Draft: [Feature] Add mDNS Discovery

Advertise IP address through mDNS (Bonjour) so LanLinkProvider can send UDP packets to those addresses directly.

Counterparts

• Android: kdeconnect-android!91 (closed)
• Desktop: kdeconnect-kde!147 (closed)

Protocol

Requires an additional IP address field ("ip") in TXT Record because even Apple sample code can't connect to each other here at UW 😞

service type: "_kdeconnect._tcp"
service name: "KDE Connect on " + deviceName
service port: TCP port
service addr: TCP addr
TXT record:
  name: deviceName, String
  id: deviceId, String
  type: deviceType, not localized, String
  version: protocolVersion, String
+ ip: service addr (e.g. "1.1.1.1"), String (NEW), REQUIRED

References

• Apple sample code: Building a Custom Peer-to-Peer Protocol
  • NWBrowser can't get IP and port, require NWConnection or NetService (deprecated)
  • NWListener cannot set port to be the same as the TCP port on real device
    • https://developer.apple.com/forums/thread/129452
    • https://openradar.appspot.com/FB8658821 (reported Sep 2020)

Additional Notes

• On University of Washington's restricted network, sometimes even AirDrop can't discover other devices.
• We might be able to use this to tell if we have Local Network permission (which is essential for this app to work)