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Editing: ValidateResponseChecksumParser.php

<?php
namespace Aws\S3;

use Aws\Api\Parser\AbstractParser;
use Aws\Api\Service;
use Aws\Api\StructureShape;
use Aws\CommandInterface;
use Aws\S3\Exception\S3Exception;
use Psr\Http\Message\ResponseInterface;
use Psr\Http\Message\StreamInterface;

/**
 * @internal Decorates a parser for the S3 service to validate the response checksum.
 */
class ValidateResponseChecksumParser extends AbstractParser
{
    use CalculatesChecksumTrait;
    /**
     * @param callable $parser Parser to wrap.
     */
    public function __construct(callable $parser, Service $api)
    {
        $this->api = $api;
        $this->parser = $parser;
    }

public function __invoke(
        CommandInterface $command,
        ResponseInterface $response
    ) {
        $fn = $this->parser;
        $result = $fn($command, $response);

//Skip this middleware if the operation doesn't have an httpChecksum
        $op = $this->api->getOperation($command->getName());
        $checksumInfo = isset($op['httpChecksum'])
            ? $op['httpChecksum']
            : [];
        if (empty($checksumInfo)) {
            return $result;
        }

//Skip this middleware if the operation doesn't send back a checksum, or the user doesn't opt in
        $checksumModeEnabledMember = isset($checksumInfo['requestValidationModeMember'])
            ? $checksumInfo['requestValidationModeMember']
            : "";
        $checksumModeEnabled = isset($command[$checksumModeEnabledMember])
            ? $command[$checksumModeEnabledMember]
            : "";
        $responseAlgorithms = isset($checksumInfo['responseAlgorithms'])
            ? $checksumInfo['responseAlgorithms']
            : [];
        if (empty($responseAlgorithms)
            || strtolower($checksumModeEnabled) !== "enabled"
        ) {
            return $result;
        }

if (extension_loaded('awscrt')) {
            $checksumPriority = ['CRC32C', 'CRC32', 'SHA1', 'SHA256'];
        } else {
            $checksumPriority = ['CRC32', 'SHA1', 'SHA256'];
        }
        $checksumsToCheck = array_intersect($responseAlgorithms, $checksumPriority);
        $checksumValidationInfo = $this->validateChecksum($checksumsToCheck, $response);

if ($checksumValidationInfo['status'] == "SUCCEEDED") {
            $result['ChecksumValidated'] = $checksumValidationInfo['checksum'];
        } else if ($checksumValidationInfo['status'] == "FAILED"){
            //Ignore failed validations on GetObject if it's a multipart get which returned a full multipart object
            if ($command->getName() == "GetObject"
                && !empty($checksumValidationInfo['checksumHeaderValue'])
            ) {
                $headerValue = $checksumValidationInfo['checksumHeaderValue'];
                $lastDashPos = strrpos($headerValue, '-');
                $endOfChecksum = substr($headerValue, $lastDashPos + 1);
                if (is_numeric($endOfChecksum)
                    && intval($endOfChecksum) > 1
                    && intval($endOfChecksum) < 10000) {
                    return $result;
                }
            }
            throw new S3Exception(
                "Calculated response checksum did not match the expected value",
                $command
            );
        }
        return $result;
    }

public function parseMemberFromStream(
        StreamInterface $stream,
        StructureShape $member,
        $response
    ) {
        return $this->parser->parseMemberFromStream($stream, $member, $response);
    }

/**
     * @param $checksumPriority
     * @param ResponseInterface $response
     */
    public function validateChecksum($checksumPriority, ResponseInterface $response)
    {
        $checksumToValidate = $this->chooseChecksumHeaderToValidate(
            $checksumPriority,
            $response
        );
        $validationStatus = "SKIPPED";
        $checksumHeaderValue = null;
        if (!empty($checksumToValidate)) {
            $checksumHeaderValue = $response->getHeader(
                'x-amz-checksum-' . $checksumToValidate
            );
            if (isset($checksumHeaderValue)) {
                $checksumHeaderValue = $checksumHeaderValue[0];
                $calculatedChecksumValue = $this->getEncodedValue(
                    $checksumToValidate,
                    $response->getBody()
                );
                $validationStatus = $checksumHeaderValue == $calculatedChecksumValue
                    ? "SUCCEEDED"
                    : "FAILED";
            }
        }
        return [
            "status" => $validationStatus,
            "checksum" => $checksumToValidate,
            "checksumHeaderValue" => $checksumHeaderValue,
        ];
    }

/**
     * @param $checksumPriority
     * @param ResponseInterface $response
     */
    public function chooseChecksumHeaderToValidate(
        $checksumPriority,
        ResponseInterface $response
    ) {
        foreach ($checksumPriority as $checksum) {
            $checksumHeader = 'x-amz-checksum-' . $checksum;
            if ($response->hasHeader($checksumHeader)) {
                return $checksum;
            }
        }
        return null;
    }
}

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