Long story short: I want to write client code that consumes a webservice, asynchronously receiving data, but need to be able to synchronously make program flow decisions by sending messages to the server.

I have an approach that works but I am certain it’s hacky and The Wrong Way®. It’s achieved by making the websocket transaction variable, $TX, available from outside the transaction. Any guidance on the right way to mix async with sync code here would be much appreciated. Note, the client is all I care about. I provide the server to match just to help test. Modules: Net::WebSocket::Server, Mojo::IOLoop, and Mojo::UserAgent. Thank you!

Sample server and client…

Save and run the server–

#!/usr/bin/env perl
use utf8;
use 5.10.2;
use Net::WebSocket::Server;

my $Running = 0;

Net::WebSocket::Server->new(
    listen => 8080,
    tick_period => 1,
    on_tick => sub {
        my $server = shift;
        return unless $Running;
        $_->send_utf8("Running")
            for $server->connections;
    },
    on_connect => sub {
        my ( $server, $connection ) = @_;
        $connection->on(
            ready => sub {
                my $connnection = shift;
                $connection->send_utf8("Connected… RUN|STOP");
            },
            utf8 => sub {
                my ( $connection, $message ) = @_;
                if ( uc $message eq "RUN" )
                {
                    $connection->send_utf8( $Running ? "Already runnin
+g" : "Starting to run…");
                    $Running = 1;
                }
                elsif ( uc $message eq "STOP" )
                {
                    $connection->send_utf8($Running ? "Stopping…" : "N
+ot running");
                    $Running = 0;
                }
                else
                {
                    $connection->send_utf8("Unknown command: $message"
+);
                }
            });
    })
    ->start;

[download]

Then the client–

#!/usr/bin/env perl
use 5.10.2;
use utf8;
use strictures;
use Mojo::UserAgent;

my $ua  = Mojo::UserAgent->new;

my $TX; # This is what has me thinking this is hacky/kludgy.
my $conn = $ua->websocket("ws://localhost:8080/" => sub {
    my $ua = shift;
    $TX = shift;
    say "WebSocket handshake failed!"
        and return unless $TX->is_websocket;

    $TX->on(finish => sub {
        my ( $tx, $code, $reason ) = @_;
        say "WebSocket closed with status $code.";
        exit;
    });

    $TX->on(text => sub {
        my $tx = shift;
        say "Server > ", +shift;
    });
});

my @command = qw/ RUN STOP /;
Mojo::IOLoop->recurring(5 => sub {
    my $command = $command[rand@command];
    say "Client > $command";
    $TX->send($command);
});

Mojo::IOLoop->start unless Mojo::IOLoop->is_running;

[download]

In reply to Mixing asynchronous data feed with synchronous program flow control by Your Mother

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