Merge pull request #249 from clue-labs/set-rejection-handler

Add new `set_rejection_handler()` function for unhandled rejections

Author: WyriHaximus

README.md

@@ -41,6 +41,7 @@ Table of Contents
      * [all()](#all)
      * [race()](#race)
      * [any()](#any)
+     * [set_rejection_handler()](#set-rejection-handler)
 4. [Examples](#examples)
    * [How to use Deferred](#how-to-use-deferred)
    * [How promise forwarding works](#how-promise-forwarding-works)
@@ -437,6 +438,8 @@ A rejected promise will also be considered "handled" if you abort the operation
 with the [`cancel()` method](#promiseinterfacecancel) (which in turn would
 usually reject the promise if it is still pending).
 
+See also the [`set_rejection_handler()` function](#set-rejection-handler).
+
 #### all()
 
 ```php
@@ -478,6 +481,46 @@ which holds all rejection reasons. The rejection reasons can be obtained with
 The returned promise will also reject with a `React\Promise\Exception\LengthException`
 if `$promisesOrValues` contains 0 items.
 
+#### set_rejection_handler()
+
+```php
+React\Promise\set_rejection_handler(?callable $callback): ?callable;
+```
+
+Sets the global rejection handler for unhandled promise rejections.
+
+Note that rejected promises should always be handled similar to how any
+exceptions should always be caught in a `try` + `catch` block. If you remove
+the last reference to a rejected promise that has not been handled, it will
+report an unhandled promise rejection. See also the [`reject()` function](#reject)
+for more details.
+
+The `?callable $callback` argument MUST be a valid callback function that
+accepts a single `Throwable` argument or a `null` value to restore the
+default promise rejection handler. The return value of the callback function
+will be ignored and has no effect, so you SHOULD return a `void` value. The
+callback function MUST NOT throw or the program will be terminated with a
+fatal error.
+
+The function returns the previous rejection handler or `null` if using the
+default promise rejection handler.
+
+The default promise rejection handler will log an error message plus its stack
+trace:
+
+```php
+// Unhandled promise rejection with RuntimeException: Unhandled in example.php:2
+React\Promise\reject(new RuntimeException('Unhandled'));
+```
+
+The promise rejection handler may be used to use customize the log message or
+write to custom log targets. As a rule of thumb, this function should only be
+used as a last resort and promise rejections are best handled with either the
+[`then()` method](#promiseinterfacethen), the
+[`catch()` method](#promiseinterfacecatch), or the
+[`finally()` method](#promiseinterfacefinally).
+See also the [`reject()` function](#reject) for more details.
+
 Examples
 --------
 

src/Internal/RejectedPromise.php

@@ -5,6 +5,7 @@
 use React\Promise\PromiseInterface;
 use function React\Promise\_checkTypehint;
 use function React\Promise\resolve;
+use function React\Promise\set_rejection_handler;
 
 /**
  * @internal
@@ -25,16 +26,31 @@ public function __construct(\Throwable $reason)
         $this->reason = $reason;
     }
 
+    /** @throws void */
     public function __destruct()
     {
         if ($this->handled) {
             return;
         }
 
-        $message = 'Unhandled promise rejection with ' . \get_class($this->reason) . ': ' . $this->reason->getMessage() . ' in ' . $this->reason->getFile() . ':' . $this->reason->getLine() . PHP_EOL;
-        $message .= 'Stack trace:' . PHP_EOL . $this->reason->getTraceAsString();
+        $handler = set_rejection_handler(null);
+        if ($handler === null) {
+            $message = 'Unhandled promise rejection with ' . \get_class($this->reason) . ': ' . $this->reason->getMessage() . ' in ' . $this->reason->getFile() . ':' . $this->reason->getLine() . PHP_EOL;
+            $message .= 'Stack trace:' . PHP_EOL . $this->reason->getTraceAsString();
 
-        \error_log($message);
+            \error_log($message);
+            return;
+        }
+
+        try {
+            $handler($this->reason);
+        } catch (\Throwable $e) {
+            $message = 'Fatal error: Uncaught ' . \get_class($e) . ' from unhandled promise rejection handler: ' . $e->getMessage() . ' in ' . $e->getFile() . ':' . $e->getLine() . PHP_EOL;
+            $message .= 'Stack trace:' . PHP_EOL . $e->getTraceAsString();
+
+            \error_log($message);
+            exit(255);
+        }
     }
 
