title: How to know Content-length
body: <p>I want to be able to know the size of a remote file without downloading it. I know there are some solutions using the "Content-length" header value, but for some links this header is missing. In that case, a solution would be to download the whole file, but what happens if the file is bigger than 1Gb for example.</p>
  
  <p>What is the way download managers use to find out the size of a remote file?</p>
  
  <p>If you have any solution in any languages, I will take it. Thank you.</p>