Explore PHP values, exceptions and call stacks in plain text and interactive HTML
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fail-whale is a system for introspecting PHP values and exceptions and rendering them in plain text and interactive HTML.


Install the Composer package



use FailWhale\Value;

class Foo {
    private $baz = "bar";
    protected $an_int = 967;
    public $an_array = [
        'baz' => [
            8346 => 762.192,
            'key1' => "string with\nnew lines\n\t\tand\r\n\ttabs\nand a CR",
            'key2' => "random bytes \xc4\x08\x12\xb1",
            'key3' => M_PI,
            'key4' => null,
            'key6' => true,
    private $bar;

    function __construct() {
        $this->bar = new Bar();
        $baz =& $this->an_array['baz'];
        $baz['recurse'] =& $baz;
        $baz['stream'] = fopen('php://memory', 'wb');

class Bar {
    private $copies;
    function __construct() {
        $this->copies = [$this, $this];

print Value::introspect(new Foo)->toString();
new Foo {
    private $baz = "bar";
    protected $an_int = 967;
    public $an_array = array(
        "baz" => &array002 array(
            8346 => 762.192,
            "key1" => "string with
new lines
and a CR",
            "key2" => "random bytes \xc4\x08\x12\xb1",
            "key3" => 3.1415926535898,
            "key4" => null,
            "key6" => true,
            "recurse" => *array002,
            "stream" => stream,
    private $bar = &object002 new Bar {
        private $copies = array(
            *object002 new Bar,
            *object002 new Bar,

A Value can represent an Exception or a single PHP value.

Value::introspect(), Value::introspectRef(), Value::introspectException()

Value::introspect() and Value::introspectRef() will handle arbitrary PHP values, including recursive arrays (eg $a = [&$a]) and recursive objects.

Value::introspectException() will handle any Exception and retrieve:

  • it's code, message, file and line
  • a full stack trace, including function name, class name, arguments, $this, file and line
  • the entire global state of the PHP program
    • global variables
    • static class properties
    • static variables
  • if it is a ErrorExceptionWithContext, the local variables ("context") at the point that the PHP error occurred
  • the source code which surrounds the line where the exception was thrown and the surrounding code for each function call on the stack

All Value::introspect*() methods optionally accept a IntrospectionSettings object.

Value::toJSON(), Value::fromJSON()

Value->toJSON() will return a JSON string suitable for Value::fromJSON().

Value::toHTML(), Value::toInlineHTML()

Value->toHTML() will return a full HTML document which represents the value in a browsable, expandable/collapsible form.

Value->toInlineHTML() will return HTML suitable for embedding in another HTML document.


Value->toString() will pretty-print the value as a string. It optionally accepts a PrettyPrinterSettings object to control how the value is rendered.

PHP values (and exceptions) containing repeated arrays, objects and strings are handled gracefully, as are recursive arrays and objects.

Scalar values (int, string, bool, float, null) and non-recursive arrays are rendered as valid PHP code.

Error Handler

ErrorUtil::setExceptionTrace(), ExceptionWithTraceObjects

In order to see the $this object (current object) for each stack frame in an exception, you should overwrite the default trace for an exception with one provided by debug_backtrace() using ErrorUtil::setExceptionTrace():

use FailWhale\ErrorUtil;

$e = new Exception('oh no!');
ErrorUtil::setExceptionTrace($e, debug_backtrace());
throw $e;

It is more convenient to do this in the constructor of your exception:

use FailWhale\ErrorUtil;

class BadException {
    function __construct($message) {
        ErrorUtil::setExceptionTrace($this, debug_backtrace());

throw new BadException('oh no!');

Or you could instantiate or extend ExceptionWithTraceObjects which will do this for you:

use FailWhale\ExceptionWithTraceObjects;

throw new ExceptionWithTraceObjects('oh no!');

ErrorUtil::setExceptionTrace() uses reflection to set the private property Exception::$trace, which is returned by $e->getTrace(). Try not to think about that too much. ;)

You can also use ErrorUtil::setExceptionTrace() to remove the top stack frame from an exception, to avoid your error handler appearing in the trace, for example.

use FailWhale\ErrorUtil;

set_error_handler(function ($type, $message, $file, $line, $context = null) {
    $e = new ErrorException($message, 0, $type, $file, $line);
    ErrorUtil::setExceptionTrace($e, array_slice($e->getTrace(), 1)); // <=
    throw $e;


In order to see the local variables for PHP errors, you should use ErrorExceptionWithContext in place of ErrorException in your error handler, and call $e->setContext() with the $context array provided to your error handler from set_error_handler(). For example:

use FailWhale\ErrorExceptionWithContext;

set_error_handler(function ($type, $message, $file, $line, $context = null) {
    $e = new ErrorExceptionWithContext($message, 0, $type, $file, $line);
    $e->setContext($context); // <=
    throw $e;

ErrorUtil::phpErrorConstant(), ErrorUtil::phpErrorName()

For a given PHP error type, ErrorUtil::phpErrorConstant() and ErrorUtil::phpErrorName() will return the name of the constant and descriptive name respectively.

use FailWhale\ErrorUtil;

print ErrorUtil::phpErrorConstant(E_PARSE); // E_PARSE
print ErrorUtil::phpErrorName(E_PARSE); // Parse Error

This can be useful for setting the code (as opposed to the severity/level/type) for an ErrorException, which is usually set to 0. Since new ErrorException(...) only accepts integers for $code, you should use ErrorExceptionWithContext instead and call setCode(). For example:

use FailWhale\ErrorExceptionWithContext;
use FailWhale\ErrorUtil;

set_error_handler(function ($type, $message, $file, $line, $context = null) {
    $e = new ErrorException($message, 0, $type, $file, $line);
    $e->setCode(ErrorUtil::phpErrorConstant($type)); // <=
    throw $e;


ErrorUtil::setErrorAndExceptionHandler() provides a PHP error handler which does all of the above for you, in addition to handling fatal errors. You are welcome to use that:

use FailWhale\ErrorUtil;

ErrorUtil::setErrorAndExceptionHandler(function (Exception $e) {
    if ($e instanceof ErrorException)
        print "A PHP error occurred!\n";
        print "An exception occurred!\n";

    print $e->getMessage();

Error Handler + Pretty Printer

Putting these two pieces together, an error handler which prints a interactive HTML version of an exception to the browser might look like this:

use FailWhale\ErrorUtil;
use FailWhale\Value;

ErrorUtil::setErrorAndExceptionHandler(function (Exception $e) {
    $value = Value::introspectException($e);

    if (PHP_SAPI === 'cli')
        print $value->toString();
        print $value->toHTML();