When I call PHP's ob_flush() function on my localhost (via MAMP) I get the following error:
Notice: ob_flush() [ref.outcontrol]:
failed to flush buffer. No buffer to
flush.
The only solution I can find is to prefix it with #, but this doesn't seem like a real solution to me. What's causing the problem?
The error message would seem to imply that you're not actually using output buffering when you call ob_flush(). Have you called ob_start() previous to invoking ob_flush()?
If you want to use ob_flush you must first call ob_start() - desirably at the top of your page.
Not sure if it fits your needs but you might want to also try the plain old flush(), just guessing.
Related
I hired someone to write an API for me in PHP and MySQL and now have to maintain it myself. I don't know php as well as other languages.
I noticed at the start of most of the php files they have:
ob_start();
I understand that this opens a new output buffer. The thing is that they never flush the buffer. The code had been working fine but I've had a lot of optimization issues, slow server responses, etc.
How is it that they don't have to flush the buffer but the response is still returning?
An example would be:
ob_start();
include "nusoap.php";
include "config.php";
require_once "class.Database.php";
$client = new nusoap_client($config['apiURL'].'/server.php',false, false, false, false, false, 600, 600);
... process the $_GET and build a $result ...
print_r($result);
Obviously the ... process ... is a wide open thing. But I'm not seeing anywhere in there that does any sort of flush or reading the ob contents. I've also searched all the includes and don't see one in there either.
I checked and implicit_flush is set to Off on this server. Since we did move this code from another server possibly on that server it was on. But still currently this API is working on this server.
The reason I said "not that I can find" when someone asked if there was an ob_get_contents() is because there are include files (including nusoap.php) that include other files and while I've grepped through them and tried to trace them, I might have missed something and am still searching. But so far it appears to my eye that no flush or get_contents is happening.
One possible answer is to say "NO, there has to either be an implicit_flush set in the php.ini file, or an implicit_flush() command somewhere, or another flush command somewhere, or getting the contents of the buffer somewhere - or the contents would never output." To me that is what the manual suggests. But sometimes there are loopholes and PHP seems to be a language of loopholes.
SOLVED
Indeed I did a simple test:
<?php
ob_start();
echo "Whats Up Doc!";
?>
and the output is seen in the browser.
PHP ob_start() function works by catching all output to buffer and then implicitly output this buffer on script end.
You may execute ob_end_clean() to discard (clean) buffer.
In Your example 'print_r($result);' will send output to buffer and then PHP interpreter will send buffer to client (http server/console).
PS. Function ob_implicit_flush() has different meaning. It just flush buffer on every output call (like print or echo), and do not have effect on script finish.
Good day!
I am having some issues with getting the echo statement to output before the execution of the exec()
<?
if (isset($_POST['ipaddress'])) {
$escaped_command = escapeshellcmd($_POST['ipaddress']);
if(filter_var($escaped_command, FILTER_VALIDATE_IP)) {
echo "Gleaning ARP information, please wait..";
$command = exec('sudo /sbin/getarp.exp');
The echo statement is being outputted after the execution of the $command. The execution time can be anywhere from 15-30 seconds depending on how large the ARP table on the remote router is. Is there an order of operations that I am not aware of? It appears that all the statements within the if statement are executed in parallel and not by line by line as I had assumed.
I would rather not a solution be provided, but some documentational links that would lead me to finding a solution. I have searched what I could, but was not able to find a viable solution.
Any help would be appreciated.
Thanks.
This is happening because the script will run in its entirety before any result/output is sent to the browser.
In PHP there is a concept of "output buffering".
Whenever you output something (e.g. using echo, print, etc.) the text is thrown into a buffer. This buffer is only sent at certain times (at the end of the request, for instance, or when the buffer is full).
In order to empty the buffer (to "flush" it) you need to do it manually. The flush() function will do this. Sometimes you also need to call ob_flush() (this is if you have opened custom output buffers yourself). It is generally a good idea to just call both functions and be done with it:
echo 'Wait a few seconds...';
flush(); ob_flush();
sleep(3);
echo ' aaand we are done!';
See Output Buffering Control for more information on output buffering in PHP.
This is probably an issue with the output buffer. PHP buffers output and writes it to the browser in chunks. Try adding a call to ob_flush() between the echo and the exec(); this will force PHP to write the current contents of the buffer to the browser.
By default, php does not send any of the output until the php script is done running completely. There is a solution. However, I hear it is a little browser dependent. I would test it on different systems and browsers to see if it is working:
ob_implicit_flush (true)
Put that before any of your echo/print commands and that should allow anything printed to show right up on the browser.
A more universal approach would be to integrate your page with asynchronous javascript. A process commonly referred to as "AJAX". It is a little more difficult because it requires the use of many interacting scripts, some client-side and some server-side. However, AJAX is the defacto way to do thing like this on the web.
Final update
Seems like I did make a very simple error. Since I already have a stream implementation I can just not start reading from the stream :D
I'm trying to achieve fire-and-forget like functionality in PHP.
