user5294195 user5294195 - 1 year ago 61
Apache Configuration Question

SSE not sending events until the script has finished executing?

I am having a issue where SSE events wait until the script has finished executing before finally sending the data, after hours of searching for a plausible explanation or solution, I have found nothing.

I have found a example however that works on that website, however taking that code onto my server, it doesn't work. (URL:

In this example I have noticed a header of

Transfer-Encoding: chunked
When I had tried to make Apache send this header through .htaccess with
Header set
, the response code turned to "(failed)".

I also noticed the example didn't have a
, where as the one from my server does.

This was all tested on Chrome v.53.0.2785.116m

After that I decided to take it to the stacks.

Here is a example:

header('Content-Type: text/event-stream');
header('Cache-Control: no-cache');

function sendMsg($id, $msg) {
echo "id: $id" . PHP_EOL;
echo "data: $msg" . PHP_EOL;
echo PHP_EOL;

while ($x < 5) {
$serverTime = time();
sendMsg($serverTime, 'server time: ' . date("h:i:s", time()));

If I were to perform a request to this script, I would get these headers:

HTTP/1.1 200 OK
Date: Tue, 27 Sep 2016 22:34:11 GMT
Server: Apache
Cache-Control: no-cache
Vary: Accept-Encoding,User-Agent
Content-Encoding: gzip
Content-Length: 91
Keep-Alive: timeout=15, max=43
Connection: Keep-Alive
Content-Type: text/event-stream

I will not get any data from this until the script had finished executing.

At this point I'm unclear if its Apache, or PHP that is at fault here, but from what I can tell the server is at fault.
I've tried version of PHP ranging from 5.5-7, all with no luck.

Any ideas on whats going wrong here and how to fix it?

I tried the same script on another server and it had worked properly, and sent the following headers:

HTTP/1.1 200 OK
Server: nginx
Date: Wed, 28 Sep 2016 15:40:00 GMT
Content-Type: text/event-stream;charset=UTF-8
Transfer-Encoding: chunked
Connection: keep-alive
Keep-Alive: timeout=15
Cache-Control: no-cache
ngpass_ngall: 1

Answer Source

I suspect the problem is gzip-ing the output. (Your working nginx server is not doing that.)

In your .htaccess file, can you try both of these:

php_flag zlib.output_compression off
SetEnv no-gzip 1

(Borrowed from and its answers.)

BTW, you shouldn't need to add the chunking header yourself; it will be set if the output is chunked.

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