div;

};

var websocket;

var createWebSocket = function () {

websocket = new WebSocket("<%= $self->req->url->to_abs->scheme( $self->req->is_secure ? 'wss' : 'ws' )->path( '/tail' ) %>");

websocket.onmessage = function(evt) { $('.class-test').append( $( create_line_div( evt.data ) ) ) };

};

$( createWebSocket() );

</script>

</head>

<body>

Welcome to Tail!

</div>

</body>

</html>

Best Regards

Marcos Rebelo

--
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http://www.oleber.com/
Webmaster of http://perl5notebook.oleber.com

Gabriel Vieira

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Apr 20, 2012, 11:12:15 AM4/20/12

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CGI?

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marcos rebelo

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Apr 20, 2012, 11:37:05 AM4/20/12

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morbo script.pl

Tobias Oetiker

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Apr 20, 2012, 11:38:56 AM4/20/12

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Hi Marcos,

I have appended code I wrote for the a event-stream client which
might give you some inspiration ... note that the design is
different as the data source (tail -f) only runs once and not for
every client connecting ... in your design every connection gets
its own tail ....

package Signage2;
use Mojo::Base 'Mojolicious';

# This method will run once at server start
sub startup {
my $self = shift;
# Router
my $r = $self->routes;
my $log = $self->log;
$r->get('/' => 'index');
my $stream = $self->launch_arec;

my $loop = Mojo::IOLoop->singleton;

$r->get('/sound' => sub {
my $self = shift;
# Change content type
my $out_stream = $loop->stream($self->tx->connection);
$self->res->headers->content_type('text/event-stream');
# stop mojo from complaining about incomplete page
$self->render_later;
my $read_cb = $stream->on(read => sub {
my ($stream, $chunk) = @_;
while ($chunk =~ m{^(.+)[\r\n]+}g){
$self->write("event:log\ndata:".$1."\n\n");
}
});
my $close = sub {
my $stream = shift;
$self->write("event:log\ndata:Closed\n\n") if $self;
$log->info("closed client connection");
$self->finish;
};
$stream->once(close => $close);
$stream->once(error => $close);

my $unsubscribe = sub {
$stream->unsubscribe(read=>$read_cb);
$log->info("browser gone");
};

# when the connnection is dead, stop writing to it
$out_stream->once(timeout => $unsubscribe);
$out_stream->once(close => $unsubscribe);

});
}

sub launch_tail {
my $self = shift;
# Increase inactivity timeout for connection a bit
my $log = $self->log;
my $pid = open(my $fh,"-|", "tail","-f","$FILE_PATH") ||
die "can't fork: $!";
# Create stream

my $loop = Mojo::IOLoop->singleton;

my $stream = Mojo::IOLoop::Stream->new($fh);
# register with the io loop
my $id = $loop->stream($stream);
$stream->on(error => sub {
my ($stream, $err) = @_;
$loop->remove($id);
$log->error("Stream Error: $err");
});

$stream->on(close => sub {
my $stream = shift;
$log->info("closing connection to tail");
waitpid($pid,0);
$loop->remove($id);
});
$stream->start;
return $stream;
}

1;

Today marcos rebelo wrote:

--
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http://it.oetiker.ch to...@oetiker.ch ++41 62 775 9902 / sb: -9900

Ed W

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Apr 20, 2012, 1:13:18 PM4/20/12

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Hi

What am I doing wrong?

I think if you add some print statements you will find that you block on the close $fh ?

open(my $fh, '-|', 'tail', '-f', $FILE_PATH) or die $!;

$self->on(finish => sub {

close $fh;

$fh = undef;

} );

I haven't tested, but I think the close will wait for tail to finish and block?

Here is my attempt at a loop - note there are some extreme subtleties here and I would love for Sebastian to comment on the "correct" way to handle callbacks. What you should watch for is that some of the handles are weakened, and also the various shutdown functions throw ugly warning if you re-enter them. So you need to design your closedown so that you can kill either the tail which kills the web connection, or kill the web connection which kills the tail, all without creating a loop:

---

get '/system/logs' => 'system/logs';

# EventSource for log messages
get '/system/logs-es' => sub {
my $self = shift;
$self->render_later;

# Increase inactivity timeout for connection a bit

Mojo::IOLoop->stream( $self->tx->connection )->timeout(300);

# Change content type

$self->res->headers->content_type('text/event-stream');

$self->res->headers->header( 'X-Accel-Buffering' => 'no' );

my $pid = open( my $fh, "-|", "tail -F -n 0 /var/log/messages" );
defined($pid) || die "can't fork: $!";

# Create stream

my $stream = Mojo::IOLoop::Stream->new($fh);

$stream->timeout(0);
$stream->on(
    read => sub {
      my ( $stream, $chunk ) = @_;
      $chunk = $self->txt_to_html($chunk);
      $self->write("event:log\ndata:$chunk\n\n");
    }
);
$stream->on(

close => sub {
my $stream = shift;

      say "Close";    # DEBUG
      $self->finish("event:log\ndata:Log Closed<br><br>\n\n") if ( $self && $self->tx && !$self->tx->is_finished );
    }
);
$stream->on(
    error => sub {
      my ( $stream, $err ) = @_;
      say "MY Error: $err";    # DEBUG
      $self->finish("event:log\ndata:Error...Closing<br><br>\n\n") if ( $self && $self->tx && !$self->tx->is_finished );
    }
);

# Start listening to $fh
Mojo::IOLoop->singleton->stream($stream);

# Unsubscribe from "message" event again once we are done
$self->on(
    finish => sub {
      my $self = shift;
      say "Finishing";         # DEBUG
#    Mojo::IOLoop->singleton->drop($fh);
#    $stream->close;
      # Kill child
      kill( "TERM", $pid ) if $pid;
      undef $pid;
    }
);
};

@@ system/logs.html.ep
<div class="page-header">
<h1>System Logs</h1>
</div>
<p>Times in GMT/UTC</p>
<div class="row-fluid">
<div class="span12">
    <pre id="syslog">
    %== $self->txt_to_html( Mojo::Asset::File->new( path => '/var/log/messages' )->slurp );
    </pre>

    % content_for javascript_footer => begin
    <script>
      var events = new EventSource('<%= url_for '/system/log-es' %>');

      // Subscribe to "log" event
      events.addEventListener('log', function(event) {
        $("#syslog").append(event.data);
      }, false);
    </script>
    %end
</div>
</div>

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