How to access errno in PHP? - php

Question

A number of functions in PHP, that provide the same functionality as their libc namesakes, return FALSE to indicate a failure.
Is there a way to get more details about the actual error? In C I'd code something like:
if (unlink(path)) {
switch(errno) {
case ENOENT: .....
case ENAMETOOLONG: ...
....
default: warn(path);
}
}
What is the PHP way?

Answer 1

There is no errno as in libc. Some libs offer similar functionality (like i.e. mysql_errno(), curl_errno()). If you are using PHP5, you may try to use error_get_last()

Answer 2

This completely depends on what library you're working with. Different libraries have different ways of retrieving the error, oftentimes with a function. For example in the (outdated) MySQL library, you use mysql_error() to return the specific error message of the last error occurred.

Answer 3

I'm not sure if its possible, but you can try the function
error_get_last()
It will return the last error that occurred.
Sadly, there is not more "built in" option for this lib, so you should better do checks like:
if (file_exists($file)) // check if the file exists
and
if (is_writable($file)) // check if php can write to the file
so you can know why its could be failed.

Answer 4

errno is Predefined Constants error http://php.net/manual/en/errorfunc.constants.php if you want to handle error you can use ob_start instead of set_error_handler
<?php
error_reporting(E_ALL);
ob_start('error_handler');
function error_handler($output) {
$errno = array(
"1" => "E_ERROR",
"2" => "E_WARNING",
"4" => "E_PARSE",
"8" => "E_NOTICE",
"16" => "E_CORE_ERROR",
"32" => "E_CORE_WARNING",
"64" => "E_COMPILE_ERROR",
"128" => "E_COMPILE_WARNING",
"256" => "E_USER_ERROR",
"512" => "E_USER_WARNING",
"1024" => "E_USER_NOTICE",
"2048" => "E_STRICT",
"4096" => "E_RECOVERABLE_ERROR",
"8192" => "E_DEPRECATED",
"16384" => "E_USER_DEPRECATED",
"32767" => "E_ALL"
);
if(error_get_last())
{
$error = error_get_last();
$output = "";
foreach($error as $info => $string) {
if ($info == "type")
$output.= "{$info}: {$string} - {$errno[$string]}\n";
else
$output.= "{$info}: {$string}\n";
}
}
return $output;
}
undefinedFunc();
/*
* type: 1 - E_ERROR
* message: Call to undefined function undefinedFunc()
* line: 29
*/
?>

Answer 5

There is no errno. It is not needed, as you cannot handle errors properly in PHP anyway.
Note that error_get_last() (needs PHP 5.2 or above) is no proper replacement for something like errno as this error_get_last() is a security nightmare. It exposes PHP internals to the public if you ever output parts of this information. From a security point of view any such leaked information then is a major security incident and should be reported to the CERT of the organization for immediate mitigation.
Example:
fsockopen("unix://sock")
There is a very big difference which error can happen, so perhaps you want to inform your users about several possible states, so they know whom to call to fix the error. Do not do that. Do not even think about doing that!
There is no way to tell easily which error occurred, as this information is deeply buried in error_get_last() and there is hardly no way to handle it properly in any situation:
Example output (JSON):
{"type":2
,"message":"fsockopen(): unable to connect to unix://sock:-1 (Connection refused)"
,"file":"/var/www/html/test.php"
,"line":3
}
which means, the application probably is not running and you should contact application support. However
{"type":2
,"message":"fsockopen(): unable to connect to unix://sock:-1 (No such file or directory)"
,"file":"/var/www/html/test.php"
,"line":3
}
probably means, something wasn't correctly deployed, so you probably must contact the devs to fix the deployment. But with
{"type":2
,"message":"fsockopen(): unable to connect to unix://sock:-1 (Permission denied)"
,"file":"/var/www/html/test.php"
,"line":3
}
you have a sign for some configuration problem, which probably must be fixed by the Operators of the web service.
But do not fall into the trap and trust the output of this function, as there can be something like this:
{"type":2
,"message":"fsockopen(): unable to connect to unix://sock:-1 (basic shuttle outflop)\n:-1 (No such file or directory)",
,"file":"/var/www/html/test.php"
,"line":3
}
This, for example, could stem from some hacking going on, where someone successfully managed to replace the socket name to read "sock:-1 (basic shuttle outflop)\n" hence showing the hacker, that he successfully injected some code.
Read:
Exposing the message, even only partly, is a very bad thing. The bar to handle this properly is beyond infinity, so it must not be used to decide what to do, else your application might leak sensitive internals to some attacking party.
TL;DR
With PHP there is no way to properly handle different error conditions differently. Period.
With PHP there are only 2 states: OK and ERR (which is anything not 100% OK)
Always handle all errors the same, regardless of the type of error:
On any error, let the PHP-application die() immediately. Everything else would be insecure as hell.
Instead of handling errors afterwards, work around possible errors before they can hit the PHP code, so errors never occur in the normal program flow.
Then you never need something like errno, resulting in PHP code which might do something reasonable on typical error situations:
If any (intern or extern) error hits the PHP code, the code terminates with a fatal notifying you. As if some error condition was forgot, this means the code has a bug.
All other error conditions are handled before they can happen, hence you always have a program flow which is independent from errors, as no errors can hit that code.
Also note that E_WARNING must be handled as error, too. Else you risk insecurities with PHP, because many security related problems just show up as a warning.
Of course you can try to ignore this all. But this means you are living dangerously. If this code is published or is accessible publicly as a service, you endanger others.