www/lib/aws_v3/Aws/S3/ApplyChecksumMiddleware.php
<?php
namespace Aws\S3;

use Aws\CommandInterface;
use GuzzleHttp\Psr7;
use Psr\Http\Message\RequestInterface;

/**
 * Apply required or optional MD5s to requests before sending.
 *
 * IMPORTANT: This middleware must be added after the "build" step.
 *
 * @internal
 */
class ApplyChecksumMiddleware
{
    private static $md5 = [
        'DeleteObjects',
        'PutBucketCors',
        'PutBucketLifecycle',
        'PutBucketLifecycleConfiguration',
        'PutBucketPolicy',
        'PutBucketTagging',
        'PutBucketReplication',
    ];

    private static $sha256 = [
        'PutObject',
        'UploadPart',
    ];

    private $nextHandler;

    /**
     * Create a middleware wrapper function.
     *
     * @return callable
     */
    public static function wrap()
    {
        return function (callable $handler) {
            return new self($handler);
        };
    }

    public function __construct(callable $nextHandler)
    {
        $this->nextHandler = $nextHandler;
    }

    public function __invoke(
        CommandInterface $command,
        RequestInterface $request
    ) {
        $next = $this->nextHandler;
        $name = $command->getName();
        $body = $request->getBody();

        if (in_array($name, self::$md5) && !$request->hasHeader('Content-MD5')) {
            // Set the content MD5 header for operations that require it.
            $request = $request->withHeader(
                'Content-MD5',
                base64_encode(Psr7\hash($body, 'md5', true))
            );
        } elseif (in_array($name, self::$sha256) && $command['ContentSHA256']) {
            // Set the content hash header if provided in the parameters.
            $request = $request->withHeader(
                'X-Amz-Content-Sha256',
                $command['ContentSHA256']
            );
        }

        return $next($command, $request);
    }
}
