Correct stream caching, write permissions, and position tracking

packages/stream/src/DecoratorStream.php

@@ -15,9 +15,7 @@ class DecoratorStream implements StreamInterface
 
     public function __construct(?StreamInterface $target = null)
     {
-        if ($target) {
-            $this->stream = $target;
-        }
+        $this->stream = $target ?? new Stream();
     }
 
     public function __toString(): string

packages/stream/src/PhpInputStream.php

@@ -29,7 +29,7 @@ protected function __construct(?StreamInterface $cache = null)
 
     public static function getInstance(?StreamInterface $cache = null): self
     {
-        return self::$instance ?? new PhpInputStream($cache);
+        return self::$instance ??= new self($cache);
     }
 
     public static function getInstanceAndCached(?StreamInterface $cache = null): self

packages/stream/src/StringStream.php

@@ -262,6 +262,10 @@ public function isWritable(): bool
      */
     public function write($string): int
     {
+        if (!$this->isWritable()) {
+            throw new RuntimeException('Stream is not writable');
+        }
+
         $length = strlen($string);
 
         $start = substr($this->resource, 0, $this->pointer);
@@ -326,6 +330,9 @@ public function getContents(): string
             return '';
         }
 
+        $this->pointer += strlen($result);
+        $this->readPosition = $this->pointer;
+
         return $result;
     }
 

packages/stream/test/DecoratorStreamTest.php

@@ -19,6 +19,14 @@ public function constructAcceptsInnerStream(): void
         $this->assertSame($inner, new DecoratorStream($inner)->getInnerStream());
     }
 
+    #[Test]
+    public function constructWithoutTargetCreatesEmptyStream(): void
+    {
+        $decorator = new DecoratorStream();
+
+        $this->assertSame('', $decorator->getContents());
+    }
+
     #[Test]
     public function setInnerStreamReplacesTarget(): void
     {

packages/stream/test/PhpInputStreamTest.php

@@ -23,6 +23,9 @@ public function getInstanceAndCachedReturnsRewoundStreamWithInputContents(): voi
     #[Test]
     public function getInstanceCreatesStreamWithGivenCache(): void
     {
-        $this->assertInstanceOf(PhpInputStream::class, PhpInputStream::getInstance());
+        $stream = PhpInputStream::getInstance();
+
+        $this->assertInstanceOf(PhpInputStream::class, $stream);
+        $this->assertSame($stream, PhpInputStream::getInstance());
     }
 }

packages/stream/test/StringStreamTest.php

@@ -284,6 +284,8 @@ public function getContentsReturnsRemainingStringFromPosition(): void
         $stream->seek(2);
 
         $this->assertEquals('O BAR', $stream->getContents());
+        $this->assertSame(7, $stream->tell());
+        $this->assertSame('', $stream->getContents());
     }
 
     #[Test]
@@ -384,4 +386,16 @@ public function writableControlsIsWritable(): void
 
         $this->assertTrue($stream->isWritable());
     }
+
+    #[Test]
+    public function writableFalseBlocksWrite(): void
+    {
+        $stream = new StringStream('FOO', READ_WRITE_FROM_BEGIN);
+        $stream->writable(false);
+
+        $this->expectException(RuntimeException::class);
+        $this->expectExceptionMessageIs('Stream is not writable');
+
+        $stream->write('BAR');
+    }
 }