--- /dev/null
+<?php
+/**
+ * Zend Framework (http://framework.zend.com/)
+ *
+ * @see http://github.com/zendframework/zend-diactoros for the canonical source repository
+ * @copyright Copyright (c) 2015-2016 Zend Technologies USA Inc. (http://www.zend.com)
+ * @license https://github.com/zendframework/zend-diactoros/blob/master/LICENSE.md New BSD License
+ */
+
+namespace Zend\Diactoros;
+
+use Psr\Http\Message\StreamInterface;
+use RuntimeException;
+
+/**
+ * Class RelativeStream
+ *
+ * Wrapper for default Stream class, representing subpart (starting from given offset) of initial stream.
+ * It can be used to avoid copying full stream, conserving memory.
+ * @example see Zend\Diactoros\AbstractSerializer::splitStream()
+ */
+final class RelativeStream implements StreamInterface
+{
+ /**
+ * @var StreamInterface
+ */
+ private $decoratedStream;
+
+ /**
+ * @var int
+ */
+ private $offset;
+
+ /**
+ * Class constructor
+ *
+ * @param StreamInterface $decoratedStream
+ * @param int $offset
+ */
+ public function __construct(StreamInterface $decoratedStream, $offset)
+ {
+ $this->decoratedStream = $decoratedStream;
+ $this->offset = (int)$offset;
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function __toString()
+ {
+ $this->seek(0);
+ return $this->getContents();
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function close()
+ {
+ $this->decoratedStream->close();
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function detach()
+ {
+ return $this->decoratedStream->detach();
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function getSize()
+ {
+ return $this->decoratedStream->getSize() - $this->offset;
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function tell()
+ {
+ return $this->decoratedStream->tell() - $this->offset;
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function eof()
+ {
+ return $this->decoratedStream->eof();
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function isSeekable()
+ {
+ return $this->decoratedStream->isSeekable();
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function seek($offset, $whence = SEEK_SET)
+ {
+ if ($whence == SEEK_SET) {
+ return $this->decoratedStream->seek($offset + $this->offset, $whence);
+ }
+ return $this->decoratedStream->seek($offset, $whence);
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function rewind()
+ {
+ return $this->seek(0);
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function isWritable()
+ {
+ return $this->decoratedStream->isWritable();
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function write($string)
+ {
+ if ($this->tell() < 0) {
+ throw new RuntimeException('Invalid pointer position');
+ }
+ return $this->decoratedStream->write($string);
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function isReadable()
+ {
+ return $this->decoratedStream->isReadable();
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function read($length)
+ {
+ if ($this->tell() < 0) {
+ throw new RuntimeException('Invalid pointer position');
+ }
+ return $this->decoratedStream->read($length);
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function getContents()
+ {
+ if ($this->tell() < 0) {
+ throw new RuntimeException('Invalid pointer position');
+ }
+ return $this->decoratedStream->getContents();
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function getMetadata($key = null)
+ {
+ return $this->decoratedStream->getMetadata($key);
+ }
+}