make assemblystream seekable

Signed-off-by: Robin Appelman <robin@icewind.nl>

apps/dav/lib/Upload/AssemblyStream.php

@@ -83,12 +83,47 @@ public function stream_open($path, $mode, $options, &$opened_path) {
 	}
 
 	/**
-	 * @param string $offset
+	 * @param int $offset
 	 * @param int $whence
 	 * @return bool
 	 */
 	public function stream_seek($offset, $whence = SEEK_SET) {
-		return false;
+		if ($whence === SEEK_CUR) {
+			$offset = $this->stream_tell() + $offset;
+		} else if ($whence === SEEK_END) {
+			$offset = $this->size + $offset;
+		}
+
+		if ($offset > $this->size) {
+			throw new \Exception('invalid offset');
+			return false;
+		}
+
+		$nodeIndex = 0;
+		$nodeStart = 0;
+		while (true) {
+			if (!isset($this->nodes[$nodeIndex + 1])) {
+				break;
+			}
+			$node = $this->nodes[$nodeIndex];
+			if ($nodeStart + $node->getSize() > $offset) {
+				break;
+			}
+			$nodeIndex++;
+			$nodeStart += $node->getSize();
+		}
+
+		$stream = $this->getStream($this->nodes[$nodeIndex]);
+		$nodeOffset = $offset - $nodeStart;
+		if(fseek($stream, $nodeOffset) === -1) {
+			return false;
+		}
+		$this->currentNode = $nodeIndex;
+		$this->currentNodeRead = $nodeOffset;
+		$this->currentStream = $stream;
+		$this->pos = $offset;
+
+		return true;
 	}
 
 	/**

apps/dav/tests/unit/Upload/AssemblyStreamTest.php

@@ -54,6 +54,21 @@ public function testGetContentsFread($expected, $nodes) {
 		$this->assertEquals($expected, $content);
 	}
 
+	/**
+	 * @dataProvider providesNodes()
+	 */
+	public function testSeek($expected, $nodes) {
+		$stream = \OCA\DAV\Upload\AssemblyStream::wrap($nodes);
+
+		$offset = floor(strlen($expected) * 0.6);
+		if(fseek($stream, $offset) === -1) {
+			$this->fail('fseek failed');
+		}
+
+		$content = stream_get_contents($stream);
+		$this->assertEquals(substr($expected, $offset), $content);
+	}
+
 	function providesNodes() {
 		$data8k = $this->makeData(8192);
 		$dataLess8k = $this->makeData(8191);