     public function then(callable $onFulfilled = null, callable $onRejected = null): PromiseInterface

src/functions.php

@@ -206,6 +206,53 @@ function (\Throwable $reason) use ($i, &$reasons, &$toReject, $reject, &$continu
     }, $cancellationQueue);
 }
 
+/**
+ * Sets the global rejection handler for unhandled promise rejections.
+ *
+ * Note that rejected promises should always be handled similar to how any
+ * exceptions should always be caught in a `try` + `catch` block. If you remove
+ * the last reference to a rejected promise that has not been handled, it will
+ * report an unhandled promise rejection. See also the [`reject()` function](#reject)
+ * for more details.
+ *
+ * The `?callable $callback` argument MUST be a valid callback function that
+ * accepts a single `Throwable` argument or a `null` value to restore the
+ * default promise rejection handler. The return value of the callback function
+ * will be ignored and has no effect, so you SHOULD return a `void` value. The
+ * callback function MUST NOT throw or the program will be terminated with a
+ * fatal error.
+ *
+ * The function returns the previous rejection handler or `null` if using the
+ * default promise rejection handler.
+ *
+ * The default promise rejection handler will log an error message plus its
+ * stack trace:
+ *
+ * ```php
+ * // Unhandled promise rejection with RuntimeException: Unhandled in example.php:2
+ * React\Promise\reject(new RuntimeException('Unhandled'));
+ * ```
+ *
+ * The promise rejection handler may be used to use customize the log message or
+ * write to custom log targets. As a rule of thumb, this function should only be
+ * used as a last resort and promise rejections are best handled with either the
+ * [`then()` method](#promiseinterfacethen), the
+ * [`catch()` method](#promiseinterfacecatch), or the
+ * [`finally()` method](#promiseinterfacefinally).
+ * See also the [`reject()` function](#reject) for more details.
+ *
+ * @param callable(\Throwable):void|null $callback
+ * @return callable(\Throwable):void|null
+ */
+function set_rejection_handler(?callable $callback): ?callable
+{
+    static $current = null;
+    $previous = $current;
+    $current = $callback;
+
+    return $previous;
+}
+
 /**
  * @internal
  */

tests/FunctionSetRejectionHandlerShouldBeInvokedForUnhandled.phpt

@@ -0,0 +1,25 @@
+--TEST--
+The callback given to set_rejection_handler() should be invoked for unhandled rejection
+--INI--
+# suppress legacy PHPUnit 7 warning for Xdebug 3
+xdebug.default_enable=
+--FILE--
+<?php
+
+use function React\Promise\reject;
+use function React\Promise\set_rejection_handler;
+
+require __DIR__ . '/../vendor/autoload.php';
+
+set_rejection_handler(function (Throwable $e): void {
+    echo 'Unhandled ' . get_class($e) . ': ' . $e->getMessage() . PHP_EOL;
+});
+
+reject(new RuntimeException('foo'));
+
+echo 'done' . PHP_EOL;
+
+?>
+--EXPECT--
+Unhandled RuntimeException: foo
+done

tests/FunctionSetRejectionHandlerShouldInvokeLastHandlerForUnhandled.phpt

@@ -0,0 +1,37 @@
+--TEST--
+The callback given to the last set_rejection_handler() should be invoked for unhandled rejection
+--INI--
+# suppress legacy PHPUnit 7 warning for Xdebug 3
+xdebug.default_enable=
+--FILE--
+<?php
+
+use function React\Promise\reject;
+use function React\Promise\set_rejection_handler;
+
+require __DIR__ . '/../vendor/autoload.php';
+
+$ret = set_rejection_handler($first = function (Throwable $e): void {
+    echo 'THIS WILL NEVER BE CALLED' . PHP_EOL;
+});
+
+// previous should be null
+var_dump($ret === null);
+
+$ret = set_rejection_handler(function (Throwable $e): void {
+    echo 'Unhandled ' . get_class($e) . ': ' . $e->getMessage() . PHP_EOL;
+});
+
+// previous rejection handler should be first rejection handler callback
+var_dump($ret === $first);
+
+reject(new RuntimeException('foo'));
+
+echo 'done' . PHP_EOL;
+
+?>
+--EXPECT--
+bool(true)
+bool(true)
+Unhandled RuntimeException: foo
+done

tests/FunctionSetRejectionHandlerThatHasUnhandledShouldReportUnhandled.phpt

@@ -0,0 +1,30 @@
+--TEST--
+The callback given to set_rejection_handler() should be invoked for outer unhandled rejection but should use default rejection handler for unhandled rejection
+--INI--
+# suppress legacy PHPUnit 7 warning for Xdebug 3
+xdebug.default_enable=
+--FILE--
+<?php
+
+use function React\Promise\reject;
+use function React\Promise\set_rejection_handler;
+
+require __DIR__ . '/../vendor/autoload.php';
+
