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<?phpnamespace Aws\Signature;
 
 use Aws\Credentials\CredentialsInterface;
 use Psr\Http\Message\RequestInterface;
 
 /**
 * Amazon S3 signature version 4 support.
 */
 class S3SignatureV4 extends SignatureV4
 {
 /**
 * Always add a x-amz-content-sha-256 for data integrity.
 */
 public function signRequest(
 RequestInterface $request,
 CredentialsInterface $credentials
 ) {
 if (!$request->hasHeader('x-amz-content-sha256')) {
 $request = $request->withHeader(
 'X-Amz-Content-Sha256',
 $this->getPayload($request)
 );
 }
 
 return parent::signRequest($request, $credentials);
 }
 
 /**
 * Override used to allow pre-signed URLs to be created for an
 * in-determinate request payload.
 */
 protected function getPresignedPayload(RequestInterface $request)
 {
 return 'UNSIGNED-PAYLOAD';
 }
 
 /**
 * Amazon S3 does not double-encode the path component in the canonical request
 */
 protected function createCanonicalizedPath($path)
 {
 return '/' . ltrim($path, '/');
 }
 }
 
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