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Digg Chapter 7. Connection handling
Note:
The following applies to 3.0.7 and later. Internally in PHP a connection status is maintained. There are 3 possible states:
When a PHP script is running normally the NORMAL state, is active. If the remote client disconnects the ABORTED state flag is turned on. A remote client disconnect is usually caused by the user hitting his STOP button. If the PHP-imposed time limit (see set_time_limit()) is hit, the TIMEOUT state flag is turned on.
You can decide whether or not you want a client disconnect to cause
your script to be aborted. Sometimes it is handy to always have your
scripts run to completion even if there is no remote browser receiving
the output. The default behaviour is however for your script to be
aborted when the remote client disconnects. This behaviour can be
set via the ignore_user_abort
Your script can also be terminated by the built-in script timer.
The default timeout is 30 seconds. It can be changed using
the One thing to note is that both the ABORTED and the TIMEOUT states can be active at the same time. This is possible if you tell PHP to ignore user aborts. PHP will still note the fact that a user may have broken the connection, but the script will keep running. If it then hits the time limit it will be aborted and your shutdown function, if any, will be called. At this point you will find that connection_status() returns 3. Code Examples / Notes » features.connection_handlingpulstar
These functions are very useful for example if you need to control when a visitor in your website place an order and you need to check if he/she didn't clicked the submit button twice or cancelled the submit just after have clicked the submit button. If your visitor click the stop button just after have submitted it, your script may stop in the middle of the process of registering the products and do not finish the list, generating inconsistency in your database. With the ignore_user_abort() function you can make your script finish everything fine and after you can check with register_shutdown_function() and connection_aborted() if the visitor cancelled the submission or lost his/her connection. If he/she did, you can set the order as not confirmed and when the visitor came back, you can present the old order again. To prevent a double click of the submit button, you can disable it with javascript or in your script you can set a flag for that order, which will be recorded into the database. Before accept a new submission, the script will check if the same order was not placed before and reject it. This will work fine, as the script have finished the job before. Note that if you use ob_start("callback_function") in the begin of your script, you can specify a callback function that will act like the shutdown function when our script ends and also will let you to work on the generated page before send it to the visitor. lee
The point mentioned in the last comment isn't always the case. If a user's connection is lost half way through an order processing script is confirming a user's credit card/adding them to a DB, etc (due to their ISP going down, network trouble... whatever) and your script tries to send back output (such as, "pre-processing order" or any other type of confirmation), then your script will abort -- and this could cause problems for your process. I have an order script that adds data to a InnoDB database (through MySQL) and only commits the transactions upon successful completion. Without ignore_user_abort(), I have had times when a user's connection dropped during the processing phase... and their card was charged, but they weren't added to my local DB. So, it's always safe to ignore any aborts if you are processing sensitive transactions that should go ahead, whether your user is "watching" on the other end or not. ej
I don't think the first example given below will occur in the real world. As long as your order handling script does not output anything, there's no way that it will be aborted before it completes processing (unless it timeouts). PHP only senses user aborts when a script sends output. If there's no output sent to the client before processing completes, which is presumably the case for an order handling script, the script will run to completion. So, the only time a script can be terminated due to the user hitting stop is when it sends output. If you don't send any output until processing completes, you don't have to worry about user aborts. bg
Confirmed. User presses STOP button. This sends a RST packet and closes the connection. PHP is most certainly immediately affected (i.e., the script is stopped, whether or not any output is pending for the user, or even if script is just grinding away on a database without having output anything). ignore_user_abort() exists to prevent this. If user STOPS, script ignores the RST and runs to completion (the output is apparently ignored by apache and not sent to the user, who sent the RST and closed the TCP connection). If user's connection just vanishes (isp problem, disconnect, whatever), and there is no RST sent by user, then eventually the script will timeout. arr1
Closing the users browser connection whilst keeping your php script running has been an issue since 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(); // optional 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 hrgan
As it was said, connection handling is very useful when web application need to do something in background. I found it very useful when application need something from database, wrap that data with template, create some html files and save it to filesystem. And all that on server with heavy load. Without connection handling - function ignore_user_abort() - this process can be interrupted by user and final step will never be done.
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