+set_rejection_handler(function (Throwable $e): void {
+    reject(new \UnexpectedValueException('bar'));
+
+    echo 'Unhandled ' . get_class($e) . ': ' . $e->getMessage() . PHP_EOL;
+});
+
+reject(new RuntimeException('foo'));
+
+echo 'done' . PHP_EOL;
+
+?>
+--EXPECTF--
+Unhandled promise rejection with UnexpectedValueException: bar in %s:%d
+Stack trace:
+#0 %A{main}
+Unhandled RuntimeException: foo
+done

tests/FunctionSetRejectionHandlerThatThrowsShouldTerminateProgramForUnhandled.phpt

@@ -0,0 +1,26 @@
+--TEST--
+The callback given to set_rejection_handler() should not throw an exception or the program should terminate for unhandled rejection
+--INI--
+# suppress legacy PHPUnit 7 warning for Xdebug 3
+xdebug.default_enable=
+--FILE--
+<?php
+
+use function React\Promise\reject;
+use function React\Promise\set_rejection_handler;
+
+require __DIR__ . '/../vendor/autoload.php';
+
+set_rejection_handler(function (Throwable $e): void {
+    throw new \UnexpectedValueException('This function should never throw');
+});
+
+reject(new RuntimeException('foo'));
+
+echo 'NEVER';
+
+?>
+--EXPECTF--
+Fatal error: Uncaught UnexpectedValueException from unhandled promise rejection handler: This function should never throw in %s:%d
+Stack trace:
+#0 %A{main}

tests/FunctionSetRejectionHandlerThatTriggersDefaultHandlerShouldTerminateProgramForUnhandled.phpt

@@ -0,0 +1,24 @@
+--TEST--
+The callback given to set_rejection_handler() may trigger a fatal error for unhandled rejection
+--INI--
+# suppress legacy PHPUnit 7 warning for Xdebug 3
+xdebug.default_enable=
+--FILE--
+<?php
+
+use function React\Promise\reject;
+use function React\Promise\set_rejection_handler;
+
+require __DIR__ . '/../vendor/autoload.php';
+
+set_rejection_handler(function (Throwable $e): void {
+    trigger_error('Unexpected ' . get_class($e) . ': ' .$e->getMessage(), E_USER_ERROR);
+});
+
+reject(new RuntimeException('foo'));
+
+echo 'NEVER';
+
+?>
+--EXPECTF--
+Fatal error: Unexpected RuntimeException: foo in %s line %d

tests/FunctionSetRejectionHandlerThatTriggersErrorHandlerThatThrowsShouldTerminateProgramForUnhandled.phpt

@@ -0,0 +1,35 @@
+--TEST--
+The callback given to set_rejection_handler() may trigger a fatal error which in turn throws an exception which will terminate the program for unhandled rejection
+--INI--
+# suppress legacy PHPUnit 7 warning for Xdebug 3
+xdebug.default_enable=
+--FILE--
+<?php
+
+use function React\Promise\reject;
+use function React\Promise\set_rejection_handler;
+
+require __DIR__ . '/../vendor/autoload.php';
+
+set_error_handler(function (int $_, string $errstr): void {
+    throw new \OverflowException('This function should never throw');
+});
+
+set_rejection_handler(function (Throwable $e): void {
+    trigger_error($e->getMessage(), E_USER_ERROR);
+});
+
+reject(new RuntimeException('foo'));
+
+echo 'NEVER';
+
+?>
+--EXPECTF--
+Fatal error: Uncaught OverflowException from unhandled promise rejection handler: This function should never throw in %s:%d
+Stack trace:
+#0 [internal function]: {closure}(%S)
+#1 %s(%d): trigger_error(%S)
+#2 %s/src/Internal/RejectedPromise.php(%d): {closure}(%S)
+#3 %s/src/functions.php(%d): React\Promise\Internal\RejectedPromise->__destruct()
+#4 %s(%d): React\Promise\reject(%S)
+#5 %A{main}

tests/FunctionSetRejectionHandlerThatUsesNestedSetRejectionHandlerShouldInvokeInnerHandlerForUnhandled.phpt

@@ -0,0 +1,36 @@
+--TEST--
+The callback given to set_rejection_handler() should be invoked for outer unhandled rejection and may set new rejection handler for inner unhandled rejection
+--INI--
+# suppress legacy PHPUnit 7 warning for Xdebug 3
+xdebug.default_enable=
+--FILE--
+<?php
+
+use function React\Promise\reject;
+use function React\Promise\set_rejection_handler;
+
+require __DIR__ . '/../vendor/autoload.php';
+
+set_rejection_handler(function (Throwable $e): void {
+    $ret = set_rejection_handler(function (Throwable $e): void {
+        echo 'Unhandled inner ' . get_class($e) . ': ' . $e->getMessage() . PHP_EOL;
+    });
+
+    // previous rejection handler should be unset while handling a rejection
+    var_dump($ret === null);
+
+    reject(new \UnexpectedValueException('bar'));
+
+    echo 'Unhandled outer ' . get_class($e) . ': ' . $e->getMessage() . PHP_EOL;
+});
+
+reject(new RuntimeException('foo'));
+
+echo 'done' . PHP_EOL;
+
+?>
+--EXPECT--
+bool(true)
+Unhandled inner UnexpectedValueException: bar
+Unhandled outer RuntimeException: foo
+done