How do I close a connection early?

It's necessary to send these 2 headers:

Connection: close
Content-Length: n (n = size of output in bytes )

Since you need know the size of your output, you'll need to buffer your output, then flush it to the browser:

// buffer all upcoming output
ob_start();
echo 'We\'ll email you as soon as this is done.';

// get the size of the output
$size = ob_get_length();

// send headers to tell the browser to close the connection
header('Content-Length: '.$size);
header('Connection: close');

// flush all output
ob_end_flush();
ob_flush();
flush();

// if you're using sessions, this prevents subsequent requests
// from hanging while the background process executes
if (session_id()) {session_write_close();}

/******** background process starts here ********/

Also, if your web server is using automatic gzip compression on the output (ie. Apache with mod_deflate), this won't work because actual size of the output is changed, and the Content-Length is no longer accurate. Disable gzip compression the particular script.

For more details, visit http://www.zulius.com/how-to/close-browser-connection-continue-execution


You can use Fast-CGI with PHP-FPM to use the fastcgi_end_request() function. In this way, you can continue to do some processing while the response has already been sent to the client.

  • example of how to use fastcgi_finish_request() (Nov 2010)

You find this in the PHP manual here: FastCGI Process Manager (FPM); But that function specifically is not further documented in the manual. Here the excerpt from the PHP-FPM: PHP FastCGI Process Manager Wiki:

fastcgi_finish_request()

Scope: php function

Category: Optimization

This feature allows you to speed up implementation of some php queries. Acceleration is possible when there are actions in the process of script execution that do not affect server response. For example, saving the session in memcached can occur after the page has been formed and passed to a web server. fastcgi_finish_request() is a php feature, that stops the response output. Web server immediately starts to transfer response "slowly and sadly" to the client, and php at the same time can do a lot of useful things in the context of a query, such as saving the session, converting the downloaded video, handling all kinds of statistics, etc.

fastcgi_finish_request() can invoke executing shutdown function.

Note: fastcgi_finish_request() has a quirk where calls to flush, print, or echo will terminate the script early.

To avoid that issue, you can call ignore_user_abort(true) right before or after the fastcgi_finish_request call:

ignore_user_abort(true);
fastcgi_finish_request();

Complete version:

ignore_user_abort(true);//avoid apache to kill the php running
ob_start();//start buffer output

echo "show something to user";
session_write_close();//close session file on server side to avoid blocking other requests

header("Content-Encoding: none");//send header to avoid the browser side to take content as gzip format
header("Content-Length: ".ob_get_length());//send length header
header("Connection: close");//or redirect to some url: header('Location: http://www.google.com');
ob_end_flush();flush();//really send content, can't change the order:1.ob buffer to normal buffer, 2.normal buffer to output

//continue do something on server side
ob_start();
sleep(5);//the user won't wait for the 5 seconds
echo 'for diyism';//user can't see this
file_put_contents('/tmp/process.log', ob_get_contents());
ob_end_clean();

The following PHP manual page (incl. user-notes) suggests multiple instructions on how to close the TCP connection to the browser without ending the PHP script:

  • Connection handling Docs

Supposedly it requires a bit more than sending a close header.

OP then confirms: yup, this did the trick: pointing to user-note #71172 (Nov 2006) copied here:

Closing the users browser connection whilst keeping your php script running has been an issue since [PHP] 4.1, when the behaviour of register_shutdown_function() was modified so that it would not automatically close the users connection.

sts at mail dot xubion dot hu Posted the original solution:

<?php
header("Connection: close");
ob_start();
phpinfo();
$size = ob_get_length();
header("Content-Length: $size");
ob_end_flush();
flush();
sleep(13);
error_log("do something in the background");
?>

Which works fine until you substitute phpinfo() for echo('text I want user to see'); in which case the headers are never sent!

The solution is to explicitly turn off output buffering and clear the buffer prior to sending your header information. Example:

<?php
ob_end_clean();
header("Connection: close");
ignore_user_abort(true); // just to be safe
ob_start();
echo('Text the user will see');
$size = ob_get_length();
header("Content-Length: $size");
ob_end_flush(); // Strange behaviour, will not work
flush(); // Unless both are called !
// Do processing here 
sleep(30);
echo('Text user will never see');
?>

Just spent 3 hours trying to figure this one out, hope it helps someone :)

Tested in:

  • IE 7.5730.11
  • Mozilla Firefox 1.81

Later on in July 2010 in a related answer Arctic Fire then linked two further user-notes that were-follow-ups to the one above:

  • Connection Handling user-note #89177 (Feb 2009)
  • Connection Handling user-note #93441 (Sep 2009)

Tags:

Php

Ajax

Jquery

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