PHP resources cannot be identified from backtrace (call stack) - php

Question

I'm writing PHP method to pretty-print callstack with params. Reason for this is it will be used as an output of a public API (in debug mode) so it must not display everything and only display save information.
I would like to see something like this:
Config->saveToFile(resource: file) in config.php::456
Config->backup('config.bak') in config.php::123
But when I call debug_backtrace() and parse the args value, I cannot use methods gettype(), is_resource() and get_resource_type() because it always say the variable is of unknown type:
Config->saveToFile(Unknown type: Resource id #99) in config.php::456
Config->backup('config.bak') in config.php::123
Code used to parse args is:
public static function getTrace() {
$trace = debug_backtrace();
$output = [];
foreach ($trace as $call) {
$name = $call['class'] . $call['type'] . $call['function']
//actual code checks for various situations
$args = [];
foreach ($call['args'] as $arg) {
$args[] = self::toString($arg);
}
$name .= '(' . join(', ', $args) . ')';
$output[] = $name . ' in ' . basename($call['file']) . '::' . $call['line'];
}
return $output;
}
protected static function toString($mixed) {
//process known types - arrays, objects, strings, etc.
//...
if (is_resource($mixed)) {
return 'resource: ' . get_resource_type($mixed);
}
return gettype($mixed) . ': ' . $mixed;
}
Even when I use code by diz at ysagoon dot com listed under debug_backtrace documentation, which utilize gettype() and check for resource, in my case it returns Config->saveToFile(Unknown).
When I use the methods in code where the resource is created, it correctly returns its type.
Is there a limit or reason why resources are not identified from backtrace? Something I should enable in PHP configuration? I haven't found anything about this in PHP documentation nor Google.
System:
XAMPP 3.2.2
Apache/2.4.17 (Win32)
PHP/5.6.15
Windows 10 Pro x64 Anniversary edition 1607 (10.0.14393)

Answer 1

So the problem is that resources can be identified as a resource only while they are opened. After you close the resource, it is no more identified by methods gettype(), is_resource() and get_resource_type() as a resource and instead change to unknown type.
$f = fopen('tmp', 'w');
echo gettype($f); //= 'resource'
fclose($f);
echo gettype($f); //= 'Unknown type'
To print closed resources in backtrace I've created two methods to remember resources while they are still opened:
protected $resources = [];
public function traceResourceParams() {
$trace = debug_backtrace();
$args = [];
foreach ($trace as $call) {
foreach ($call['args'] as $arg) {
if (is_resource($arg) && !array_key_exists(intval($arg), $this->resources)) {
$this->resources[intval($arg)] = self::toString($arg);
}
}
}
}
public function traceNamedResource($resource, $name) {
if (is_resource($resource)) {
$this->resources[intval($resource)] = '{' . get_resource_type($resource) . ': ' . $name . '}';
}
}
And updated my toString method to check for stored resources:
protected static function toString($mixed) {
//process known types - arrays, objects, strings, etc.
//...
if (is_resource($mixed)) {
return 'resource: ' . get_resource_type($mixed);
}
//closed resources does not evaluate as resource
//but still convert to resource id using intval()
//so we can match them to previously evaluated resources
$val = intval($mixed);
if ($val && array_key_exists($val, self::getInstance()->resources)) {
return self::getInstance()->resources[$val];
}
return gettype($mixed) . ': ' . $mixed;
}
So now I can store the resource when it is created:
$f = fopen('tmp', 'w');
$debug->traceNamedResource($f, 'tmp');
fclose($f);
Or when it is passed as a parameter:
protected function saveToFile($file) {
$debug->traceResourceParams()
//... work with file
fclose($file);
}