[RESOLVED] Need a little help with flushing.

sartavius

Okay, so I'm playing with an idea for my chat system. I want to offer an option of a 'streaming' style where the window stays alive and displays the messages automatically when one is received.

I know that AJAX or json would be a better and more server-friendly way of doing this but quite frankly, I know about as much javascript and json just to get me by and I wouldn't know where to begin to take it to the level that I'm needing.

Therefore. . .I'm playing with flush and sleep for the time being. I have everything worked out except for the most important part: show the messages! lol

Here is the snippet of code in question:

if (ob_get_level() == 0) ob_start();
    $row = mysql_fetch_array($outres);
    for ($i = 0; $i<10; $i++){
      echo '<!-- bufferme -->';
      echo str_pad('',4096)."\n";
      ob_flush();
      flush();
      sleep(10);
      }
   output_message($row);
  } else {
    // This will be some message for when the 'stream' dies with a 'reconnect' button
  }

What I'm getting right now is the -- bufferme -- every 10 seconds and then when the count of 10 (as set in the "for" area) is over, THEN it prints whatever messages were received.

I had it setup a bit different before but what it did then was to print the same message over and over until that count of 10 was over.

What am I missing here? Oh, and I hope I'm making sense and people are able to follow what I'm trying to explain! 😃

johanafm

Indent your code properly and what happens should come as no surprise. (If it still does, ask again)

if (ob_get_level() == 0)
	ob_start();
$row = mysql_fetch_array($outres);
for ($i = 0; $i<10; $i++)
{
	echo '<!-- bufferme -->';
	echo str_pad('',4096)."\n";
	ob_flush();
	flush();
	sleep(10);
}
output_message($row);

sartavius

johanafm;10989120 wrote:
Indent your code properly and what happens should come as no surprise. (If it still does, ask again)
if (ob_get_level() == 0)
	ob_start();
$row = mysql_fetch_array($outres);
for ($i = 0; $i<10; $i++)
{
	echo '';
	echo str_pad('',4096)."\n";
	ob_flush();
	flush();
	sleep(10);
}
output_message($row);

I do understand why it's doing what it's doing, I'm just stumped about a couple of things. If I stick output_message($row) up in the for/flush loop it just keeps showing the same message over and over instead of just ONCE until there is another message(s). Does that make sense or am I explaining it in a ridiculous way?

sartavius

No one at all? Is there a place/forum here to hire someone for help?

Weedpacket

My bad. I was too busy working to pay the bills.

Notice that on the page for [man]ob_flush[/man] it says:

This function does not destroy the output buffer like [man]ob_end_flush/man does.

That would explain the duplicate messages.

johanafm

Weedpacket;10989152 wrote:
That would explain the duplicate messages.

Actually it doesn't explain it at all. While it's true that the buffer is not destroyed when calling ob_flush as opposed to ob_end_flush(), the buffer is still used and emptied when flush is called.

However, looping over the echo statement 10 times explains why the same message is sent 10 times.

$row = mysql_fetch_array($outres);
for ($i = 0; $i<10; $i++)
{
	output_message($row); 
}

sartavius

johanafm;10989156 wrote:
Actually it doesn't explain it at all. While it's true that the buffer is not destroyed when calling ob_flush as opposed to ob_end_flush(), the buffer is still used and emptied when flush is called.

However, looping over the echo statement 10 times explains why the same message is sent 10 times.
$row = mysql_fetch_array($outres);
for ($i = 0; $i<10; $i++)
{
	output_message($row); 
}

I see what you're saying and that's what I assumed also, but I'm not sure how else to keep the flush going without that loop...?

johanafm

Once again, PHP's output buffering has nothing at all to do with the issue!

The only issue you are dealing with is the web servers output buffer. The web server buffers all output until the buffer is filled, and then sends the buffer contents to the browser. This is obviously separate from PHP's output buffer, and therefor unrelated. As such, the only thing you need to do is fill the web servers output buffer, which you easily achieve with str_pad.

When do you need to fill the web server buffer? Any time you want something to be sent to the browser that would otherwise not be sent.

Consider the following script

function out_fillbuff($s)
{
	# Set this to match your web server's buffer size
	static $bufsize = 8192;
	echo $s . str_repeat(' ', $bufsize - strlen($s));
}

$s = 'starting loop without padding output to 4k bytes<br/>';
out_fillbuff($s);
for ($i = 0; $i < 5; ++$i)
{
	$s = 'line ' . $i . '<br />';
	echo $s;
	usleep(100000);
}

$s = 'Now filling buffer on all output<br/>';
out_fillbuff($s);
for ($i = 0; $i < 5; ++$i)
{
	$s = 'line ' . $i . '<br />';
	out_fillbuff($s);
	usleep(500000);
}

Weedpacket

Okay, I've got a few more brain cells together and I think I've got a quorum now...

To be honest, I remember hacking stuff like this last century, and I wouldn't want to go back. It really wouldn't be that difficult to put together a solution based on JavaScript, and the time spent learning it (which could easily be less than what has already been spent) would be much more rewarding in terms of doing other things later - even if you opt for a JavaScript framework that hides all the Ajax implementation details.

The fact that it won't require dedicating web- and database-server connections for each user would just be a bonus.

Oh, yeah, was going to ask: How do you decide at the end of each ten seconds what messages to send? Because at the moment it looks like you're collecting all the messages at the start and then drip-feeding the rows from that collection at ten-second intervals. when that collection is exhausted do you loop back and collect another batch?

johanafm

Weedpacket;10989213 wrote:
Okay, I've got a few more brain cells together and I think I've got a quorum now...

To be honest, I remember hacking stuff like this last century, and I wouldn't want to go back.

I completely agree. The only reason I didn't even comment on it was that he appears to be aware of this allready, since

sartavius;10989096 wrote:
I know that AJAX or json would be a better (...) way.

Therefore. . .I'm playing with flush and sleep for the time being.

Weedpacket

I read that too, but I figured the time taken to learn the older approach would be better spent learning the newer one...

sartavius

Marking this thread resolved as I sat down and forced myself to learn what I needed with AJAX and got it running perfectly!