Sequentioal requests with Mojo::IOLoop::Delay - perl

Question

I need to get list of URLs in non-blocking mode, but not in parallel. It should be sequential requests one by one. How can I realize that?
I cannot find examples. Documentation and articles highlight only parallel execution.
Now my code looks like the following (simplified):
my $delay = Mojo::IOLoop::Delay->new;
$delay->steps(
sub {
build_report();
say "done";
}
);
sub parse_data {
...;
my $url = shift #urls;
my $end = $delay->begin;
$ua->get( $url => \&parse_data );
$end->();
}
my $end = $delay->begin;
$ua->get( $url => \&parse_data );
$end->();
$delay->wait;
I want to avoid multiple closures by using Mojo::IOLoop::Delay.

Answer 1

I have just started looking at Mojo::IOLoop myself for a project and I'm not au fait with it yet. But I think the simplest way is to build an array of closures and pass it to $delay->steps.
use strict;
use warnings 'all';
use feature 'say';
use Mojo;
use constant URL => 'http://stackoverflow.com/questions/tagged/perl';
STDOUT->autoflush;
my $ua = Mojo::UserAgent->new;
my $delay = Mojo::IOLoop::Delay->new;
my #urls = ( URL ) x 10;
my #steps = map {
my $url = $_;
sub {
my $end = $delay->begin;
$ua->get( $url => sub {
my ( $ua, $txn ) = #_;
$end->();
if ( my $err = $txn->error ) {
say $err->message;
}
else {
my $res = $txn->success;
say "#{$res}{qw/ code message /}";
}
});
}
} #urls;
$delay->steps( #steps, sub { say 'Done' } );
Mojo::IOLoop->start unless Mojo::IOLoop->is_running;
output
200 OK
200 OK
200 OK
200 OK
200 OK
200 OK
200 OK
200 OK
200 OK
Done
200 OK
Note that Done is printed before the status line of the final get, because I have called $end->() immediately the callback arrives, assuming that any handling of the response doesn't need to be synchronised
If you don't want that then just move $end->() to the end of the callback. Then the delay will wait until the output has been generated before sending another request

Answer 2

Sequential requests very easy to implement.
Web server
#!/usr/bin/perl
use Mojo::Base -strict;
use Mojolicious::Lite;
get '/' => sub {
my $c = shift->render_later;
$c->delay(sub {
my $delay = shift;
$c->ua->get('https://google.ru' => $delay->begin);
}, sub {
my ($delay, $tx) = #_;
$tx->res->body; # body of the google.ru
$c->ua->get('https://twitter.com' => $delay->begin);
}, sub {
my ($delay, $tx) = #_;
$tx->res->body; # body of the twitter.com
$c->render(text => 'Done');
});
};
app->start;
Script
#!/usr/bin/perl
use Mojo::Base -strict;
use Mojo::IOLoop;
use Mojo::UserAgent;
my $ua = Mojo::UserAgent->new;
Mojo::IOLoop->delay(sub {
my $delay = shift;
$ua->get('https://www.google.ru' => $delay->begin);
}, sub {
my ($delay, $tx) = #_;
$tx->res->body; # body of the google.ru
$ua->get('https://twitter.com' => $delay->begin);
}, sub {
my ($delay, $tx) = #_;
$tx->res->body; # body of the twitter.com
warn 'DONE';
})->wait;
Script (dynamic requests)
Example here