ZipStream.php

<?php
namespace App\Services;

use App\Models\ZipFile;
use Illuminate\Support\Collection;
use ZipStream\Exception\FileNotFoundException;
use ZipStream\ZipStream as ZipStreamBase;

class ZipStream extends ZipStreamBase
{
    /**
     * @var array
     */
    protected $fileList = [];

    /**
     * @var int
     */
    protected $fileSizes = 0;

    /**
     * @var int
     */
    protected $filepathLengths = 0;

    /**
     * @var int
     */
    protected $bytesSent = 0;

    /**
     * @var
     */
    protected $cacheStream;

    /**
     * @param null  $name
     * @param array $opt
     */
    public function __construct($name = null, $opt = [])
    {
        // We want all files treated like large files, which uses 'store' and no compression
        $opt['large_file_size'] = 1;

        parent::__construct($name, $opt);
    }

    /**
     * @param $name
     *
     * @return $this
     */
    public function setName($name)
    {
        $this->output_name  = $name;
        $this->need_headers = $name || $this->opt[self::OPTION_SEND_HTTP_HEADERS];

        return $this;
    }

    /**
     * Hand me a writable output stream to this method, and we'll save the zip data as we stream it out.
     *
     * @param $stream
     */
    public function cacheZip($stream)
    {
        $this->cacheStream = $stream;
    }

    /**
     * @param String $str
     */
    protected function send($str) {
        $this->bytesSent += strlen($str);

        if(is_resource($this->cacheStream)) {
            fwrite($this->cacheStream, $str);
        }

        parent::send($str);
    }

    /**
     * @param Collection $fileList
     *
     * @return $this
     */
    public function queue(Collection $fileList)
    {
        $fileList->each(function ($file) {
            $this->queueFile($file);
        });

        return $this;
    }

    /**
     * @param ZipFile $file
     */
    public function queueFile(ZipFile $file)
    {
        if(array_key_exists($file->getAbsolutePath(), $this->fileList)) {
            return;
        }

        $this->fileList[$file->getAbsolutePath()] = $file;
        $this->fileSizes += max(2, $file->getFilesize());
        $this->filepathLengths += strlen($file->getZipPath());
    }

    /**
     * @param string $cachePath
     *
     * @return $this
     */
    public function process($cachePath = null)
    {
        if(is_null($cachePath) || !is_writable(dirname($cachePath))) {
            $this->buildAndSend();
            return $this;
        }

        $this->cacheStream = fopen($cachePath, 'w');
        $this->buildAndSend();
        fclose($this->cacheStream);

        return $this;
    }

    /**
     *
     */
    protected function buildAndSend()
    {
        $this->sendContentLengthHeader();

        foreach($this->fileList AS $file) {
            $this->processFile($file);
        }

        $this->finish();
    }

    /**
     * @param $file
     *
     * @throws FileNotFoundException
     * @throws \ZipStream\Exception\FileNotReadableException
     */
    protected function processFile(ZipFile $file)
    {
        if(starts_with($file->getAbsolutePath(), "s3://")) {
            $this->addFileFromStream($file->getZipPath(), $file->getHandle());
            fclose($file->getHandle());
        } else {
            $this->addFileFromPath($file->getZipPath(), $file->getAbsolutePath());
        }
    }

    /**
     * @return int
     */
    public function getBytesSent()
    {
        return $this->bytesSent;
    }

    /**
     * We can do this!
     */
    protected function sendContentLengthHeader()
    {
        header("Content-Length: " . $this->calculateZipSize());
    }

    /**
     * See http://stackoverflow.com/a/19380600/660694
     *
     * @return int
     */
    public function calculateZipSize()
    {
        return count($this->fileList) * (30 + 46) + (2 * $this->filepathLengths) + $this->fileSizes + 22;
    }

    /**
     * @param callable $errorCallback
     *
     * @return $this
     */
    public function sanityCheckFileSize(callable $errorCallback)
    {
        if($this->calculateZipSize() != $this->getBytesSent()) {
            $errorCallback($this->calculateZipSize(), $this->getBytesSent());
        }

        return $this;
    }
}

Very insightful! Thank you very much!