PHPLIB-213: Support seeking and partial file retrieval for GridFS streams

src/GridFS/ReadableStream.php

@@ -166,6 +166,44 @@ class ReadableStream
         return $data;
     }
 
+    /**
+     * Seeks the chunk and buffer offsets for the next read operation.
+     *
+     * @param integer $offset
+     * @throws InvalidArgumentException if $offset is out of range
+     */
+    public function seek($offset)
+    {
+        if ($offset < 0 || $offset > $this->file->length) {
+            throw new InvalidArgumentException(sprintf('$offset must be >= 0 and <= %d; given: %d', $length, $offset));
+        }
+
+        /* Compute the offsets for the chunk and buffer (i.e. chunk data) from
+         * which we will expect to read after seeking. If the chunk offset
+         * changed, we'll also need to reset the buffer.
+         */
+        $lastChunkOffset = $this->chunkOffset;
+        $this->chunkOffset = (integer) floor($offset / $this->chunkSize);
+        $this->bufferOffset = $offset % $this->chunkSize;
+
+        if ($lastChunkOffset !== $this->chunkOffset) {
+            $this->buffer = null;
+            $this->chunksIterator = null;
+        }
+    }
+
+    /**
+     * Return the current position of the stream.
+     *
+     * This is the offset within the stream where the next byte would be read.
+     *
+     * @return integer
+     */
+    public function tell()
+    {
+        return ($this->chunkOffset * $this->chunkSize) + $this->bufferOffset;
+    }
+
     /**
      * Initialize the buffer to the current chunk's data.
      *

src/GridFS/StreamWrapper.php

@@ -136,6 +136,40 @@ class StreamWrapper
         }
     }
 
+    /**
+     * Return the current position of the stream.
+     *
+     * @see http://php.net/manual/en/streamwrapper.stream-seek.php
+     * @param integer $offset Stream offset to seek to
+     * @param integer $whence One of SEEK_SET, SEEK_CUR, or SEEK_END
+     * @return boolean True if the position was updated and false otherwise
+     */
+    public function stream_seek($offset, $whence = \SEEK_SET)
+    {
+        $size = $this->stream->getSize();
+
+        if ($whence === \SEEK_CUR) {
+            $offset += $this->stream->tell();
+        }
+
+        if ($whence === \SEEK_END) {
+            $offset += $size;
+        }
+
+        // WritableStreams are always positioned at the end of the stream
+        if ($this->stream instanceof WritableStream) {
+            return $offset === $size;
+        }
+
+        if ($offset < 0 || $offset > $size) {
+            return false;
+        }
+
+        $this->stream->seek($offset);
+
+        return true;
+    }
+
     /**
      * Return information about the stream.
      *
@@ -166,6 +200,17 @@ class StreamWrapper
         return $stat;
     }
 
+    /**
+     * Return the current position of the stream.
+     *
+     * @see http://php.net/manual/en/streamwrapper.stream-tell.php
+     * @return integer The current position of the stream
+     */
+    public function stream_tell()
+    {
+        return $this->stream->tell();
+    }
+
     /**
      * Write bytes to the stream.
      *

src/GridFS/WritableStream.php

@@ -161,6 +161,21 @@ class WritableStream
         return $this->length + strlen($this->buffer);
     }
 
+    /**
+     * Return the current position of the stream.
+     *
+     * This is the offset within the stream where the next byte would be
+     * written. Since seeking is not supported and writes are appended, this is
+     * always the end of the stream.
+     *
+     * @see WriteableStream::getSize()
+     * @return integer
+     */
+    public function tell()
+    {
+        return $this->getSize();
+    }
+
     /**
      * Inserts binary data into GridFS via chunks.
      *

tests/GridFS/StreamWrapperFunctionalTest.php

@@ -50,6 +50,32 @@ class StreamWrapperFunctionalTest extends FunctionalTestCase
         $this->assertSame('', fread($stream, 3));
     }
 
+    public function testReadableStreamSeek()
+    {
+        $stream = $this->bucket->openDownloadStream('length-10');
+
+        $this->assertSame(0, fseek($stream, 2, \SEEK_SET));
+        $this->assertSame('cde', fread($stream, 3));
+        $this->assertSame(0, fseek($stream, 10, \SEEK_SET));
+        $this->assertSame('', fread($stream, 3));
+        $this->assertSame(-1, fseek($stream, -1, \SEEK_SET));
+        $this->assertSame(-1, fseek($stream, 11, \SEEK_SET));
+
+        $this->assertSame(0, fseek($stream, -5, \SEEK_CUR));
+        $this->assertSame('fgh', fread($stream, 3));
+        $this->assertSame(0, fseek($stream, 1, \SEEK_CUR));
+        $this->assertSame('j', fread($stream, 3));
+        $this->assertSame(-1, fseek($stream, 1, \SEEK_CUR));
+        $this->assertSame(-1, fseek($stream, -11, \SEEK_CUR));
+
+        $this->assertSame(0, fseek($stream, 0, \SEEK_END));
+        $this->assertSame('', fread($stream, 3));
+        $this->assertSame(0, fseek($stream, -8, \SEEK_END));
+        $this->assertSame('cde', fread($stream, 3));
+        $this->assertSame(-1, fseek($stream, -11, \SEEK_END));
+        $this->assertSame(-1, fseek($stream, 1, \SEEK_END));
+    }
+
     public function testReadableStreamStat()
     {
         $stream = $this->bucket->openDownloadStream('length-10');
@@ -102,6 +128,25 @@ class StreamWrapperFunctionalTest extends FunctionalTestCase
         $this->assertSame('', fread($stream, 8192));
     }
 
+    public function testWritableStreamSeek()
+    {
+        $stream = $this->bucket->openUploadStream('filename');
+
+        $this->assertSame(6, fwrite($stream, 'foobar'));
+
+        $this->assertSame(-1, fseek($stream, 0, \SEEK_SET));
+        $this->assertSame(-1, fseek($stream, 7, \SEEK_SET));
+        $this->assertSame(0, fseek($stream, 6, \SEEK_SET));
+
+        $this->assertSame(0, fseek($stream, 0, \SEEK_CUR));
+        $this->assertSame(-1, fseek($stream, -1, \SEEK_CUR));
+        $this->assertSame(-1, fseek($stream, 1, \SEEK_CUR));
+
+        $this->assertSame(0, fseek($stream, 0, \SEEK_END));
+        $this->assertSame(-1, fseek($stream, -1, \SEEK_END));
+        $this->assertSame(-1, fseek($stream, 1, \SEEK_END));
+    }
+
     public function testWritableStreamStat()
     {
         $currentTimestamp = time();