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[Debug][ErrorHandler] Preserve our error handler when a logger sets another one #29869

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merged 1 commit into from Jan 25, 2019

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fancyweb commented Jan 13, 2019

Q A
Branch? 3.4
Bug fix? yes
New feature? no
BC breaks? no
Deprecations? no
Tests pass? yes
Fixed tickets -
License MIT
Doc PR -

When logging errors handled by the ErrorHandler::handleError() method, the logger can temporarily set its own custom error handler. This is for example the case of Monolog in the StreamHandler class (cf https://github.com/Seldaek/monolog/blob/ebb804e432e8fe0fe96828f30d89c45581d36d07/src/Monolog/Handler/StreamHandler.php#L101).

However, when the previous error handler is restored by the logger, it "skips" the real previous handler (the ErrorHandler::handleError() one) in the pile and goes back directly to the one before. I guess this is because the restore_error_handler() call is technically done in the error handler itself, so it logically restore it to the one before and not to itself.

Here is an easy small example that shows the PHP behavior : https://3v4l.org/4OZNZ

The only solution I have found to fix it is to set our error handler everytime an error is logged.

Here are the things I discovered while trying to find a cleaner fix :

  • Setting the same error handler in the error handler itself doesn't actually add it to the pile. This is why adding a check is useless.
  • Checking if the logger modified the error handler is impossible anyway : to get the current error handler, you need to set a new one temporarirly and then revert it. However, when you revert it by calling restore_error_handler() you end up having the same problem you are trying to fix...
  • Also trying to get the current error handler in the error handler itself will return NULL if it is itself.

@fancyweb fancyweb changed the title [Debug][ErrorHandler] Preserve our error handler when a logger set another one [Debug][ErrorHandler] Preserve our error handler when a logger sets another one Jan 13, 2019

@fancyweb fancyweb force-pushed the fancyweb:always-preserve-error-handler-when-logging branch 2 times, most recently from 2c73341 to 6af95d4 Jan 17, 2019

@nicolas-grekas nicolas-grekas added this to the 3.4 milestone Jan 24, 2019

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nicolas-grekas commented Jan 24, 2019

Nice finding, LGTM. Could you please have a look at HHVM tests, are they related? (rebasing and checking other PRs on 3.4 might help decide).

@fancyweb fancyweb force-pushed the fancyweb:always-preserve-error-handler-when-logging branch from 6af95d4 to a40a292 Jan 24, 2019

@fancyweb fancyweb force-pushed the fancyweb:always-preserve-error-handler-when-logging branch from a40a292 to b979fff Jan 24, 2019

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fancyweb commented Jan 24, 2019

Failures were actually related.

Turns out this bug does not exist on the tested HHVM version so we must not readd the error handler.

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nicolas-grekas commented Jan 25, 2019

Good catch, thanks @fancyweb.

@nicolas-grekas nicolas-grekas merged commit b979fff into symfony:3.4 Jan 25, 2019

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nicolas-grekas added a commit that referenced this pull request Jan 25, 2019

bug #29869 [Debug][ErrorHandler] Preserve our error handler when a lo…
…gger sets another one (fancyweb)

This PR was merged into the 3.4 branch.

Discussion
----------

[Debug][ErrorHandler] Preserve our error handler when a logger sets another one

| Q             | A
| ------------- | ---
| Branch?       | 3.4
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

When logging errors handled by the `ErrorHandler::handleError()` method, the logger can temporarily set its own custom error handler. This is for example the case of `Monolog` in the `StreamHandler` class (cf https://github.com/Seldaek/monolog/blob/ebb804e432e8fe0fe96828f30d89c45581d36d07/src/Monolog/Handler/StreamHandler.php#L101).

However, when the previous error handler is restored by the logger, it "skips" the real previous handler (the `ErrorHandler::handleError()` one) in the pile and goes back directly to the one before. I guess this is because the `restore_error_handler()` call is technically done in the error handler itself, so it logically restore it to the one before and not to itself.

Here is an easy small example that shows the PHP behavior : https://3v4l.org/4OZNZ

The only solution I have found to fix it is to set our error handler everytime an error is logged.

Here are the things I discovered while trying to find a cleaner fix :
- Setting the same error handler in the error handler itself doesn't actually add it to the pile. This is why adding a check is useless.
- Checking if the logger modified the error handler is impossible anyway : to get the current error handler, you need to set a new one temporarirly and then revert it. However, when you revert it by calling `restore_error_handler()` you end up having the same problem you are trying to fix...
- Also trying to get the current error handler in the error handler itself will return NULL if it is itself.

Commits
-------

b979fff [Debug][ErrorHandler] Preserve our error handler when a logger set another one

This was referenced Jan 29, 2019

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