src/Google/Http/MediaFileUpload.php
public function nextChunk($chunk = false)
  {
    $resumeUri = $this->getResumeUri();

    if (false == $chunk) {
      $chunk = substr($this->data, $this->progress, $this->chunkSize);
    }

    $lastBytePos = $this->progress + strlen($chunk) - 1;
    $headers = array(
      'content-range' => "bytes $this->progress-$lastBytePos/$this->size",
      'content-length' => strlen($chunk),
      'expect' => '',
    );

    $request = new Request(
        'PUT',
        $resumeUri,
        $headers,
        Psr7\stream_for($chunk)
    );

    return $this->makePutRequest($request);
  }
public function nextChunk($chunk = false)
  {
    $resumeUri = $this->getResumeUri();

    if (false == $chunk) {
      $chunk = substr($this->data, $this->progress, $this->chunkSize);
    }

    $lastBytePos = $this->progress + strlen($chunk) - 1;
    $headers = array(
      'content-range' => "bytes $this->progress-$lastBytePos/$this->size",
      'content-length' => strlen($chunk),
      'expect' => '',
    );

    $request = new Request(
        'PUT',
        $resumeUri,
        $headers,
        Psr7\stream_for($chunk)
    );

    return $this->makePutRequest($request);
  }
Send the next part of the file to upload.
@param [$chunk] the next set of bytes to send. If false will used $data passed
at construct time.