Disallow cloning Stream objects

Streams hold a reference to the stateful resource handle for their actual
contents. Cloning a Stream will not actually clone the underlying resource,
thus both streams would still refer to the same resource after cloning and any
changes in one stream object would be reflected in the other object. This
violates user expectations after a cloning operation.

Disallow cloning entirely as the safe default choice. Alternatively a new
stream could be created and attached and the contents could be copied over.
This can get expensive with larger or infinite streams, though.

Signed-off-by: Tim Düsterhus <duesterhus@woltlab.com>

src/Stream.php

@@ -364,4 +364,11 @@ private function isValidStreamResourceType(mixed $resource): bool
 
         return false;
     }
+
+    /**
+     * Disallow stream cloning.
+     */
+    private function __clone()
+    {
+    }
 }

test/StreamTest.php

@@ -5,6 +5,7 @@
 namespace LaminasTest\Diactoros;
 
 use CurlHandle;
+use Error;
 use GdImage;
 use InvalidArgumentException;
 use Laminas\Diactoros\Stream;
@@ -679,4 +680,18 @@ public function testSizeReportsNullForPhpInputStreams(): void
         $stream   = new Stream($resource);
         $this->assertNull($stream->getSize());
     }
+
+    public function testStreamsAreUnclonable(): void
+    {
+        $stream = new Stream(fopen('php://temp', 'r+'));
+        $stream->write('foo');
+
+        $this->assertSame('foo', $stream->__toString());
+
+        $this->expectException(Error::class);
+        $this->expectExceptionMessage('private Laminas\Diactoros\Stream::__clone()');
+
+        /** @psalm-suppress InvalidClone */
+        clone $stream;
+    }
 }