title: What are the consequences of not including a content-length header in a server response?
body: <p>The <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.13" rel="noreferrer">RFC</a> says the <code>content-length</code> header is optional ("..Applications SHOULD use this field...").  </p>
  
  <p>From what I can gather if its not included then the client will not know how much data to expect, therefore will not be able to show a determinate progress bar when downloading the body (i.e. the top bar instead of the bottom).</p>
  
  <p><img src="https://i.stack.imgur.com/xA6K5.png" alt="progress"></p>
  
  <p>Are there any other side effects or bugs that arise from omitting this header?</p>