jkuchar/FileDownloader

<?php declare(strict_types=1);
/**
 * This file is part of FileDownloader.
 */

namespace BlockReader;

use FileDownloader\CannotSeekToPosition;

final class NativeBlockReader
{
    private $filePointer;
    private $fromByte;
    private $toByte;
    private $blockSize;

    /**
     * @param resource $filePointer
     * @param int $fromByte
     * @param int $toByte
     * @param int $blockSize
     */
    public function __construct($filePointer, $fromByte, $toByte, $blockSize)
    {
        $this->filePointer = $filePointer;
        $this->fromByte = $fromByte;
        $this->toByte = $toByte;
        $this->blockSize = $blockSize;
    }


    /**
     * @param callable $callback
     * @throws CannotSeekToPosition
     */
    public function start(callable $callback)
    {
        $fp = $this->filePointer;

        if(fseek($fp, $this->fromByte, SEEK_SET) === -1) { // Move file pointer to the start of the download
            // Can not move pointer to beginning of the filetransfer
            throw new CannotSeekToPosition();
        }

        // We are at the beginning
        $position = $this->fromByte;

        $bufferSize = $this->blockSize;
        while(!feof($fp) && $position <= $this->toByte) {
            if ($position + $bufferSize > $this->toByte) {
                // In case we're only outputtin a chunk, make sure we don't
                // read past the length
                $bufferSize = $this->toByte - $position + 1;
            }
            $data = fread($fp, $bufferSize);

            if($callback($data, $position) === FALSE) {
                return;
            }

            $position += strlen($data);
            unset($data);
        }
    }
}