title: Cannot get local candidate for WebRTC in iOS safari
body: <p>I only want to transfer data though WebRTC, so I didn't add <code>addStream</code> to <code>RTCPeerConnection</code>. What I need is <code>"sdpMid":"data"</code> local wlan candidates.</p>
  
  <p>When in local WIFI network, the <code>onicecandidate</code> event won't return a local candidate in iOS 11 Safari.</p>
  
  <p>When using a STUN server, it can return a remote candidate, but still no local candidate.</p>
  
  <p>How to fix this? </p>
  
  <p>--------------------------- UPDATE ----------------------------------------</p>
  
  <p>I have to use <code>navigator.mediaDevices.getUserMedia({audio: true})</code> to activate local candidate...
  Only with this command, then iOS Safari can get the local candidate and open channel in LAN environment.</p>
  
  <p>Don't know if it's an iOS bug.</p>