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Asked: 2026-06-13T13:52:16+00:00

I have prepared a sample application to get updates from server in real time

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I have prepared a sample application to get updates from server in real time using Cramp(Ruby) and SSE(HTML5).

I am getting following errors while accessing the html through http://localhost/sse_time.html

Errors:
Chrome:
  Uncaught Error: SECURITY_ERR: DOM Exception 18 sse_time.html:9
  Uncaught TypeError: Cannot read property 'key-preview' of undefined 

Firefox:
  Error: The character encoding of the HTML document was not declared. The document will render with garbled text in some browser configurations if the document contains characters from outside the US-ASCII range. The character encoding of the page must to be declared in the document or in the transfer protocol.
Line: 0

  Error: The connection to http://localhost:3000/time was interrupted while the page was loading.
  Line: 9

sse_time.html

<!DOCTYPE html>
<html>
<body>
<h1>Getting server updates</h1>
<div id="result"></div>
<script>
  if (!!window.EventSource) {

    var source = new EventSource('http://localhost:3000/time');

    source.addEventListener('message', function(e) {
      console.log(e.data);
    }, false);

    source.addEventListener('open', function(e) {
      // Connection was opened.
      console.log('Connection was opened.');
    }, false);

    source.addEventListener('error', function(e) {
      if (e.readyState == EventSource.CLOSED) {
        // Connection was closed.
        console.log('Connection was closed.');
      }
    }, false);

  } else {
    document.getElementById("result").innerHTML="Sorry, your browser does not support server-sent events...";
  }
</script>

</body>
</html>

app/actions/time_action.rb

class TimeAction < Cramp::Action
  self.transport = :sse

  periodic_timer :send_latest_time, every: 5

  def send_latest_time
    render "Current time : #{Time.now}"
  end
end

where line 9 is var source = new EventSource('http://localhost:3000/time');

If I hit http://localhost:3000/time in chrome, it shows time after each 5 seconds without any errors.

However with PHP code it works fine replacing URI http://localhost:3000/time with stream.php in sse_time.html

stream.php

<?php
header('Content-Type: text/event-stream');
header('Cache-Control: no-cache'); // recommended to prevent caching of event data.

/**
 * Constructs the SSE data format and flushes that data to the client.
 *
 * @param string $id Timestamp/id of this connection.
 * @param string $msg Line of text that should be transmitted.
 */
function sendMsg($id, $msg) {
  echo "id: $id" . PHP_EOL;
  echo "data: $msg" . PHP_EOL;
  echo PHP_EOL;
  ob_flush();
  flush();
}

$serverTime = time();

sendMsg($serverTime, 'server time: ' . date("h:i:s", time()));

Here stream.php and sse_time.html resides at same locaation.

Would anyone please guide me to fix this issue?

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1 Answer

  1. Editorial Team

    Referring to CASE STUDY: REAL-TIME UPDATES IN STREAM CONGRESS

    A significant issue to keep in mind with EventSource is that cross-domain connections are not allowed. This means that the Cramp app must be served from the same streamcongress.com domain as the main Rails app.

    I realize the html page also needs to be part of the cramp application(though there is alternative). So I made following changes and it worked.

    Modified app/actions/home_action.rb based on Cramp chat using Redis Pub/Sub + WebSockets

    class HomeAction < Cramp::Action
  @@template = ERB.new(File.read(PocRailsCramp::Application.root('app/views/index.html.erb')))

  def start
    render @@template.result(binding)
    finish
  end
end

    and the content of app/views/index.html.erb is same as the content of sse_time.html in the the question itself.

    Now hitting http://localhost:3000 started showing server time in each 5 seconds on browser console.

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