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Request for Comments: Enhanced Error Handling


php_error(), zend_throw_extension(), the @-operator… PHP and/or the Zend Engine respectively offer a variety of error issuance and handling mechanisms. There is, however, no encompassing concepts: Core functions only issue php_errors (suppressable), intl 1.0.3 by default suppresses all errors but can activate php_errors, pdo however has a flag to define error behaviour that allows exceptions - but limits php_error to E_WARNING. Furthermore, each extension has a different way of changing its error behaviour.

I think that error behaviour has to be in the hands of the user (php coder). Different users have different preferences - and prefer different behaviour in different situations.


Error conditions are encountered in a variety of places and cases. This RFC only covers error conditions in a running script, e.g. a file was not found.

All other situations - like compilation problems, core errors in engine startup/shutdown - are out of scope.


Error Behaviours

If an error condition is met, different types of reactions are possible:

Name Description
Suppress Note down error and return an error value, e.g. false/NULL
Monitor same as Suppress, but let a php monitor know - independent of error handling taken by user code
Error same as Suppress, but issue a php_error as well
Throw same as Suppress, but throw an exception as well

The error behaviour should be configurable by the user. An extension should not differ from the user's wishes, except in absolutely extraordinary circumstances.

Noted-down error information, e.g. error code and message etc., should be available by a standardized API.

Error Parameters

Different behaviours, ask for different additional parameters: zend_error needs an E_* value to distinguish warnings and errors and throwing an exception needs an exception class.

Default values for those parameters should be configurable like the error behaviour. However, more specific values - like an BadFunctionCallException while testing parameters - have to be definable with the error call itself.

For extreme cases - like “one big exception block per script” - the default parameters should be enforcable by the user.

Error Container Hierarchy

PHP lives of its extensibility. Different extensions currently show different default error behaviours. It goes without saying, that error behaviour must keep being configurable by extension.

As some extensions currently do, I propose to add a further layer of error configurability on object level (see e.g. PDO → by PDO connection). They should default to the extension's behaviour, but be configurable differently.

Special Cases

Enforced Exception class

A lower hierarchy level could enforce the use of a specific exception class, e.g. PersonalIntlExceptionClass() for all of intl.so. While forcing such a common class does ease catching, some information a more specific class could provide is lost.

As of PHP 5.3, the concept of exception chaining has been introduced, whereas a “previous” extension can be attached. In order to keep the previously lost information, the concrete exception class given upon issuing an error should be chained to the enforced class.


Notices are issued en masse all over PHP - even for plain language constructs like array access. They are regularly ignored on production systems and seldomly indicate errors. I like to compare them to warnings of a compiler, indicating that something could go wrong here (php does issue them at runtime, not compile-time).

Whereas an user could decide to downgrade every error to a notice in this concept, actual notices should be issued the same way as before.


The @ operator does suppress error issuance for the evaluation of the expression it is prepended to. It does so - currently - completely for php_error()s, not however for exceptions.

If possible, the operator should be limited to errors in the execution of scripts but “silence” thrown exceptions as well (like a “per object” Suppress above). It's functionality should be prohibited, if a certain behaviour is enforced.


The following does not represent compilable code.

Error Container

The levels mentioned above would need a common container structure to hold error configuration as well as “last error” information. The same construct can be hold by extensions as well as objects.

  struct error_container {
    char *name;                         // identification, e.g. extension name
    error_container *parent;            // hierarchy: inherit parent's configuration
    error_container *delegate;          // hierarchy: "last" error is in a child from this one
    error_behaviour  behaviour;         // error behaviour for this container
    long             level;             // default E_*
    zend_class_entry *exception;        // default exception class
    error_incident incident;            // last error's information on this container's level

Error Function

  error_behaviour error_yell( error_container *container, long level, char *exception, long code, char *msg );
  error_behaviour error_yellf( error_container *container, long level, char *exception, long code, char *format, ... );

Instead of writing explicit calls to zend_error or zend_exception_throw, this call abstracts away the error behaviour. It does, however return the actual behaviour initiated.

As errors might be suppressed, after the use of error_yell a defined return value should be returned to PHP. One cannot be sure that the engine will branch away into an error or exception handler.

Utility functions

Apart from the error issuing function, several utility functions are needed, e.g.:

  • Creation/Destruction of error containers
  • Setting/Resetting error behaviour of containers
  • Reading error incidents
  • Clearing error incidents

The corresponding API depends too much on implementation detais to discuss those here.


Apart from extensions in C, php code itself could use such unified error configuration as well. Above mentioned error_yell function as well as utility functions to configure error behaviour and read error information should be available.

A standard ErrorClass - implementing an object level error container plus standardized methods to access it - should be available:

  class ErrorClass {
    function __construct( $parent_container )
    function setErrorBehaviour(...);
    function resetErrorBehaviour();
    function yellError(...);
    function getLastError();

Of course, the internal ErrorClass could be used as base class for extension classes as well.

Error containers would be identified by:

  • NULL: global/highest hierarchy
  • string: extension-level container (e.g. in a hash)
  • ErrorClass: object-level container

In order to allow PHP frameworks to depend on an “extension level” container, such a string-identified container should be creatable on user level.

Backwards Compatibility


Extensions can keep backwards compatibility, if their current default behaviour is mapped to the above-mentioned extension level. Even special cases should be representable with the mentioned behaviours, parameters and enforcement.


The core should probably only be touched if this proposal (or something analogous) is included in it…

Course of Action and Patch

  1. Given enough feedback and operating experience, the enhanced error handling could be bundled in an “error extension”
  2. Other extensions could use the “error extension”


Date Author Message
2009-12-27 kampfcaspar Created Initial Version
2009-12-28 kampfcaspar Added draft API
2010-01-07 kampfcaspar Overhaul
rfc/enhanced_error_handling.1262879581.txt.gz · Last modified: 2017/09/22 13:28 (external edit)