title: How to check an AWS S3 key for existence with the AWS CPP SDK?
body: <p>I use the <strong>S3 SDK CPP</strong> and have the following cenario:</p>
  
  <ol>
  <li>I get some information sent from a client to my server (client wants to download from <em>S3</em>)</li>
  <li>With the information sent I create a <em>S3</em> key</li>
  <li>I want to check if the key exists (has a file) on the <em>S3</em></li>
  <li>I create a presigned URL that allows the client to download a file from <em>S3</em></li>
  <li>Send URL to client</li>
  <li>Client downloads the file</li>
  </ol>
  
  <p>Before I execute step 4 I want to check if the key really exists on the S3. The client can't download a file that does not exist anyway.</p>
  
  <p>I have an <code>AWS::S3Client</code> object. Do I really need to create a <em>TransferManager</em> for this or is there a simple way to handle this with the client object?</p>
  
  <p>The client itself does not have a relation to <em>S3</em> so I can't check it there. The server has to do all the work.</p>