Prevent infinite loops from zero-interval DatePeriods

Adds validation to ChronosPeriod and ChronosDatePeriod constructors
to throw an InvalidArgumentException when given a DatePeriod with a
zero interval (e.g., PT0S or P0D).

Without this check, iterating over such a period causes an infinite
loop that can crash the server.

Also fixes typo in ChronosDatePeriodTest (ChronosDAte -> ChronosDate).

Author: dereuromark

src/ChronosDatePeriod.php

@@ -14,7 +14,9 @@
 
 namespace Cake\Chronos;
 
+use DateInterval;
 use DatePeriod;
+use InvalidArgumentException;
 use Iterator;
 
 /**
@@ -32,15 +34,39 @@ class ChronosDatePeriod implements Iterator
     protected Iterator $iterator;
 
     /**
-     * @param \DatePeriod $period
+     * @param \DatePeriod $period The DatePeriod to wrap.
+     * @throws \InvalidArgumentException If the period has a zero interval which would cause an infinite loop.
      */
     public function __construct(DatePeriod $period)
     {
+        if (static::isZeroInterval($period->getDateInterval())) {
+            throw new InvalidArgumentException(
+                'Cannot create a period with a zero interval. This would cause an infinite loop when iterating.',
+            );
+        }
+
         /** @var \Iterator<int, \DateTimeInterface> $iterator */
         $iterator = $period->getIterator();
         $this->iterator = $iterator;
     }
 
+    /**
+     * Check if a DateInterval is effectively zero.
+     *
+     * @param \DateInterval $interval The interval to check.
+     * @return bool True if the interval is zero.
+     */
+    protected static function isZeroInterval(DateInterval $interval): bool
+    {
+        return $interval->y === 0
+            && $interval->m === 0
+            && $interval->d === 0
+            && $interval->h === 0
+            && $interval->i === 0
+            && $interval->s === 0
+            && (int)($interval->f * 1_000_000) === 0;
+    }
+
     /**
      * @return \Cake\Chronos\ChronosDate
      */

src/ChronosPeriod.php

@@ -14,7 +14,9 @@
 
 namespace Cake\Chronos;
 
+use DateInterval;
 use DatePeriod;
+use InvalidArgumentException;
 use Iterator;
 
 /**
@@ -32,15 +34,39 @@ class ChronosPeriod implements Iterator
     protected Iterator $iterator;
 
     /**
-     * @param \DatePeriod $period
+     * @param \DatePeriod $period The DatePeriod to wrap.
+     * @throws \InvalidArgumentException If the period has a zero interval which would cause an infinite loop.
      */
     public function __construct(DatePeriod $period)
     {
+        if (static::isZeroInterval($period->getDateInterval())) {
+            throw new InvalidArgumentException(
+                'Cannot create a period with a zero interval. This would cause an infinite loop when iterating.',
+            );
+        }
+
         /** @var \Iterator<int, \DateTimeInterface> $iterator */
         $iterator = $period->getIterator();
         $this->iterator = $iterator;
     }
 
+    /**
+     * Check if a DateInterval is effectively zero.
+     *
+     * @param \DateInterval $interval The interval to check.
+     * @return bool True if the interval is zero.
+     */
+    protected static function isZeroInterval(DateInterval $interval): bool
+    {
+        return $interval->y === 0
+            && $interval->m === 0
+            && $interval->d === 0
+            && $interval->h === 0
+            && $interval->i === 0
+            && $interval->s === 0
+            && (int)($interval->f * 1_000_000) === 0;
+    }
+
     /**
      * @return \Cake\Chronos\Chronos
      */

tests/TestCase/ChronosDatePeriodTest.php

@@ -19,6 +19,7 @@
 use DateInterval;
 use DatePeriod;
 use DateTime;
+use InvalidArgumentException;
 
 class ChronosDatePeriodTest extends TestCase
 {
@@ -30,11 +31,37 @@ public function testChronosPeriod(): void
             $output[$key] = $value;
         }
         $this->assertCount(4, $output);
-        $this->assertInstanceOf(ChronosDAte::class, $output[0]);
+        $this->assertInstanceOf(ChronosDate::class, $output[0]);
         $this->assertSame('2025-01-01 00:00:00', $output[0]->format('Y-m-d H:i:s'));
         $this->assertInstanceOf(ChronosDate::class, $output[1]);
         $this->assertSame('2025-01-02 00:00:00', $output[1]->format('Y-m-d H:i:s'));
         $this->assertInstanceOf(ChronosDate::class, $output[3]);
         $this->assertSame('2025-01-04 00:00:00', $output[3]->format('Y-m-d H:i:s'));
     }
+
+    public function testZeroIntervalThrowsException(): void
+    {
+        $this->expectException(InvalidArgumentException::class);
+        $this->expectExceptionMessage('Cannot create a period with a zero interval');
+
+        $period = new DatePeriod(
+            new DateTime('2025-01-01'),
+            new DateInterval('PT0S'),
+            new DateTime('2025-01-02'),
+        );
+        new ChronosDatePeriod($period);
+    }
+
+    public function testZeroIntervalAllZeroComponents(): void
+    {
+        $this->expectException(InvalidArgumentException::class);
+
+        $interval = new DateInterval('P0D');
+        $period = new DatePeriod(
+            new DateTime('2025-01-01'),
+            $interval,
+            new DateTime('2025-01-02'),
+        );
+        new ChronosDatePeriod($period);
+    }
 }

tests/TestCase/ChronosPeriodTest.php

@@ -19,6 +19,7 @@
 use DateInterval;
 use DatePeriod;
 use DateTime;
+use InvalidArgumentException;
 
 class ChronosPeriodTest extends TestCase
 {
@@ -35,4 +36,30 @@ public function testChronosPeriod(): void
         $this->assertInstanceOf(Chronos::class, $output[1]);
         $this->assertSame('2025-01-01 01:00:00', $output[1]->format('Y-m-d H:i:s'));
     }
+
+    public function testZeroIntervalThrowsException(): void
+    {
+        $this->expectException(InvalidArgumentException::class);
+        $this->expectExceptionMessage('Cannot create a period with a zero interval');
+
+        $period = new DatePeriod(
+            new DateTime('2025-01-01'),
+            new DateInterval('PT0S'),
+            new DateTime('2025-01-02'),
+        );
+        new ChronosPeriod($period);
+    }
+
+    public function testZeroIntervalAllZeroComponents(): void
+    {
+        $this->expectException(InvalidArgumentException::class);
+
+        $interval = new DateInterval('P0D');
+        $period = new DatePeriod(
+            new DateTime('2025-01-01'),
+            $interval,
+            new DateTime('2025-01-02'),
+        );
+        new ChronosPeriod($period);
+    }
 }