New extender for error handling

This extender implements several methods for extending the new error
handling stack implemented in #1843.

Most use-cases should be covered, but I expect some challenges for more
complex setups. We can tackle those once they come up, though. Basic
use-cases should be covered.

Fixes #1781.

src/Extend/ErrorHandling.php

@@ -0,0 +1,120 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * For detailed copyright and license information, please view the
+ * LICENSE file that was distributed with this source code.
+ */
+
+namespace Flarum\Extend;
+
+use Flarum\Extension\Extension;
+use Flarum\Foundation\ErrorHandling\Reporter;
+use Illuminate\Contracts\Container\Container;
+
+class ErrorHandling implements ExtenderInterface
+{
+    private $statuses = [];
+    private $types = [];
+    private $handlers = [];
+    private $reporters = [];
+
+    /**
+     * Define the corresponding HTTP status code for a well-known error type.
+     *
+     * This can be used to configure the status code (second parameter) to be
+     * used for the error response when encountering an exception with a certain
+     * type (first parameter). This type can be provided by the exception class
+     * itself (if it implements {@see \Flarum\Foundation\KnownError}), or
+     * explicitly defined by using the {@see type} method (useful for exception
+     * classes not under your control).
+     */
+    public function status(string $errorType, int $httpStatus)
+    {
+        $this->statuses[$errorType] = $httpStatus;
+
+        return $this;
+    }
+
+    /**
+     * Define the internal error type for a specific exception class.
+     *
+     * If the exception class is under your control, you should prefer having
+     * the exception implement our {@see \Flarum\Fondation\KnownError} interface
+     * and define the type there. This method should only be used for third-
+     * party exceptions, e.g. when integrating another package that already
+     * defines its own exception classes.
+     */
+    public function type(string $exceptionClass, string $errorType)
+    {
+        $this->types[$exceptionClass] = $errorType;
+
+        return $this;
+    }
+
+    /**
+     * Register a handler with custom error handling logic.
+     *
+     * When Flarum's default error handling is not enough for you, and the other
+     * methods of this extender don't help, this is the place where you can go
+     * wild! Using this method, you can define a handler class (second
+     * parameter) that will be responsible for exceptions of a certain type
+     * (first parameter).
+     *
+     * The handler class must implement a handle() method (surprise!), which
+     * returns a {@see \Flarum\Foundation\ErrorHandling\HandledError} instance.
+     * Besides the usual type and HTTP status code, such an object can also
+     * contain "details" - arbitrary data with more context for to the error.
+     */
+    public function handler(string $exceptionClass, string $handlerClass)
+    {
+        $this->handlers[$exceptionClass] = $handlerClass;
+
+        return $this;
+    }
+
+    /**
+     * Register an error reporter.
+     *
+     * Reporters will be called whenever Flarum encounters an exception that it
+     * does not know how to handle (i.e. none of the well-known exceptions that
+     * have an associated error type). They can then e.g. write the exception to
+     * a log, or send it to some external service, so that developers and/or
+     * administrators are notified about the error.
+     *
+     * When passing in a reporter class, make sure that it implements the
+     * {@see \Flarum\Foundation\ErrorHandling\Reporter} interface.
+     */
+    public function reporter(string $reporterClass)
+    {
+        $this->reporters[] = $reporterClass;
+
+        return $this;
+    }
+
+    public function extend(Container $container, Extension $extension = null)
+    {
+        if (count($this->statuses)) {
+            $container->extend('flarum.error.statuses', function ($statuses) {
+                return array_merge($statuses, $this->statuses);
+            });
+        }
+
+        if (count($this->types)) {
+            $container->extend('flarum.error.classes', function ($types) {
+                return array_merge($types, $this->types);
+            });
+        }
+
+        if (count($this->handlers)) {
+            $container->extend('flarum.error.handlers', function ($handlers) {
+                return array_merge($handlers, $this->handlers);
+            });
+        }
+
+        foreach ($this->reporters as $reporterClass) {
+            $container->tag($reporterClass, Reporter::class);
+        }
+    }
+}