From php.net
<?php
ignore_user_abort(true);
header("Content-Length: 4");
header("Connection: Close");
echo "abcd";
flush();
sleep(5);
echo "Text user should not see"; // because it should have terminated
?>
This works if I open the script with a browser. (shows "abcd").
But if I open it with file_get_contents or some stream library it will wait for ~5 seconds and show the second text as well.
I'm using PHP 5.2.11 / Apache 2.0
Update
I seems there is some confusion about what I'm trying to accomplish.
I don't want to hide output using output buffers (that's stupid). I want to have the client terminate before the server starts a possibly lengthy process (sleep(5)) and I don't want the client to wait for it (this is what fire-and-forget means, sort off).
The use of output buffers is merely a side effect. I've amended the sample code without the use of output buffers.
What I don't understand is: why does this script behave differently when accessing it from the browser vs. fetching it in PHP with file_get_contents("http://dev/test.php") or some stream library? What I've seen in testing is that for instance stream_get_contents will actually block for 5 seconds before it returns any output at all, the is quite the opposite of what I want.
Update2
Some more results:
The browser somehow responds to the flush(). I can't figure out how to replicate this behavior with streams in PHP, my streams keep blocking.
I've tried fread and found that it behaves similar to stream_get_contents.
Specifying a maxlength has no effect, it will still block for ~5 seconds.
Changing the blocking mode has no effect (other than generating a bunch more calls to stream_get_contents()). It will wait ~5 seconds before returning anything.
stream_set_read_buffer has no effect (tested on a PHP 5.3.5 sever)
The second portion of text is showing up because you're stopping output buffering with ob_end_flush() and ob_end_clean(). When that happens PHP outputs content as normal. Try something like the following:
<?php
ob_start(); // turn on output buffering
print "Text the user will see.";
ob_flush(); // send above output to the user and keep output buffering on
print "Text the user will never see";
ob_end_clean(); // empty the buffer and turn off output buffering. your script should end here.
?>
It's important for ob_end_clean() to appear at the end of the script. It empties the buffer and does not send its contents to the user, thus keeping everything after ob_flush() hidden.
How do you access the script using file_get_contents? How do you access it with your browser? If you access the script without "http://", of course it will never get executed. Use the same URL as in the browser.
Edit:
The browser will render the page even before the connection is closed. Even if you flush, I don't think the connection is closed. You can fire up Wireshark and check. stream_get_contents and file_get_contents will block until they have all the output. Even if you flushed, they can't be sure that there isn't more content. Since the content-length header didn't seem to make {file,stream}_get_contents return earlier, you probably need to implement your own buffering, ala. fopen, read, fclose.
Seems like I did make a very simple error. Since I already have a stream implementation I can just not start reading from the stream :D
I am using PHP and simpletest for unit testing. My tests work fine until I try and set the cookie
try{
setcookie($name,$cookie,$cookie_expires );
}catch Exception($e){
blah
}
The exception is thrown because simpletest has already written out header information so I get the following:
Unexpected PHP error [Cannot modify header information - headers already sent by (output started at /tests/simpletest/reporter.php:43)] severity [E_WARNING] in [blah_code.php line 280]
I've seen vague explanations on catching this with $this->expectException(new Exception()); but no further documentation or examples that work. Could someone provide a working example or point me to documentation? To be clear. This is NOT my code producing the output but rather SimpleTest.
One way to get around this is by using output buffering.
You can turn it on globally in PHP's configuration (and possibly in .htaccess), or you can use ob_start() and its related functions (ob_get_clean(), ob_end_flush(), etc). For example:
ob_start();
// your SimpleTest here.
// your header/ cookie manipulation here.
And then:
ob_end_clean(); // Stop buffering and dump everything (don't echo).
ob_end_flush(); // Stop buffering and echo out the buffer.
ob_get_clean(); // Stop buffering and return everything as a string.
Or any of the other related functions. I believe PHP calls ob_flush() at the end of a file if you don't.
You get this error when you have output before (header functions) setcookie($name,$cookie,$cookie_expires );.
Make sure you don't have any echos or html or text or anything(NOT EVEN A SPACE) before <?php of setcookie($name,$cookie,$cookie_expires );.
I can't seem to find a good answer on this anywhere. If I am running output buffering, and a die() is fired, does that kick off an ob_end_flush() as well?
Yes it does. Any time the script ends gracefully, the buffers will be emptied. The only non-graceful endings are if it segmentation faults or if it's killed (signal 9 SIG_KILL). The only place that die() does a hard-kill of the process is if you call it inside of a register_shutdown_function (But the buffers are flushed before the shutdown function is called, so there's no issue there). See Connection Handling for some more information...
Yes.
However, you can make the output empty if you have
register_shutdown_function('ob_clean');
earlier in the code.
In some cases we did not want to output the ob on a die().
I write this here in case it could help anyone who wants to do the same.