Hello World extension broke whole Flarum

HelpLeecher

So I created Hello World application following this tutorial:
https://discuss.flarum.org/d/1608-extension-development-using-composer-repositories-path

My bootstrap.php contains the same code that is given in the official documentation's Hello World extension.

I run my composer update and stuff, then enabled the extension from Admin Dashboard. As soon as I enabled it I started getting this error:
RuntimeException
Failed to start the session because headers have already been sent by "/srv/users/serverpilot/apps/myapplication/public/workbench/flarum-ext-yogi/bootstrap.php" at line 4.

Here's my callstack information:
http://i.imgur.com/myayCyt.png

How can I fix this? What is the problem?

luceos

the bootstrap file has incorrect code, can you paste its contents?

HelpLeecher

luceos
This is all it is, no extra spaces, no extra characters:
<?php

return function () {
echo 'Hello world!';
};

UaMV

HelpLeecher I'm at the same place you are. This will get your Hello world! to the screen upon activation:

<?php
  echo 'Hello world!';

luceos

HelpLeecher the problem is you are parsing the hello world to the output buffer. After that the Flarum engine tries to create the content for the page, but cannot output that buffer because it was already initiated. If you want to test whether your extension is working, simply add exit:

<?php

return function() {
    echo "Hello world!";
    exit;
};

HelpLeecher

luceos Thanks, it worked.
I think someone needs to update the documentation.