Using PHP Output Bufferering to Issue JavaScript During Processing

I have some PHP code that is receiving a开发者_运维百科nd processing large images. I'd like to echo out some JavaScript at certain points while the image is being processed to update the DOM with jQuery. Here is some sample code, but it isn't working. It just waits the entire 5 seconds and then makes the alerts happen back to back. I want it to do the first alert immediately and then next alert after 5 seconds.

ob_start();

echo '<script type="text/javascript">alert(\'1...\');</script>';

ob_flush();

sleep(5);

ob_start();

echo '<script type="text/javascript">alert(\'2...\');</script>';

ob_flush();

Can anyone help?

Most browsers buffer content until a certain size is reached. Try making your script blocks longer by padding them with something.

Also: You should call flush, not just ob_flush, and make sure zlib compression is turned off.

I have some PHP code that is receiving and processing large images. I'd like to echo out some JavaScript at certain points while the image is being processed to update the DOM with jQuery.

This may be out-of-scope for what you have to get done, but I'd use AJAX for this. You can certainly get what you want to occur, but the approach isn't good in the long term.

Instead of submitting the whole page and waiting for it to come back at a crawl, use an AJAX request to upload the image and get the result. Then a timer on the client can issue separate AJAX "how far done are you?" requests. The two PHP instances would communicate via setting a "done" flag on the job entry in a database, etc.

While it makes the client-side stuff a bit more complex, it is much easier to handle user interaction (such as allowing the user to cancel a long-running job) and makes your PHP code a lot more tightly-focused.

Adding this to the top of the script will work:

for ($i = 0; $i < ob_get_level(); $i++) { ob_end_flush(); }
ob_implicit_flush(1);

As far as I know, ob_implicit_flush(1) forces a flush on every output statement. So the other ob_start() and ob_flush() calls wouldn't be necessary. I don't know if that works for you.

<?php

for ($i = 0; $i < ob_get_level(); $i++) { ob_end_flush(); }
ob_implicit_flush(1);

echo '<script type="text/javascript">alert(\'1...\');</script>';

sleep(5);

echo '<script type="text/javascript">alert(\'2...\');</script>';

?>

Following is working in FF4:

<?php
echo '<script type="text/javascript">alert("1");</script>';
flush();
sleep(5);
echo '<script type="text/javascript">alert("2");</script>';
?>

I implemented a chat "server" with something like that long ago. It was working.

This ob_* stuff isn't helpful for this.