Support for fatal errors on XML-RPC

[koke]

Similar to #16748, when a fatal error occurs, PHP will output some HTML code which at best is confusing for XML-RPC clients.

Using the shutdown action, we could die more gracefully and return a XML-RPC formatted error

[koke]

Not sure if the attached patch would be the best implementation, but it's a starting point

[sirzooro]

+1 for this.

PHP error should be reported in debug environment only - otherwise this is a potential security issue. Please check if WP_DEBUG is set to true; if not, return some generic error message like "WP internal error" instead.

[redsweater]

Very cool idea. I'm definitely excited by anything that would improve the verbosity of errors when connecting via XMLRPC.

sirzooro: Would it be possible to set this up so it reports the PHP error only when the XMLRPC client has authenticated? The vast majority of error-prone activity occurs only after the user has authenticated, where it would make sense to allow verbose error messages to be conveyed to the user through XMLRPC. In this case, I don't think it would be a security issue to pass that along, at least for most WordPress configurations. Perhaps it could be limited to specific user roles.

[beaucollins]

Similarly, perhaps we can have the ​wp_xmlrpc_server use ​set_error_handler to prevent all non-fatal errors from being dumped to stdout in the event that PHP is configured to report errors to STDOUT.

[SergeyBiryukov]

Related: #23811

[ocean90]

Fixed in [44973]/#44458.