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I am testing HTML5 server sent events to see if I can use it in my project. I tried to follow the tutorial on http://www.html5rocks.com/en/tutorials/eventsource/basics and http://www.w3schools.com/html/html5_serversentevents.asp, but could not get it to work.

Here's my html (sse.html) and python cgi script (sse.py)：

<!DOCTYPE HTML>
<html>
<head>
<script type="text/javascript">
   var source = new EventSource("/cgi-bin/sse.py");
   source.onmessage = function(event) {
       console.log(event.data);
   };
</script>
</head>
<body>
Testing SSE!
</div>
</body>
</html>

sse.py as follows:

import sys
import datetime
import time

sys.stdout.write('Content-type: text/event-stream\r\n\r\n')

while True:
   now = datetime.datetime.now()
   sys.stdout.write('data: %s\r\n\r\n' % now)
   sys.stdout.flush()
   time.sleep(5)

I put 'sse.html' into 'c:\code\sse', and 'sse.py' into 'c:\code\sse\cgi-bin'. Then, I ran 'python -m CGIHTTPServer' to bring up the development web server.

When I connected to 'http://localhost:8000/sse.html', I didn't see the console logging the data received from the server. Instead, I saw a message saying that "Resource interpreted as Script but transferred with MIME type text/plain: "chrome-extension://hgimnogjllphhhkhlmebbmlgjoejdpjl/bar.js"."

Does anyone know what would be the problem?

Thanks!

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I modified 'sse.py' by trials and errors, and the code is working now. The new 'sse.py' is as follows:

import sys
import datetime
import time

sys.stdout.write('Content-type: text/event-stream \r\n\r\n')
now = datetime.datetime.now()
sys.stdout.write('data: %s \r\n' % now)
sys.stdout.write('retry: 1000\r\n\r\n')
sys.stdout.flush()

I am still trying to figure out how things work.

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  • I'm not sure 'retry' field solved your issue. But make sure that the response is encoded in UTF-8 and accordingly content-type header should be 'text/event-stream; charset=utf-8'.
    – Donghwan Kim
    Mar 25 '15 at 14:30
  • 'retry' is for setting up the interval for client to visit the script again. If I take out the statement for setup the 'retry' interval, and add one more '\r\n' to the statement above. The code will still work, but the time interval will become 3 seconds. What I don't understand is that based on what I read, it seems like we only need to set the content type once, and the client will always wait for message with 'data:' prefix. But the modified code shows that it seems like we need to specify the content type for each message.
    – Victor Gau
    Mar 25 '15 at 15:04
  • I don't know Python so can't give you a clear answer but something is clearly wrong. As the author of real-time web application framework, Cettia, I've never used retry field in dealing with Server-Sent Events. Because you seem to print raw HTTP message unlike what you read (they are using framework not deal with HTTP message lines directly), I suspect you should follow Chunked Transfer encoding.
    – Donghwan Kim
    Mar 25 '15 at 16:59
  • Then, the right plain message of HTTP response following event-stream format from Server-Sent Events spec will look like here See 'HTTP request/response for the client to receive data from the server' section. FYI, Vibe is a previous name of Cettia.
    – Donghwan Kim
    Mar 25 '15 at 17:00
  • I think you need to look up nph scripts.
    – ijw
    Aug 15 '17 at 18:52

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