How do I format a socket.io message to send to node.js with a Perl script?

I have a simple node.js server using socket.io that listens for messages. I am sending messages to the server with a Perl script. It seems that the server is receiving messages, but does not recognize the "channel" of the message. How to properly build node.js / socket.io messages to send with a Perl script?

Here is my node.js server:

var express = require('express');
var app = express.createServer();
var io = require('socket.io').listen(app);

app.listen(3000);

io.sockets.on('connection', function (socket) {
  console.log("In connection");
  socket.on('testevent', function (data) {
    console.log("In testevent");
    console.log(data);
  });
});

Here is the part of my Perl script that sends the message:

#$clientID is set to 1598760311220985572 earlier... obtained from a handshake

$uri = "http://192.168.3.13:3000/socket.io/1/xhr-polling/$clientID";

$message = "5:::{'name':'testevent','args':['hello!']}";

$request = HTTP::Request->new( 'POST', $uri );
$request->content( $message );

print $response = $browser->request( $request )->as_string;

Server log after message received from Perl script:

  info  - handshake authorized 1598760311220985572
  debug - client authorized for 
In connection
  debug - xhr-polling received data packet 5:::{'name':'testevent','args':['hello!']}

Thus, the node.js server seems to be receiving the message, but does not recognize the "testevent" channel, because I expect the server to write the string "In testevent" if it interprets the message correctly.

Perl, , , ?